Mutations in the insulator protein Suppressor of Hairy wing induce genome instability

Abstract

Chromatin insulator proteins mediate the formation of contacts between distant insulator sites along chromatin fibers. Long-range contacts facilitate communication between regulatory sequences and gene promoters throughout the genome, allowing accurate gene transcription regulation during embryo development and cell differentiation. Lack of insulator function has detrimental effects often resulting in lethality. The Drosophila insulator protein Suppressor of Hairy wing [Su(Hw)] is not essential for viability, but plays a crucial role in female oogenesis.The mechanism(s) by which Su(Hw) promotes proper oogenesis remains unclear. To gain insight into the functional properties of chromatin insulators, we further characterize the oogenesis phenotypes of su(Hw) mutant females. We find that mutant egg chambers frequently display an irregular number of nurse cells, have poorly formed microtubule organization centers (MTOC) in the germarium, and show mislocalized Gurken (Grk) in later stages of oogenesis. Furthermore, eggshells produced by partially rescued su(Hw) mutant females exhibit dorsoventral patterning defects that are identical to defects found in spindle mutants or in piRNA pathway mutants.Further analysis reveals an excess of DNA damage in egg chambers, which is independent of activation of transposable elements, and that Gurken localization defects and oogenesis progression are partially rescued by mutations in mei-41 and chk1 genes. In addition, we show that Su(Hw) is required for chromosome integrity in dividing neuroblasts from larval brains.Together, these findings suggest that Su(Hw) plays a critical role in maintaining genome integrity during germline development in Drosophila females as well as in dividing somatic cells.

A Phosphorylated Histone H2A Variant Displays Properties of Chromatin Insulator Proteins inDrosophila

“…Beyond its canonical insulator functions, the Drosophila insulator protein Su(Hw) has been implicated in transcriptional regulation and is required for development of testes and ovaries (Soshnev et al , 2013, Duan and Geyer, 2018). Mutation of su(Hw) interferes with normal DNA damage repair (Lankenau et al, 2000) and lack of Su(Hw) protein results in chromosomal aberrations in developing neuroblasts (Hsu et al, 2020). While these results point to a role in maintaining genome stability, the mechanistic link between Su(Hw) and DNA repair remains uncharacterized.…”

“…Of the gypsy insulator proteins, Su(Hw) is perhaps the best-characterized. Mutation of su(Hw) is associated with female infertility (Klug et al, 1968, Harrison et al, 1993, Baxley et al, 2011, Hsu et al, 2020) and alters the cell’s response to DNA damage (Lankenau et al, 2000). Outside of the gypsy insulator complex, Su(Hw) binds many sites alone or in conjunction with either Mod(mdg4)67.2 or CP190 (Adryan et al, 2007, Kuhn-Parnell et al, 2008, Bushey et al, 2009, Negre et al, 2010, Soshnev et al, 2012, Baxley et al, 2017).…”

“…Mutation of su(Hw) leads to defects in the formation of ring canals between nurse cells, preventing the proper transport of maternal morphogens during ovary development (Hsu et al, 2015). Ovaries in su(Hw) mutants also exhibit malformed microtubule organizing centers and mislocalization of Gurken, a morphogen normally sequestered to one end of the oocyte to direct axis determination in embryos (Hsu et al, 2020). Similar to its role in oogenesis, Su(Hw) is critical for spermatogenesis through its activity as a transcriptional repressor in somatic cyst cells in the male germline (Duan and Geyer, 2018).…”

“…Like H2AX, H2Av is phosphorylated in response to DNA damage (Madigan et al, 2002), and like H2AZ, phosphorylation of H2Av is involved in transcriptional regulation through activation of poly(ADP-ribose) polymerase 1 (PARP1) (Kotova et al, 2011). Our laboratory previously demonstrated an accumulation of phosphorylated H2Av (γH2Av) signal in the ovaries of su(Hw) mutants and the presence of chromosomal aberrations in actively dividing larval neuroblasts lacking Su(Hw), suggesting a significant connection between Su(Hw) activity and genome stability (Hsu et al, 2020). Furthermore, disruption of Mei-41/ATR, a kinase responsible for phosphorylating H2Av among other targets upon DNA damage (LaRocque et al, 2007), partially rescues the defective oogenesis phenotype associated with mutation of su(Hw) (Hsu et al, 2020).…”

“…Our laboratory previously demonstrated an accumulation of phosphorylated H2Av (γH2Av) signal in the ovaries of su(Hw) mutants and the presence of chromosomal aberrations in actively dividing larval neuroblasts lacking Su(Hw), suggesting a significant connection between Su(Hw) activity and genome stability (Hsu et al, 2020). Furthermore, disruption of Mei-41/ATR, a kinase responsible for phosphorylating H2Av among other targets upon DNA damage (LaRocque et al, 2007), partially rescues the defective oogenesis phenotype associated with mutation of su(Hw) (Hsu et al, 2020). While insulator-binding proteins have been described for their role in genome organization and regulation in Drosophila , the mechanisms linking their activity to DNA repair remain elusive.…”