Survival of Drosophila germline stem cells requires the chromatin binding protein Barrier-to-autointegration factor

Abstract

The nuclear lamina (NL) is an extensive protein network that underlies the inner nuclear envelope. This network includes LAP2emerin-MAN1 domain (LEM-D) proteins that associate with the chromatin and DNA-binding protein Barrier-to-autointegration factor (BAF). Here, we investigate the partnership between three NL Drosophila LEM-D proteins and BAF. In most tissues, only Emerin/ Otefin is required for NL enrichment of BAF, revealing an unexpected dependence on a single LEM-D protein. Prompted by these observations, we studied BAF contributions in the ovary, a tissue where Emerin/Otefin function is essential. We show that germ cellspecific BAF knockdown causes phenotypes that mirror emerin/otefin mutants. Loss of BAF disrupts NL structure, blocks differentiation and promotes germ cell loss, phenotypes that are partially rescued by inactivation of the ATR and Chk2 kinases. These data suggest that, similar to emerin/otefin mutants, BAF depletion activates the NL checkpoint that causes germ cell loss. Taken together, our findings provide evidence for a prominent NL partnership between the LEM-D protein Emerin/Otefin and BAF, revealing that BAF functions with this partner in the maintenance of an adult stem cell population.

Checkpoint activation drives global gene expression changes in Drosophila nuclear lamina mutants

“…To explore the properties of CDGs, we focused on upregulated CDGs (3526 genes) because this gene set is not confounded by changes in gene expression resulting from blocked differentiation, as occurs for downregulated genes. Notably, most (88%,1962/2219) genes upregulated upon baf GLKD correspond to CDGs ( Figure 3C ), consistent with Chk2 activation in baf mutants ( Duan et al 2020b ).…”

“…We completed RNA-seq of RNAs obtained from ovaries of newly born females carrying only the driver transgene ( nosgal4 ) and females carrying both the driver and responder transgenes ( baf GLKD). Extensive GSC loss is observed in newly born baf GLKD ovaries, with a median of 38% of germaria without GSCs ( Figure 1A ) ( Duan et al 2020b ). Comparison between nosgal4 and baf GLKD transcriptomes identified 2219 genes with significantly increased (adj P -value ≤0.05) and 1164 genes with significantly decreased (adj P -value ≤0.05) expression ( Figure 1, B and C and Supplementary Table S1).…”

“…Infertility in emerin mutants is linked to germline stem cell (GSC) loss caused by structural deformation of the NL that non-canonically activates two DNA damage response kinases, Ataxia Telangiectasia and Rad3-related (ATR), and Checkpoint kinase 2 (Chk2; Barton et al 2018 ). G erm- l ine knockdown (GLKD) of BAF also causes GSC loss due to NL deformation and checkpoint kinase activation ( Duan et al 2020b ). Taken together, these findings emphasize the importance of NL integrity for the health and longevity of adult stem cells and tissue homeostasis.…”

Drosophila female germline stem cells undergo mitosis without nuclear breakdown

“…41 Germ-cell-specific BAF depletion also causes NL deformation and GSC loss that is partially rescued by chk2 mutation. 46 These findings indicate that emerin and BAF contribute to shared NL functions needed for GSC maintenance.…”

“…Drosophila GSCs depends upon the integrity of the NL, 37,38 wherein NL deformation is linked to activation of the ATR and Chk2 kinases that leads to GSC loss. 41,46 Here, we investigated mechanisms leading to NL deformation in fGSCs, examining the role of mitosis in shaping the NL. Two main modes of mitosis exist, open and closed.…”