{-}{-}{-}Pleiotropic Functions of the Chromodomain-Containing Protein Hat-trick During Oogenesis in Drosophila melanogaster

Chromatin-remodeling proteins play a profound role in the transcriptional regulation of gene expression during development. Here, we have shown that the chromodomain-containing protein Hat-trick is predominantly expressed within ­­­­the oocyte nucleus, specifically within the heterochromatinized karyosome and that a mild expression is observed in follicle cells. Co-localization of Hat-trick with Heterochromatin Protein 1 and a Synaptonemal Complex component- C(3)G along with the diffused karyosome after hat-trick down-regulation shows the role of this protein in heterochromatin clustering and karyosome maintenance. Germline mosaic analysis reveals that hat-trick is required for maintaining the dorso-ventral patterning of eggs by regulating the expression of Gurken. The increased incidence of Double strand breaks (DSBs), delayed DSB repair, defects in karyosome formation, altered Vasa mobility and consequently misexpression and altered localization of Gurken in hat-trick mutant egg chambers, clearly suggest a putative involvement of Hat-trick in the early stages of oogenesis. In addition, based on phenotypic observations in hat-trick mutant egg chambers, we speculate a substantial role of hat-trick in cystoblast proliferation, oocyte determination, nurse cell endoreplication, germ cell positioning, cyst encapsulation, and nurse cell migration. Our results demonstrate that hat-trick has profound pleiotropic functions during oogenesis in Drosophila melanogaster.

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