Developmental Northern and Western analyses show coincident accumulation of the 9.5-kb transcript and the 280-kDa protein at all stages of development, with high levels at the embryonic and pupal stages (Mansfield, 1994).
The hyperplastic discs (hyd) gene (formerly called l(3)c43) is located at 85E1-10 on the third chromosome of Drosophila melanogaster. It was originally identified by a temperature-sensitive mutation that causes imaginal disc overgrowth in mutant larvae raised at a restrictive temperature. Twenty new alleles of hyperplastic discs have been recovered in gamma ray, ethyl methanesulfonate and hybrid dysgenesis screens, and the molecular lesions have been identified for several of the alleles. The null phenotype appears to be lethal at or before the second instar. Adults that can be obtained in crosses of temperature-sensitive alleles maintained at permissive temperatures are sterile with one exception and have defects in germ tissue morphology. The hyperplastic discs locus has been cloned by chromosome walking from the alpha-tubulin-2 gene and encodes a 9.5-kb messenger RNA, containing a 2897-amino-acid open reading frame. Sequence analysis of HYD reveals strong similarity to a portion of the C-terminus of poly(A) binding protein and to the rat 100-kDa protein, whose function is unknown. The 280-kDa HYD protein accumulates at decreased levels in mutant alleles and at restrictive temperatures in ts alleles. Examination of relative levels of Hyd protein in mutant animals supports the idea that less severe mutations are those that result in disc overgrowth, while more severe mutations result in variable disc growth phenotypes (Mansfield, 1994).
While hyd clones in third instar eye discs contain Elav-expressing photoreceptors, clones in the adult eye appear to form either scars in the eye or at the margin of the head cuticle. It was also noticed that hyd clones in the posterior of the eye disc are generally smaller than wild-type clones generated in a similar cross, and mutant clones contained reduced numbers of photoreceptors. The lack of mutant ommatidia in adult eyes could reflect either a loss of hyd mutant clones due to competition with the surrounding tissue, or a later requirement of hyd for viability. To further examine this question, hyd clones were made in a Minute genetic background, thereby reversing the growth disadvantage of hyd mutant tissue. These animals survive to pharate adult stages but can not eclose; they have greatly reduced eyes that nevertheless appear to contain properly formed hyd mutant ommatidia. This suggests that the lack of visible hyd clones in adults is due to their poor relative growth, leading to their elimination through competition with wild-type cells. Third instar eye discs containing hyd/Minute clones were also examined, and greatly reduced eye discs were found that appeared to contain full clusters of photoreceptors throughout the eye field. Since cells arrest division when they differentiate, premature differentiation could explain the small size of hyd/Minute eye discs. Ato is normally expressed in the morphogenetic furrow and in the youngest R8 photoreceptors; in early third instar hyd/Minute mutant discs the only remaining Ato staining is in single (presumably R8) cells, implying that the morphogenetic furrow has already reached the anterior margin. From this, it is inferred that differentiation in hyd/Minute discs still progresses from posterior to anterior, but at an accelerated rate (Lee, 2002).
The F-box protein Slmb has been shown to promote processing of Ci to Ci75 as a component of an SCF ubiquitin ligase complex. Therefore the effects were compared of slmb and hyd mutations on Ci levels in the wing disc. Ci155 is much more dramatically increased in slmb clones than in hyd clones. An interesting difference was also observed between hyd and slmb in the regulation of dpp. dpp expression is increased in hyd mutant clones close to the AP border, but is very rarely activated outside this domain. In contrast, slmb mutant clones activated dpp expression only when they lay outside the wing pouch, perhaps because of activation of Wg signaling, which represses dpp expression, within the wing pouch. Consistent with these third instar phenotypes, anterior duplications like those resulting from loss of slmb are not observed in adult wings containing hyd mutant clones, although outgrowths did arise from internal regions of the wing. Such duplications would require dpp to be misexpressed at a distance from its normal domain of expression. Ptc expression, which requires activation of the full-length form of Ci, was not altered in either hyd or slmb mutant clones. Slmb and Hyd thus appear to have distinct effects on Ci protein accumulation and activity, suggesting that they have either different substrates or different effects on the same substrate (Lee, 2002).
Callaghan, M. J., Russell, A. J., Woollatt, E., Sutherland, G. R., Sutherland, R. L. and Watts, C. K. (1998). Identification of a human HECT family protein with homology to the Drosophila tumor suppressor gene hyperplastic discs. Oncogene 17: 3479-3491. 10030672
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Deo, R. C., Sonenberg, N. and Burley, S. K. (2001). X-ray structure of the human hyperplastic discs protein: an ortholog of the C-terminal domain of poly(A)-binding protein. Proc. Natl. Acad. Sci. USA 98: 4414-4419. 11287654
Henderson, M. J., et al. (2002). EDD, the human hyperplastic discs protein, has a role in progesterone receptor coactivation and potential involvement in DNA damage response. J. Biol. Chem. 277(29): 26468-78. 12011095
Honda, Y., Tojo, M., Matsuzaki, K., Anan, T., Matsumoto, M., Ando, M., Saya, H. and Nakao, M. (2002). Cooperation of HECT-domain ubiquitin ligase hHYD and DNA topoisomerase II-binding protein for DNA damage response. J. Biol. Chem. 277: 3599-3605. 11714696
Kozlov, G., Trempe, J. F., Khaleghpour, K., Kahvejian, A., Ekiel, I. and Gehring, K. (2001). Structure and function of the C-terminal PABC domain of human poly(A)-binding protein. Proc. Natl. Acad. Sci. 98: 4409-4413
Lee, J. D., Amanai, K., Shearn, A. and Treisman, J. E. (2002). The ubiquitin ligase Hyperplastic discs negatively regulates hedgehog and decapentaplegic expression by independent mechanisms. Development 129: 5697-5706. 12421709
Mansfield, E., Hersperger, E., Biggs, J. and Shearn, A. (1994). Genetic and molecular analysis of hyperplastic discs, a gene whose product is required for regulation of cell proliferation in Drosophila melanogaster imaginal discs and germ cells. Dev. Biol. 165: 507-526. 7958417
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Oughtred, R., et al. (2002). Characterization of rat100, a 300-kilodalton ubiquitin-protein ligase induced in germ cells of the rat testis and similar to the Drosophila hyperplastic discs gene. Endocrinology 143(10): 3740-7. 12239083
date revised: 22 November 2002
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