Interactive Fly, Drosophila

Maternally derived Calmodulin mRNA is homogeneously distributed throughout the early Drosophila embryo, but these maternal transcripts are lost by maximal germ band extension. Zygotic transcription of the gene in mid- to late-stage embryos is restricted to neural cell precursors and their progeny in both the central and peripheral nervous systems. Although all neuroblasts express CaM mRNA, certain neuroblasts within each hemisegment show distinctly higher levels than others. The pattern of differential expression is the same for all hemisegments, from cephalic segment two to abdominal segment eight. For each of these hemisegments, all four of the neuroblasts in the outer, lateral row express higher Calmodulin transcript levels. The third and fourth neuroblasts of the inner, medial row also have higher expression level, as does one neuroblast within the intermediate row. Axon tracts of the commissures and connectives are very lightly stained. Three pairs of neurons within the ventral nerve cord have markedly higher levels of CaM mRNA than other neurons. These cells may be some of the paired midline neurons within three of the abdominal segments. All sensory neurons of the Peripheral nervous system express CaM, whereas none of the support cells do. Transcript levels are lower in precursor cells than in differentiated neurons. Activation of Calmodulin transcription during embryonic development appears to mark a commitment to a neural fate. The two transcripts from the Calmodulin gene are differentially expressed during embryogenesis. The longer Calmodulin mRNA is a nervous tissue-specific transcript. This suggests that neural-specific regulation of polyadenylation site usage occurs (Kovalick, 1992).

Calmodulin is present in all cells at all times. In addition to this constitutive level, the amount of Calmodulin is highly regulated according to the tissue or stage of development. The combined level of the transcripts is developmentally regulated, and the relative amounts of the two transcript size classes (1.65 kb and 1.9 kb) are differentially regulated during development. The spatial distribution of Calmodulin transcripts has been examined by in situ hybridization in sections of adults and developmentally staged whole mount embryos. Calmodulin transcripts are evenly distributed early in embryogenesis. The region of the developing midgut is labeled. Stage 15 embryos show sharper anterior localization of label associated with the developing anterior sensory organs. A relatively high level of Calmodulin transcripts can also be seen in the brain. In late stages of embryogenesis, high levels accumulate in the developing nerve cord (Hanson-Painton, 1992).

The expression of the Drosophila calmodulin (CAM) gene is surprisingly complex. The nervous system, which shows intense transcription in embryogenesis, contains no detectable transcripts at the end of larval life, with the exception of expression in the ring gland in the third instar larval stage. New expression takes place at pupariation. This activation occurs at the time of a known burst of ecdysone secretion and is therefore a candidate for a relatively direct hormonal effect. From the mid-pupal stages, regional differences in hybridization intensity are detectable throughout the CNS. Most noticeable, neurons in the brain cortex show stronger hybridization than those in the optic lobes. In addition, marked cell-to-cell variation in hybridization is seen in the central brain, presumably reflecting functional differences between neurons. The gut shows no expression in early embryogenesis, but high levels of expression throughout the larval stages, but none during pupal reorganization. In particular, hybridization to the proventriculus and middle midgut is very intense. The pharyngeal epithelium and salivary glands also show strong expression, with the gastric caecae and anterior midgut showing somewhat lower levels and the Malpighian tubules containing only moderate transcription levels. In contrast, CAM expression in the thoracic muscles drops significantly on transition from pupal to adult life. In the testis, transcription is strongly up-regulated prior to meiosis. In the ovary, strong expression is seen in the nurse cells with even more intense expression in the columnar follicle cells encasing the oocyte. Levels of expression in the oocyte cytoplasm are lower than in the nurse and follicle cells. Growing cells show lower transcript levels than most differentiated tissues and in general, cells with intense exocytotic or endocytotic activity show the highest mRNA levels (Andruss, 1997).

Larval

Seventy-six genes have been identified that are strongly expressed in the Drosophila ring gland during development. For nine of these, further studies of expression pattern, mutant phenotype and molecular nature identify the genes as strong candidates to carry out an important role in endocrine functions controlling development. Two of the genes identified encode products that have already been implicated in the functioning of prothoracic glands in other insects. The Calmodulin gene is expressed exclusively and at high levels in the ring gland of third-instar larvae, suggesting an important, presumably endocrine function for calmodulin in that tissue, as has already been suggested for lepidopterans. Calmodulin and other Ca²⁺-binding proteins are integral to the transduction of a wide range of Ca²⁺-dependent signals; there is clear evidence for the Ca²⁺ dependence of ecdysteroid molting hormone (EC) production in the Manduca larval prothoracic gland (PTG), at least for the commitment peak early in the last larval instar. It is known that Ca²⁺ activates prothoracic gland adenylate cyclase both directly and as a complex when bound to calmodulin. Since cAMP phosphodiesterase activity is low at this stage, cAMP is expected to accumulate. Both large and small PTTHs (see Bombyx and Manduca prothoracicotropic hormone) stimulate increased cAMP levels in PTG; a rise in cAMP levels occurs with PTTH-stimulated EC production in early last-instar PTG (Harvie, 1998 and references).

The catalytic subunit of protein kinase A (PKA or cAMP-PK) is also expressed in the Drosophila ring gland. This protein probably functions downstream of cAMP in the Ca²⁺-cAMP-dependent signaling pathway. PKA is activated in M. sexta PTGs by PTTH immediately prior to EC production. This is consistent with the idea that activation of the Ca²⁺-cAMP-dependent signaling pathway by PTTH leads to PKA-dependent phosphorylation of key proteins, including ribosomal protein S6, and that this causes changes in selective translation leading to increased EC production (Harvie, 1998 and references).

Adult

The vast majority of ovarian Calmodulin mRNA species are of the shorter type (Kovalick, 1992).

Elevated levels of Calmodulin transcripts are seen quite distinctly in the adult neural tissues. Accumulation is quite high in the cell bodies surrounding the lamina, the medulla, and the lobula, as well as the cell bodies of the subesophageal ganglion, the mass of neurons providing communication from the head organs to the rest of the neurons extending into the thorax. In the compound eye, the striations in the grain distribution follow the length of the ommatidia. The observed pattern suggests that different cells of the ommatidia accrue different amounts of Calmodulin transcript (Hanson-Painton, 1992).

Effects of Mutation or Deletion

Targeted disruption of Ca(2+)-Calmodulin signaling in Drosophila growth cones leads to stalls in axon extension and errors in axon guidance. Ca(2+)-Calmodulin (CaM) function is selectively disrupted in a specific subset of growth cones in transgenic Drosophila embryos in which a specific enhancer element drives the expression of the kinesin motor domain fused to a CaM antagonist peptide (kinesin-antagonist or KA, which blocks CaM binding to target proteins) or CaM itself (kinesin-CaM or KC, which acts as a Ca(2+)-binding protein). In both KA and KC mutant embryos, specific growth cones exhibit dosage-dependent stalls in axon extension and errors in axon guidance, including both defects in fasciculation and abnormal crossings of the midline. These results demonstrate an in vivo function for Ca(2+)-CaM signaling in growth cone extension and guidance and suggest that Ca(2+)-CaM may in part regulate specific growth cone decisions, including when to defasciculate and whether or not to cross the midline (Van Berkum, 1995).

The establishment of axon trajectories is ultimately determined by the integration of intracellular signaling pathways. Here, a genetic approach in Drosophila has demonstrated that both Calmodulin and Son of sevenless signaling pathways are used to regulate which axons cross the midline. A loss in either signaling pathway leads to abnormal projection of axons across the midline and these increase with roundabout or slit mutations. When both Calmodulin and Son of sevenless are disrupted, the midline crossing of axons mimics that seen in roundabout mutants, although Roundabout remains expressed on crossing axons. Calmodulin and Son of sevenless also regulate axon crossing in a commissureless mutant. These data suggest that Calmodulin and Son of sevenless signaling pathways function to interpret midline repulsive cues that prevent axons crossing the midline (Fritz, 2000).

A novel CaM inhibitor, called kinesin-antagonist (KA), has been expressed using the neurogenic enhancer element of the fushi tarazu gene (ftzng) in a subset of CNS neurons that normally do not cross the midline. KA expression decreases endogenous CaM activation of target proteins in the growth cone and this leads to specific axon guidance defects including stalls at selected choice points, failure to fasciculate properly and abnormal crossing of the midline. robo and slit mutations and KA interact synergistically to increase the number of axon bundles abnormally crossing the midline. KA also induces axon bundles to cross the midline in the absence of Comm protein. Sos-dependent crossovers are enhanced by KA or by slit mutation. KA and Sos also interact to increase the number of axon bundles crossing in a comm mutant. Thus, the data demonstrate that both CaM and Sos signaling pathways are required to prevent certain axons crossing the midline (Fritz, 2000).

Whether CaM and Sos-mediated signaling is working directly downstream of Robo or in closely associated, but parallel signaling pathways to prevent axons from crossing is difficult to ascertain from this genetic data alone. If these signaling pathways lie downstream of Robo, the data suggest that both CaM and Sos are activated upon Slit binding to Robo, and result in growth cone repulsion. Interestingly, increased levels of calcium have been implicated in growth cone retraction and growth cone collapse, two ways in which a growth cone may respond to a repulsive agent. In addition, retrograde actin flow, which leads to filopodial retraction, is stimulated by CaM activation of myosin light chain kinase. Two other CaM target proteins, cAMP adenylyl cyclase and phosphodiesterase, regulate cAMP cellular concentrations thus altering neuronal response to Netrin 1 and other guidance cues. Activation of a Sos signaling pathway can affect cytoskeletal dynamics by activating various GTPases known to regulate growth cone behavior and axon guidance. Moreover, the cytoplasmic tail of Robo, known to be essential for signaling function, has a tyrosine residue that could recruit Sos via Drk or dreadlocks (dock), another SH2-SH3 adapter protein that affects axon guidance. Alternatively, Robo may bind Enabled, a known substrate for Abelson tyrosine kinase (Abl), which has been implicated in commissure formation. If Sos binds to phosphotyrosine residues on Ena (also via an adapter protein) it could be indirectly recruited to Robo (Fritz, 2000 and references therein).

Another possibility is that a disruption in both the CaM and Sos signaling pathways indirectly causes abnormal crossovers. CaM has been identified as a player downstream of several guidance molecules. Indeed, the gaps in the longitudinal connectives observed with increasing copies of KA in a comm mutant or in KA robo mutants, which are not seen in robo mutants alone, suggest CaM may function downstream of other guidance cue receptors to allow extension through the connective. Once these signals are attenuated by expression of KA, axons may inadvertently cross the midline. However, if CaM only functions in cell adhesive mechanisms within the connectives, it is difficult to explain why axons cross the midline in comm mutants when no other axons cross and the presence of Slit is still being read by Robo (Fritz, 2000 and references therein).

Since CaM and Sos appear to interpret a midline repulsive cue, the existence of an additional midline repulsion system working in parallel to Robo represents an interesting possibility. In robo mutants, axons cross the midline but then move to the longitudinal connective, instead of collapsing at the midline as observed in slit mutants. It has been suggested that this occurs because the continued presence of Slit at the midline is detected by a second receptor system, and candidate genes include a second robo gene or karussel. As the data shows, heterozygous slit mutations interact very strongly with single copies of KA, Sos or KA Sos together, to force axons across the midline. The interaction between Sos and slit mutations, especially when compared to the lack of Sos and robo interaction, is particularly striking. It seems that if the activity of both repulsion systems is decreased due to the reduction of a common ligand (Slit), a disruption in CaM and/or Sos signaling dramatically increases midline crossing errors. Most of these results, including the synergistic effects of KA and Sos, robo and slit mutations, the robo-like phenotype of KA Sos mutants, and the enhancement of crossovers in comm mutants can be explained by a parallel decrease in both midline repulsive systems upon disruption of the CaM and Sos signaling pathways. Thus while the mechanisms by which CaM and Sos contribute to an axon guidance decision at the midline remain unclear, the data clearly indicate that CaM and Sos signaling pathways are critical to the transduction of repulsive information at the midline (Fritz, 2000 and references therein).

Three systems are involved in Drosophila phototransduction and there are two messengers for Drosophila light excitation. InsP3, generated by phospholipase C, could function as the first messenger, acting to trigger the amplification of the light signal by causing the release of Ca2+ from the endoplasmic reticulum via the ryanodine receptor. Thus InsP3 based amplification is the first system. Ca2+, in turn, acts as a second messenger by acting to engender its own release. This function of calcium serves as the second system activated in the photosynthetic cascade. Calmodulin is involved in regulating Ca2+ stores in Drosophila, inactivating the response, and thus acting as the third system involved in the photosynthetic cascade. Treatment of Drosphila photoreceptor cells with ryanodine and caffeine disrupt the current induced by light, whereas subsequent application of calcium-calmodulin (Ca-CaM) rescues the inactivated photoresponse. In calcium-deprived wild-type Drosophila and in calmodulin-deficient transgenic flies, the current induced by light is disrupted by a specific inhibitor of Ca-CaM. Furthermore, inhibition of Ca-CaM reveals light-induced release of Ca2+ from intracellular stores. Thus it appears that functional ryanodine-sensitive stores are essential for photoresponse. Calcium release from these stores appears to be a component of Drosophila phototransduction, and Ca-CaM regulates this process (Arnon, 1997b).

The regulatory protein Calmodulin is a major mediator of calcium-induced changes in cellular activity. To analyze the roles of Calmodulin in an intact animal, a Calmodulin null mutation was generated. Maternal Calmodulin supports Calmodulin null individuals throughout embryogenesis, but they die within 2 days of hatching as first instar larvae. Two pronounced behavioral abnormalities specific to the loss of Calmodulin are detected in these larvae: swinging the head and anterior body, which normally occurs in the presence of food, is three times more frequent in the null animals. Even more striking, most locomotion in Calmodulin null larvae is spontaneous backward movement. This is in marked contrast to the wild-type situation where backward locomotion is seen only as a stimulus-elicited avoidance response. The finding of spontaneous avoidance behavior has striking similarities to the enhanced avoidance responses produced by some Calmodulin mutations in Paramecium. Thus these results suggest evolutionary conservation of a role for Calmodulin in membrane excitability and linked behavioral responses (Heiman, 1996).

Calmodulin (CAM) is recognized as a major intermediary in intracellular calcium signaling, but as yet little is known of its role in developmental and behavioral processes. Mutations to the endogenous Cam gene of Drosophila melanogaster that change single amino acids within the protein coding region were generated and studied. One of these mutations (Cam7) produces a striking pupal lethal phenotype involving failure of head eversion. Cam7 mutants have smaller pupal cases than normal, with a distinctive "Michelin-man" phenotype of deeply indented rings corresponding to the junctions of larval body segments. Various mutant combinations produce specific patterns of ectopic wing vein formation or melanotic scabs on the cuticle. It is suggested that this head eversion phenotype reflects specific disruption of an interaction of Cam with Myosin light chain kinase (MLCK). The wing vein phenotype indicates a role for Cam in suppression of vein formation. coracle, a Drosophila homolog of the mammalian Protein 4.1, a component of the plasma membrane cytoskeleton and a known Cam binding protein in vertebrates, could be involved in the wing vein phenotype. Anaphase chromosome bridging is also seen as a maternal effect during the early embryonic nuclear divisions. In addition, specific behavioral defects such as poor climbing and flightlessness are detected among these mutants. Comparisons with other Drosophila mutant phenotypes suggests potential CAM targets that may mediate these developmental and behavioral effects, and analysis of the CAM crystal structure suggests the structural consequences of the individual mutations (Nelson, 1997).

Mutations have been generated in the single Drosophila Calmodulin gene and the effects of these mutations then examined on behavior, synaptic transmission at the larval neuromuscular junction, and structure of the larval motor nerve terminal. Flies hemizygous for Cam^3c1, a mutation in the first Ca2+-binding site, exhibit behavioral, neurophysiological, and neuroanatomical abnormalities. In particular, adults exhibit defects in locomotion, coordination, and flight. The effects on motor neuron function and transmitter release of many behavioral mutations, particularly those affecting ion channels, are enhanced by application of the K+ channel-blocking drug quinidine. This drug, when applied at a concentration of 0.1 mM, completely and specifically blocks the delayed rectifier K+current in the Drosophila larval muscle. Application of quinidine enhances the effects of ion channel mutations, such as Shaker and Hyperkinetic, on the duration of motor nerve terminal depolarization and transmitter release. The phenotypes of other excitability mutants, such as inebriated and pushover, are also enhanced by quinidine application. Application of quinidine has no significant effect on excitatory junctional current (EJC) amplitude in the wild-type control larvae or in larvae heterozygous for Cam mutations. In contrast, quinidine application to Cam^3c1/Cam^null at the three lowest external [Ca2+] levels tested causes an approximately threefold increase in EJC amplitude. The muscle responsiveness to neurotransmitter is shown to be normal, and that the increased amplitude EJCs observed in Cam^3c1/Cam^null larvae reflect increased transmitter release. One might imagine that impaired activation of a K+ channel in Cam^3c1/Cam^null might have no observable phenotypic consequences under otherwise normal conditions; however, in combination with quinidine, which could block a distinct, functionally redundant K+ channel, this effect could lead to increased nerve terminal depolarization and increased Ca2+ influx into the nerve terminal. The observation that the effects of Cam^3c1/Cam^null occur only at low external [Ca2+] is consistent with this view: the effects of most excitability mutations, including Shaker, Hyperkinetic, and inebriated, are also revealed only at low external [Ca2+]. This observation has been proposed to result from the activation of a Ca2+-activated K+ current at higher external [Ca2+]. Alternatively, Cam^3c1/Cam^null could be defective in Ca2+ buffering. In this view, a broadening of the action potential conferred by quinidine application combined with reduced Ca2+ buffering as a consequence of Cam3c1/Camnull could lead to increased transmitter release (Arredondo, 1998).

Synaptic bouton structure at motor nerve terminals is altered. Structural abnormalities are present in the nerve terminals of Cam^3c1/Cam^null larvae in muscle 13 of abdominal segments 3 - 5. In particular, rather than cascading into a string of distinct type I and II boutons as in the control larvae, the terminal arbor of the Cam^3c1/Cam^null larvae forms a thickened, or large, misshapen structure with few distinct boutons. The large structure results in a reduced number of boutons and a nearly complete lack of terminal branching in muscle 13. In comparison to control larvae, no abnormalities in the structure of nerve terminals on muscles 6, 7, or 12 have been observed. Despite this altered synapse morphology, muscle 13 synaptic transmission in Cam^3c1/Cam^null larvae resembles the muscle 6 properties. This observation raises the possibility that this defective bouton might still be functional. Although mutations in several neuronal signaling genes confer defects in the pattern of motor neuron innervation of the target muscle, the morphological defects of Cam^3c1/Cam^null at the nerve terminal differ from any that have been reported previously and do not appear to result from the same mechanisms as the "activity-dependent" increases in synaptic bouton number or axonal branching Rather, the phenotype observed appears to result from defects in the formation of distinct boutons at the proper locations along the muscle surface. It is unclear why this defect in bouton formation is observed only in muscle 13. Proper synapse formation on muscle 13 may be more sensitive to altered CaM function, or perhaps distinct mechanisms control bouton formation in muscle 13 vs. other muscles. Analysis of the genes required for proper bouton formation is less characterized than for axon pathfinding or growth cone guidance. The results presented here suggest a role for CaM in this process (Arredondo, 1998).

These effects are distinct from those produced by altering the activity of the CaM target enzymes CaM-activated kinase II (CaMKII) and CaM-activated adenylyl cyclase (CaMAC or Rutabaga). Mutations in rutabaga reduce facilitation and post-tetanic potentiation at the larval neuromuscular junction, whereas activation of an inhibitory domain of CaMKII confers a number of behavioral, electrophysiological, and anatomical defects, including defects in courtship conditioning, an abnormal spontaneous firing of motor axon action potentials, increases in axon branching and transmitter release, and a reduction in facilitation and augmentation. Cam3c1/Camnull larvae do not show these phenotypes; e.g., Cam^3c1/Cam^null larvae possess a normal number of axon branches and display normal EJC amplitude (in the absence of quinidine) and normal paired pulse facilitation. Similarly, whereas application of quinidine to Cam^3c1/Cam^null substantially increases evoked transmitter release, quinidine application has little or no effect on CaMKII-inhibited larvae. Thus, it is unlikely that the Cam^3c1 mutation is exerting its effects via either CaMAC or CaMKII, but rather via an alternative target. One alternative target, the Drosophila CaM-activated protein kinase Caki, is expressed in the central nervous system; mutants defective in caki exhibit behavioral defects related to those described here (Martin, 1996). The catalytic domain of Caki shares homology (41%) with type II CaM kinases, while the C-terminal part is divergent. Constitutively expressed Caki protein is enzymatically active. In situ hybridization shows that during embryogenesis, larval and pupal life, transcription of caki is restricted almost exclusively to the central nervous system. In the adult head, immunohistochemistry reveals Caki protein in the lamina, the neuropil of the medulla, lobula, lobula plate and in the central brain. Mutant caki flies show reduced walking speed in 'Buridan's paradigm'. Thus, the Cam^3c1 mutation might affect Ca2+ buffering or interfere with the activation or inhibition of a CaM target, distinct from CaMKII or CaMAC (Arredondo, 1998).

Working with mutants for two calcium binding sites, a study to assess the ability of Drosophila Calmodulin to form complexes with model target peptides melittin and mastoparan has shown that unlike the wild-type complex, the 1:1 protein:melittin complexes formed by mutants of the C-terminal sites are unable to bind a second molecule of melittin. In contrast, a site 2 mutant shows increased ability to bind two molecules of melittin. For the shorter peptide mastoparan, most mutants form aberrant complexes that are best interpreted in terms of a model in which mastoparan interacts with both terminal domains of Calmodulin. For two of the target enzymes of Calmodulin, the three mutants which form mastoparan complexes most similar to the wild-type complex are also the best enzyme activators (Mukherjeam, 1993).

The kinetics of calcium dissociation from two groups of site-specific mutants of Calmodulin from Drosophila have been studied by stopped-flow kinetic methods, using the fluorescent calcium chelator Quin 2. The BQ series of mutants consists of four proteins in which one of the four bidentate glutamate residues (Glu12 of each of the four calcium binding loops) has been replaced by glutamine. In the BK series of mutants, the corresponding glutamate has been replaced by lysine. Calcium-dissociation kinetics of proteins with a mutation in site I or II (N-terminal domain) are consistent with a model in which the mutation weakens binding at the non-mutated N-terminal partner site and has a small, but significant, effect on the kinetic properties of sites III and IV (C-terminal domain). The proteins with a mutation in site III or IV show a large effect, with decreased Ca2+ dissociation rate from the unmodified N-terminal Ca(2+)-binding sites I and II. A structural interpretation has been proposed, based on enhanced interactions between the domains when the affinity of individual sites have been dramatically reduced by mutation. This effect is greatest for the mutations in the C-terminal domain, which appear to destroy the co-operativity of Ca2+ binding at sites III and IV. The results show that site-specific mutation can have surprisingly far-ranging effects on kinetic properties of Calmodulin. The kinetic analysis also shows that studies of specifically engineered mutants may in principle help to unmask the values of intrinsic rate constants for the wild-type protein, not normally observable in the process of Ca2+ dissociation (Martin, 1992).

Ca2+ binding to the wild-type protein is best modeled as two pairs of sites with a higher affinity pair that shows strong cooperativity. For all but one of eight mutant proteins, only three Ca(2+)-binding events can be detected. In three of the amino-terminal mutants, the three residual sites are (i) a pair of relatively high affinity sites and (ii) a weakened low affinity site. For all four carboxyl-terminal mutations, the residual sites are three relatively low affinity sites. In general, mutations to sites 2 and 4 prove more deleterious than mutations to sites 1 and 3. The Ca(2+)-induced conformational changes in the vicinity of Tyr-138 are relatively undisturbed by mutations of site 1. However, the changes to Tyr-138 in the carboxyl-terminal site mutants indicate that upon disruption of the cooperative binding at the high affinity sites, conformational change in the carboxyl terminus occurs in two phases. It appears that binding of Ca2+ to either carboxyl-terminal site can elicit the first phase of the response but the second phase is almost abolished when site 4 is the mutated site. The final conformations of site 3 and 4 mutants are thus significantly different (Maune, 1992a).

In the absence of Ca2+, the helical content of these mutant Calmodulins is close to that of the wild-type protein. In the presence of excess Ca2+, Calmodulins with a mutation in the N-terminal sites show Ca(2+)-induced increases in helicity that are similar to those of the wild-type protein. In contrast, much less additional helix is induced by Ca2+ in Calmodulins with mutations in the C-terminal sites, with the two mutations to site IV showing a particularly poor response. Ca(2+)-induced changes to the environment of the single tyrosine of Drosophila Calmodulin (Tyr-138 in site IV of the C-terminal domain) have been monitored via CD at 280 nm. The signal from this residue is significantly altered in the Ca(2+)-free form of almost all these mutants, including those in the N-terminal domain. This indicates significant interaction between the N- and C-terminal domains of these mutants. There is a strong coupling between conformational change and cooperative Ca2+ binding at the two C-terminal sites (Maune, 1992b).

Calmodulin (CaM) is an essential component of calcium signaling in multicellular organisms. Null mutations of the Drosophila CaM gene (Cam) were used in combination with clonal analysis and immunolocalization to examine the effects of loss of Cam function in the ovarian germline and developing embryo. These studies have uncovered unexpected and striking movements of CaM protein within these tissues. In the ovary, evidence for transfer of CaM from an external source, across plasma membranes, into the germline cells was obtained. In late embryogenesis, maternally derived CaM protein relocalizes dramatically within the nervous system of both wildtype and Cam null embryos - a process that may also involve movement across cell membranes. These findings indicate dynamic, unsuspected elements to the in vivo functions of CaM in the whole organism (Andruss, 2004).

Calmodulin: Biological Overview | Evolutionary Homologs | Regulation | References

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