MCIPs have been shown to inhibit calcineurin activity by binding directly to the CnA subunit (Fuentes, 2000). Whether Sra interacts with Drosophila calcineurin subunits, which were expressed in the female germline, was examined. In this experiment, Drosophila S2 cultured cells were first transfected with sra and Pp2B-14D-myc expression constructs and then immunoprecipitated them with Sra antibody. Immunoblotting with Myc antibody revealed that Sra indeed binds to Pp2B-14D. Thus, it is clear that Sra is capable of forming a complex with Pp2B-14D when coexpressed in S2 cells. It has been shown that calcineurin subunits are more stable when they form a complex. When CanB2 plasmid was cotransfected, an increased (2.7 times) amount of Pp2B-14D protein was coimmunoprecipitated together with CanB2. Western analysis of cell lysates suggested that Pp2B-14D, CanB2, and Sra are more stable when they were coexpressed. In addition to Pp2B-14D, it was also found that CanA-14F, another CnA subunit expressed in the germline, could bind to Sra, implying at least that it can form a complex with Pp2B-14D and CanB2 or CanA-14F and CanB2 (Takeo, 2006).
RNA in situ hybridization showed that sra mRNA is present in the central nervous system of the third instar larvae, with a relatively intense signal in the brain and weak signals in the ventral ganglion. A relatively low, but ubiquitous expression level was observed in leg and wing imaginal discs, and no signal was detected in the eye-antennal discs. A strong signal was detected in all neurons of the adult brain. There is no specific localization of mRNA within the brain. The gene was also expressed at high levels in the nurse cells and oocytes. These results support the idea that sra functions in neurons during oogenesis (Ejima, 2004).
Independent sarah (sra) alleles were found in genetic screens for sterile Drosophila females whose embryos arrest development very soon after fertilization. sarah corresponds to CG6072, which encodes calcipressin, a highly conserved inhibitor of the calcium- and calmodulin-dependent phosphatase, calcineurin (Ejima, 2004; Kingsbury, 2000). These sra mutations are at a minimum strong hypomorphs; the accompanying article by Takeo (2006) describes an authentic sra null allele whose phenotypic effects are very similar to those described in this study (Horner, 2006).
Mutations of sarah affect neither the fertility of males nor the viability of adults of either sex. However, sarah mutations have previously been shown to influence learning and memory (Chang, 2003), as well as ovulation and courtship behaviors (Ejima, 2004). Although sarah mutant females lay eggs, no embryos hatch (Ejima, 2004). To determine the underlying defect, these eggs and their precursors were examined in more detail. Oocytes within the ovaries of sra mutant females appear normal, as determined by staining for DNA and tubulin. In the wild-type, mature oocytes are arrested in metaphase I because the meiotic spindle pulls homologous chromosomes to opposite spindle poles while the homologs are held together by chiasmata, generating tension. This metaphase I arrest also occurred in all observed sra oocytes, as established by a single mass of chromatin at the midpoint of a single spindle. Thus, sra mutations do not affect bivalent formation or metaphase arrest prior to ovulation (Horner, 2006).
To characterize the developmental defect, heteroallelic sarah females and heterozygous control females were mated to wild-type males and allowed to lay eggs for 2 hr. Laid eggs were fixed and stained with propidium iodide to visualize the chromosomes and with α-tubulin antibodies to reveal the spindles. Eggs laid by control females developed as expected for 0–2 hr embryos; most had completed meiosis and were undergoing cleavage divisions and gastrulation (Horner, 2006).
In contrast, none of the eggs laid by sarah heteroallelic females progressed beyond meiosis, even though these females mated avidly with males and produced fertilized eggs. The characteristic phenotype was arrest during anaphase of the first meiotic division. A few eggs from mothers of certain presumably weaker genotypes showed other meiotic aberrations, probably due to low residual sra activity. Some anaphase I figures were abnormal, with chromosomes scattered throughout the spindle. A few eggs appeared to be in meiosis II because two spindles were observed. However, these two spindles were generally parallel to one another instead of end to end as in wild-type meiosis II, and the two spindles were usually asynchronous, with one in metaphase and the other in anaphase. In a few eggs, some pycnotic chromosomes appeared to have separated from the main spindle and nucleated secondary spindles. Apparently normal polar bodies formed in a single egg, so meiosis may rarely complete in eggs from mothers with the weakest sra alleles (Horner, 2006).
To verify that sra eggs usually arrest in anaphase I, they were examined by high-resolution Feulgen and Giemsa staining. In every arrested anaphase, three large chromosomes are directed toward the two poles of the spindle; occasionally, the tiny fourth chromosome is seen to lead each of the two groups of chromosomes. Sister chromatids must therefore remain attached (at least at their centromeres) during the anaphase movements. The accumulation of “middle pole” material that ordinarily forms late in anaphase I and eventually demarcates the boundary between the two metaphase II spindles was never seen, indicating that the arrest occurs early in anaphase I. Consistent with the fact that egg activation in Drosophila is independent of fertilization, the eggs laid by virgin sra mutant females also arrest at anaphase I (Horner, 2006).
Mutant germline clones were created via the FLP-dominant female sterile technique. The eggs produced by mutant germlines were double stained with Feulgen and Giemsa for high-resolution cytometry of meiotic figures. Anaphase I arrest was observed in all cases. The genotype of the germline therefore determines the sra mutant phenotype in eggs. Transcripts of sra accumulate to high levels in germline nurse cells and oocytes during oogenesis (Ejima, 2004).
The translation of Bicoid (Bcd) upon activation organizes anterior development in embryos. During oogenesis, bcd mRNA is synthesized in nurse cells and transported to oocytes, where it remains untranslated. Upon activation, bcd mRNA is rapidly polyadenylated and translated. To test for effects of sarah on bcd mRNA polyadenylation, the length of the poly(A) tails on bcd mRNAs was measured by using the PCR poly(A) test (PAT). In the wild-type, more than 120 A's are added to these RNAs within 1 hr of egg laying and activation. In contrast, eggs laid by sra mutant females add only about 64 nucleotides of poly(A) to bcd mRNA upon egg laying, similar to the 80 base extension that occurs in cortex mutants (Horner, 2006).
The failure of sra mutant eggs to fully polyadenylate bcd transcripts predicts these eggs will be compromised in their ability to translate Bcd protein. To test this assumption, lysates from fertilized, laid eggs of sra mutant females were probed for Bcd on Western blots. As controls, ovaries from wild-type females as well as fertilized and unfertilized laid eggs from wild-type and siblings heterozygous for the same sra alleles were also examined. In wild-type and heterozygous controls, Bcd is not observed in mature, unactivated oocytes but accumulates to high levels upon activation, as expected. However, no Bcd translation was observed in eggs laid by any sra mutants (Horner, 2006).
To ascertain whether VM (vitelline membrane) cross-linking occurs in sra eggs, mated females were allowed to lay eggs for 2 hr timed intervals, and these in vivo activated eggs were treated with 50% bleach for two minutes. Non-cross-linked eggs lysed within the 2 min incubation, but if VM cross-linking and subsequent eggshell hardening occurred, eggs became resistant to 50% bleach. Eggs laid by sra females undergo VM cross-linking to the same extent as those from heterozygous controls. In contrast, all mature stage-14 ovarian oocytes of all genotypes are lysed by bleach. Although VM cross-linking occurs in sra eggs activated in vivo by egg laying, results from in vitro activation suggest that the cross-linking may be slower or less efficient than in wild-type eggs (Horner, 2006).
Mutations in sra do not prevent the fertilization of eggs by sperm; using an antibody that recognizes the sperm tail, the sperm tail was observed in the majority of the eggs produced by mated sra mothers. By examining the sperm nucleus in fertilized sra eggs, it was possible to investigate the interaction between egg activation and maturation of the sperm nucleus into the male pronucleus. In fertilized sra eggs, the sperm nucleus is round, but its diameter is only 1.7 ± 0.04 μm, much smaller than that of fully decondensed male pronuclei seen just prior to pronuclear fusion (Horner, 2006).
To determine if histone exchange occurs in the wild-type sperm nucleus of sra mutant eggs, fertilized laid eggs were stained with propidium iodide for DNA and an antibody that recognizes histone H1, which is not present in mature sperm before fertilization. The sperm nucleus in these eggs is consistently associated with histone H1. Thus, paternal chromosomes associate with histone H1 from maternal stores in sra mutant eggs; it is presumed that H1 targeting requires previous replacement of sperm protamines with the core histones on paternal chromatin (Horner, 2006).
The very first steps of sperm nuclear envelope breakdown, chromosome decondensation, and the replacement of protamines with histones therefore occur in sarah mutant eggs. Sperm produced by males homozygous for the male-sterile gene sneaky cannot undergo these steps even in wild-type eggs. As a result, the DNA of sneaky sperm nuclei in eggs cannot be stained by the membrane-impermeable dye propidium iodide and retains an elongated needle-shaped configuration. In contrast, the sperm nucleus in sarah eggs can be stained by propidium iodide and assumes a rounded shape. Mutations in the sesame gene, which encodes the maternal factor Hira, a histone chaperone required for nucleosome assembly, result in a failure of core histones to incorporate into the sperm nucleus. Sarah-mediated activation events thus appear to be required for neither sneaky nor sesame function; nor do they appear to be required for protamine/histone exchange in general (Horner, 2006).
However, further development of the sperm nucleus does not occur in sra eggs. To determine if the sperm nucleus replicates its genome, laid, fertilized sra mutant eggs were stained for proliferating cell nuclear antigen (PCNA). PCNA functions as a processivity factor of DNA polymerase δ during DNA replication; in early dividing Drosophila embryos, it colocalizes with nuclei during interphase and occasionally in late anaphase or telophase, but never in metaphase. PCNA was never detected on either the sperm nucleus or the anaphase-arrested female nucleus. In wild-type controls, staining was observed on the male and female apposed pronuclei 70% of the time. Sperm nuclei prior to apposition did not stain with PCNA in the wild-type controls (Horner, 2006).
Fertilized eggs for the mitotic marker phosphohistone H3 (Serine 10), which is normally deposited on chromosomes during prophase. Maternally derived chromosomes stained intensely, as expected given their cell-cycle arrest, but the majority of sperm nuclei (n = 8/9) in the same embryos did not stain for phosphohistone H3. Together, these findings indicate that the sperm nuclei are arrested in a pre-S phase, premitotic state in the absence of maternal sra function. Although it may appear paradoxical that the male and female genomes in these eggs are arrested at very different stages of the cell cycle, precedents in sea urchin zygotes indicate that the cell cycles of male and female pronuclei are independently regulated, probably by the differential accumulation of active MPF in the respective nuclei (Horner, 2006).
Fertilized sra eggs were stained for tubulin as well as for DNA to determine whether the sperm nucleus could elaborate the prominent sperm aster along which the female pronucleus migrates to allow pronuclear apposition. The sperm aster is first visible in wild-type zygotes when the female genome is undergoing anaphase II and then grows enormously during telophase II. However, no sperm aster, nor indeed any organized microtubule system associated with sperm nuclei, was observed in sra eggs (Horner, 2006).
Sperm nuclei in sra mutant eggs thus become arrested prior to DNA replication, prophase of the first mitotic division, formation of the sperm aster, and nuclear apposition. The results taken together indicate that sperm nuclear-envelope breakdown, initial chromatin decondensation, and histone exchange are dependent on male-supplied factors such as sneaky and maternal factors including sesame, but these early steps are independent of sarah-mediated egg activation. Later steps in sperm activation do require Sarah and concomitant egg activation (Horner, 2006).
Because injection of nondegradable cyclin B causes early anaphase arrest of syncytial blastoderm mitoses, cyclin B elevation might explain the anaphase I arrest seen in sra mutant embryos. Thus lysates from fertilized, laid eggs of sra mutant females were probed for cyclin B on Western blots. As controls, eggs from wild-type females (fertilized and unfertilized) and sra heterozygotes were also tested, as were activated eggs from cortex mutant mothers that were terminally arrested in metaphase II. Eggs from sra mothers showed an elevation of cyclin B when they were compared to those from sra heterozyogotes and wild-type fertilized eggs. It is presumed that the low levels of cyclin B in the latter embryos result from asynchronous development of the population during the 2 hr collection, so that only a small proportion of embryos are in mitosis. Wild-type unfertilized eggs and cortex eggs showed elevated cyclin B levels similar to those seen in sra mutants, consistent with meiotic arrest. These results likely reflect a role for Sarah as a regulator of M phase-promoting factor (MPF) during egg activation (Horner, 2006).
In vertebrates and marine invertebrates, fertilization triggers a transient rise in free Ca2+, and this rise is responsible for subsequent activation events such as modification of the eggshell, prevention of polyspermy, and cell-cycle resumption. This study shows that a protein involved in a calcium signal-transduction pathway is necessary for several egg-activation events in Drosophila. The sarah gene product is a calcipressin; the human calcipressin DSCR1 can directly bind to and inhibit calcineurin, the only known phosphatase that is dependent on both calcium and calmodulin. The accompanying paper by Takeo (2006) verifies that the fly Sarah protein shares these biochemical properties (Horner, 2006).
The present understanding of egg activation in Xenopus and the activities of calcipressin make strong predictions for the role of sra in meiotic reactivation. Upon fertilization of frog eggs, Ca2+ activates calmodulin-dependent protein kinase II (CaMKII), which in turn directs the inactivation of Anaphase Promoting Complex (APC) inhibitors such as Erp1/Emi2. The APC in turn inactivates MPF through the destruction of cyclin, relieving the meiotic block and initiating other egg-activation events. The current results suggest that essentially the same pathway operates during the activation of Drosophila eggs. It is hypothesized that Sarah acts early in the pathway by mediating the antagonistic relationship between calcineurin and CaMKII; that is, CaMKII activity upon egg activation requires the inhibition of calcineurin by Sarah (Horner, 2006).
Consistent with this model is the similarity of the sarah phenotype to that associated with mutations in another Drosophila gene called cortex. The Cortex protein is a member of the Cdc20 protein family, whose members serve as specificity factors and activators for the APC. Meiosis arrests normally at metaphase I in cortex oocytes and resumes when the eggs are laid but then soon arrests again at metaphase II. The variation in the phase of the meiotic arrest (metaphase II versus anaphase I) being an exception, other aspects of egg activation are similarly affected by mutations in cortex and sra (Horner, 2006).
The meiotic arrest in both sra and cortex eggs is most simply explained by the failure of the APC to target certain molecules for degradation upon egg laying. In cortex eggs, cyclin A fails to be degraded. The cyclin B component of MPF remains undegraded in sra eggs. These results are consistent with the mitotic-arrest phenotypes seen in early Drosophila embryos expressing nondegradable cyclin A (metaphase arrest) or nondegradable cyclin B (early anaphase arrest). Different APC targets could remain undegraded in sra and cortex eggs because there are at least two Cdc20-like proteins (Cortex and Fzy) in Drosophila eggs. APCCortex and APCFzy may have different substrate specificities and may be differently regulated by APC inhibitors downstream of CaMKII (Horner, 2006).
The failure of the eggs laid by sra mutant mothers to translate the maternal bcd mRNA can also be understood in the same theoretical framework. The translation of bcd requires the polyadenylation of its mRNA; the enzyme poly(A) polymerase that catalyzes polyadenylation is phosphorylated and thus negatively regulated by MPF. Failure of APC activation in sra mutant eggs would therefore prevent both MPF inactivation and bcd mRNA translation (Horner, 2006).
Although meiosis and bcd translation are both disrupted in sra eggs, vitelline membrane (VM) cross-linking is apparently normal. VM cross-linking also occurs in other mutants that block female meiotic progression; such mutants include cortex, grauzone, prage, and wispy. In fact, VM reorganization can occur independently of every other known egg-activation event, including bcd mRNA translation, the degradation of other maternal mRNAs, and microtubule depolymerization. If there is only a single trigger for egg activation, it must therefore be able to activate at least two autonomous downstream pathways (one for VM cross-linking and a second for other events). Because in vitro activated eggs are defective in several aspects of embryonic development, it is difficult to interpret the finding of delayed VM modification in sra eggs upon in vitro activation. Although sra function is not formally required for VM organization, sra-dependent processes might nonetheless impinge on its efficiency (Horner, 2006).
In summary, results indicate that despite its independence from a sperm trigger, egg activation in Drosophila involves calcium-mediated pathways that are likely to be analogous to those in other animals. It is intriguing that among these downstream events is the acquisition of the egg's competence to remodel the sperm nucleus into the male pronucleus (Horner, 2006).
To better understand the genetic bases of postmating responses in Drosophila melanogaster females, a collection of P{GS} insertion lines were screened and two insertions in were identified sarah (sra), whose misexpression in the nervous system induced high levels of ovulation in virgins. The gene sra encodes a protein similar to human Down syndrome critical region 1 (DSCR1). The ovulation phenotype was reproduced in transgenic virgins expressing UAS-sra in the nervous system. The flies also extruded the ovipositor toward courting males as seen in wild-type mated females, supporting the notion that ovulation and behavioral patterns are physiologically coupled. The sra insertions were found to be hypomorphic alleles with reduced expression levels. Females homozygous for these alleles show: (1) spontaneous ovulation in virgins, (2) sterility with impaired meiotic progression, and (3) compromised postmating responses with lower ovulation level, higher remating rate, and shorter period for restoration of receptivity. No obvious defects were observed in the homozygous males. The gene sra is predominantly expressed in oocytes, nurse cells, and the nervous system. Taken together, these results indicate that the expression level of sra is critical for ovulation and female courtship behavior, including their postmating changes (Ejima, 2004; full text of paper).
Mental retardation is the most common phenotypic abnormality seen in Down syndrome (DS) patients, yet the underlying mechanism remains mysterious. DS critical region 1 (DSCR1), located on chromosome 21, is overexpressed in the brain of DS fetus and encodes an inhibitor of calcineurin, but its physiological significance is unknown. To study its functional importance and role in mental retardation in DS, Drosophila mutants of nebula, an ortholog of human DSCR1, were generated. Both nebula loss-of-function and overexpression mutants exhibit severe learning defects that are attributed by biochemical perturbations rather than maldevelopment of the brain. These results, combined with data showing that the same biochemical signaling pathway is altered in human DS fetal brain tissue overexpressing DSCR1, suggest that alteration of DSCR1 expression could contribute to mental retardation in DS (Chang, 2003; full text of article).
To investigate the role of nebula in learning and memory, a Pavlovian olfactory associative learning and memory test was used. Significant defect in learning was observed after a single trial of training for homozygous nla1 and nla2 mutants, as compared to nla1 heterozygotes, precise excision line (nlaPJ), and CS flies. The learning defects are not attributed by abnormal sensorimotor responses, because both odor and shock avoidances were indistinguishable among the fly lines tested. Nevertheless, the possibility that some of the performance defects seen in the nebula mutants could be caused by subtle alteration in sensitivity to stimuli cannot be ruled out (Chang, 2003).
Short-term memory is thought to last 60 min after training in Drosophila. Thus short-term memory was investigated in different nebula alleles by examining the performance at different time points after training. The same rate of normal memory decay seen for the different fly lines suggests that short-term memory is likely intact and that the low performance value obtained right after training may be a reflection of defective learning, albeit the possibility cannot be ruled out that nebula is required for immediate short-term memory (during the 3 min in between training and the first possible test time point). To further examine the role of nebula in the memory pathway, long-term memory was tested in the nebula mutants. Long-term memory in Drosophila is associated with phosphorylated cAMP-responsive element binding protein (pCREB) and protein synthesis and is evident 1 day after 10 trials of spaced training with 15-min rest intervals between trainings. Strikingly, it was found that homozygous nebula mutants showed a virtual absence of long-term memory, whereas control flies displayed ~40% memory retention 24 h after training. The observed defect in long-term memory is not caused by the initial deficiency in acquisition, because the performance of nla1 and nla2 homozygotes immediately after spaced training did not differ significantly from CS flies. Together, these results indicate that increasing the number of training sessions can improve the learning performance of nebula mutants, and more importantly, nebula is required for effective learning and long-term memory (Chang, 2003).
Despite the overall normal brain structure, it is possible that the learning and memory deficits seen for the nebula mutants are caused by structural defects specifically in the mushroom bodies, the center for learning and memory in Drosophila. To examine the integrity of the mushroom bodies, the α, β, and γ lobes were visualized with Fasciclin II antibody. Of all 60 nla1 homozygous mutant flies examined, no visible structural defect in the mushroom bodies was detected, and the α, β, and γ lobes were similar to the control flies. This finding implies that the nebula mutation does not cause maldevelopment of the mushroom bodies and that defects in learning and memory are not caused by gross structural defect (Chang, 2003).
To understand whether the mutation in nebula significantly alters the biochemical activity predicted for the gene, calcineurin activity level was examined in the nebula mutant flies. Calcineurin activity detected in the homogenate of nla1 homozygotes was ~40% higher than CS control and nla1 heterozygotes, indicating that nebula functions as an endogeneous inhibitor of calcineurin as other members in the calcipressin family. The signaling pathways downstream from calcineurin was examined and it was found that homozygous nla1 mutants showed a substantial decrease in cAMP-dependent protein kinase (PKA) activity, the amount of pCREB, and the level of d-jun transcripts. Given that PKA and pCREB are important for normal learning and long-term memory, the observed biochemical perturbations in the nebula mutant may contribute to the observed deficiency in learning and memory (Chang, 2003).
By using Drosophila as a simple model organism, this study demonstrated that nebula mediates learning and long-term memory. Observations that both nebula loss-of-function and overexpression mutants displayed learning defects suggest that precise regulation of nebula-mediated calcineurin signaling is necessary to maintain optimum learning. Furthermore, these results, along with data that the same biochemical pathway is disrupted in human trisomy 21 fetal brain tissue, strongly implicate the involvement of DSCR1 in mental retardation in DS (Chang, 2003).
This study focused on the function of DSCR1 in learning and memory to address its role in mental retardation associated with DS. However, DSCR1 is also expressed in other tissues such as the heart and skeletal muscle and may thus regulate diverse calcineurin-dependent processes. Furthermore, calcineurin has been shown to regulate the transcription of DSCR1, suggesting the existence of a complex negative feedback regulation circuit. It will be interesting to investigate whether such regulatory mechanism also controls nebula expression in flies. Combined with its amenability to genetic manipulations and behavioral assays, Drosophila can be used to identify some of the genotype-phenotype relations in DS. In addition, the finding that defective learning in nebula overexpressing flies is likely caused by functional defects rather than developmental defects raises the exciting possibility of pharmacological intervention to ameliorate at least some of the cognitive deficits in DS patients. Drosophila may be used as a tool to rapidly screen for drugs that treat learning and memory deficits by restoring the balance of kinases and phosphatases. Genetic screens that identify suppressors of nebula in the learning and memory pathway will also provide insights into the underlying mechanism of mental retardation in DS (Chang, 2003).
Mitochondrial dysfunction has emerged as a common theme that underlies numerous neurological disorders, including Down syndrome. Down syndrome cultures and tissues show mitochondrial damage such as impaired mitochondrial enzyme activities, defective mitochondrial DNA repairs and accumulation of toxic free radicals, but the cause of mitochondrial dysfunction remains elusive. This study demonstrated that the Drosophila melanogaster homolog of human Down syndrome critical region gene 1 (DSCR1), nebula (also known as sarah, sra), has a crucial role in the maintenance of mitochondrial function and integrity. nebula protein is located in the mitochondria. An alteration in the abundance of nebula affects mitochondrialenzyme activities, mitochondrial DNA content, and the number and size of mitochondria. Furthermore, nebula interacts with the ADP/ATP translocator and influences its activity. These results identify nebula/DSCR1 as a regulator of mitochondrial function and integrity and further suggest that an increased level of DSCR1 may contribute to the mitochondrial dysfunction seen in Down syndrome (Chang, 2005).
Reference names in red indicate recommended papers.
Search PubMed for articles about Drosophila Sarah
Arron, J. R., et al. (2006). NFAT dysregulation by increased dosage of DSCR1 and DYRK1A on chromosome 21. Nature 441(7093): 595-600. Medline abstract: 16554754
Aubareda, A., Mulero, M. C. and Perez-Riba, M. (2006). Functional characterization of the calcipressin 1 motif that suppresses calcineurin-mediated NFAT-dependent cytokine gene expression in human T cells. Cell Signal 18(9): 1430-8. Medline abstract: 16406492
Cano, E., Canellada, A., Minami, T., Iglesias, T. and Redondo, J. M. (2005). Depolarization of neural cells induces transcription of the Down syndrome critical region 1 isoform 4 via a calcineurin/nuclear factor of activated T cells-dependent pathway. J. Biol. Chem. 280(33): 29435-43. Medline abstract: 15975916
Casas, C., et al. (2001). Dscr1, a novel endogenous inhibitor of calcineurin signaling, is expressed in the primitive ventricle of the heart and during neurogenesis. Mech. Dev. 101(1-2): 289-92. Medline abstract: 11231093
Chan, B., Greenan, G., McKeon, F. and Ellenberger, T. (2005). Identification of a peptide fragment of DSCR1 that competitively inhibits calcineurin activity in vitro and in vivo. Proc. Natl. Acad. Sci. 102(37): 13075-80. Medline abstract: 16131541
Chang, K. T., Shi, Y. J., Min, K. T. (2003). The Drosophila homolog of Down's syndrome critical region 1 gene regulates learning: implications for mental retardation. Proc. Natl. Acad. Sci. 100(26): 15794-9. Medline abstract: 14668437
Chang, K. T. and Min, K. T. (2005). Drosophila melanogaster homolog of Down syndrome critical region 1 is critical for mitochondrial function. Nat. Neurosci. 8(11): 1577-85. Medline abstract: 16222229
Ejima, A., Tsuda, M., Takeo, S., Ishii, K., Matsuo, T. and Aigaki, T. (2004). Expression level of sarah, a homolog of DSCR1, is critical for ovulation and female courtship behavior in Drosophila melanogaster. Genetics 168(4): 2077-87. Medline abstract: 15611177
Ermak, G., Morgan, T. E. and Davies, K. J. (2001). Chronic overexpression of the calcineurin inhibitory gene DSCR1 (Adapt78) is associated with Alzheimer's disease. J. Biol. Chem. 276(42): 38787-94. Medline abstract: 11483593
Ermak, G., Harris, C. D. and Davies, K. J. (2002). The DSCR1 (Adapt78) isoform 1 protein calcipressin 1 inhibits calcineurin and protects against acute calcium-mediated stress damage, including transient oxidative stress. FASEB J. 16(8): 814-24. Medline abstract: 12039863
Ermak, G., Harris, C. D., Battocchio, D. and Davies, K. J. (2006). RCAN1 (DSCR1 or Adapt78) stimulates expression of GSK-3beta. FEBS J. 273(10): 2100-9. Medline abstract: 16649988
Fuentes, J. J., et al. (2000). DSCR1, overexpressed in Down syndrome, is an inhibitor of calcineurin-mediated signaling pathways. Hum. Mol. Genet. 9: 1681-1690. Medline abstract: 10861295
Gajewski, J., et al. (2003). Requirement of the calcineurin subunit gene canB2 for indirect flight muscle formation in Drosophila. Proc. Natl. Acad. Sci. 100: 1040-1045. Medline abstract: 12538857
Genesca, L., et al. (2003). Phosphorylation of calcipressin 1 increases its ability to inhibit calcineurin and decreases calcipressin half-life. Biochem J. 374(Pt 2): 567-75. Medline abstract: 12809556
Gorlach, J., et al. (2000). Identification and characterization of a highly conserved calcineurin binding protein, CBP1/calcipressin, in Cryptococcus neoformans. EMBO J. 19(14): 3618-29. Medline abstract: 10899116
Horner, V. L., et al. (2006). The Drosophila calcipressin Sarah is required for several aspects of egg activation. Curr. Biol. 16(14): 1441-6. Medline abstract: 16860744
Iizuka, M., et al. (2004). Down syndrome candidate region 1, a downstream target of VEGF, participates in endothelial cell migration and angiogenesis. J. Vasc. Res. 41(4): 334-44. Medline abstract: 15263820
Kingsbury, T. J. and Cunningham, K. W. (2000). A conserved family of calcineurin regulators. Genes Dev. 14: 1595-1604. Medline abstract: 20347037
Lange, A. W., Molkentin, J. D. and Yutzey, K. E. (2004). DSCR1 gene expression is dependent on NFATc1 during cardiac valve formation and colocalizes with anomalous organ development in trisomy 16 mice. Dev. Biol. 266(2): 346-60. Medline abstract: 14738882
Lee, J. I., et al. (2003). The Caenorhabditis elegans homologue of down syndrome critical region 1, RCN-1, inhibits multiple functions of the phosphatase calcineurin. J. Mol. Biol. 328: 147-156. Medline abstract: 12684004
Mammucari, C., et al. (2005). Integration of Notch 1 and calcineurin/NFAT signaling pathways in keratinocyte growth and differentiation control. Dev. Cell 8(5): 665-76. Medline abstract: 15866158
Qin, L., et al. (2006). Down syndrome candidate region 1 isoform 1 mediates angiogenesis through the calcineurin-NFAT pathway. Mol. Cancer Res. 4(11): 811-20. Medline abstract: 17114339
Ryeom, S., Greenwald, R. J., Sharpe, A. H. and McKeon, F. (2003). The threshold pattern of calcineurin-dependent gene expression is altered by loss of the endogenous inhibitor calcipressin. Nat. Immunol. 4(9): 874-81. Medline abstract: 12925851
Strippoli, P., et al. (2000). The murine DSCR1-like (Down syndrome candidate region 1) gene family: conserved synteny with the human orthologous genes. Gene 257: 223-232. Medline abstract: 11080588
Sullivan, K. M. C. and Rubin, G. M. (2002). The Ca2+-calmodulin-activated protein phosphatase calcineurin negatively regulates Egf receptor signaling in Drosophila development. Genetics 161: 183-193. Medline abstract: 12019233
Takeo, S., Tsuda, M., Akahori, S., Matsuo, T. and Aigaki, T. (2006). The calcineurin regulator Sra plays an essential role in female meiosis in Drosophila. Curr. Biol. 16(14): 1435-40. Medline abstract: 16860743
date revised: 6 February 2007
Home page: The Interactive Fly © 2006 Thomas Brody, Ph.D.
The Interactive Fly resides on the
Society for Developmental Biology's Web server.