Nuclear-fallout, a Drosophila protein that cycles from the cytoplasm to the centrosomes, regulates cortical microfilament organization

Abstract

nuclear fallout (nuf) is a maternal effect mutation that specifically disrupts the cortical syncytial divisions during Drosophila embryogenesis. We show that the nuf gene encodes a highly phosphorylated novel protein of 502 amino acids with C-terminal regions predicted to form coiled-coils. During prophase of the late syncytial divisions, Nuf concentrates at the centrosomes and is generally cytoplasmic throughout the rest of the nuclear cycle. In nuf-derived embryos, the recruitment of actin from caps to furrows during prophase is disrupted. This results in incomplete metaphase furrows specifically in regions distant from the centrosomes. The nuf mutation does not disrupt anillin or peanut recruitment to the metaphase furrows indicating that Nuf is not involved in the signaling of metaphase furrow formation. These results also suggest that anillin and peanut localization are independent of actin localization to the metaphase furrows. nuf also disrupts the initial stages of cellularization and produces disruptions in cellularization furrows similar to those observed in the metaphase furrows. The localization of Nuf to centrosomal regions throughout cellularization suggests that it plays a similar role in the initial formation of both metaphase and cellularization furrows. A model is presented in which Nuf provides a functional link between centrosomes and microfilaments.

Orb-dependent polyadenylation contributes to PLP expression and centrosome scaffold assembly

“…To further examine genome stability, we measured rates of nuclear fallout (NUF), a developmental response to DNA damage in which damaged nuclei are ejected from the syncytial blastoderm cortex and targeted for apoptosis (Sullivan et al, 1993;Rothwell et al, 1998). NUF is readily detected as gaps in the normally uniform monolayer of DAPI-positive nuclei lining the embryonic cortex (dashed lines; Figure 5C).…”

Cytoplasmic divisions without nuclei

“…4B, bottom panel). Importantly, we found that previously reported conditions ( 37–39 ) for eliminating nuclei with spindle segregation errors ( nuclear fallout ; here referred to as “Type 2”) are unlikely to fully account for the elimination of mitotically delayed nuclei from the blastoderm (Fig. S10, Video S5 and Supplementary text S5).…”

“…Nuclear fallout is the spontaneous elimination of nuclei from the blastoderm in fly embryos, observed as a consequence of DNA damages that associated with spindle segregation errors, such as lagging and/or bridging chromosomes ( 37–39 ). Indeed, we also observed that nuclei with these errors were present and, expectedly, were largely eliminated from the blastoderm (Fig.…”

“…(A) Under normal circumstances, nuclei go through mitosis and continue to reside apically in the blastoderm. (B) As demonstrated by a large body of previous studies(37)(38)(39), nuclei with karyotype damages (e.g., lagging chromosomes that form anaphase bridges as indicated by white arrows) are usually eliminated from the blastoderm by fallout (follow white arrow heads). In our experiments, we can observe both nuclear extrusions (Fig.4, A and B; Type 1) and fallouts (depicted here; Type 2) within the same embryos (see Video 4).…”

Bitesize bundles F-actin and influences actin remodeling in syncytialDrosophilaembryo development

“…In addition to actin assembly, membrane trafficking is essential for syncytial blastoderm development. When membrane trafficking is perturbed by knocking down components of the trafficking machinery, such as Nuf and Rab11, pseudo-cleavage furrows are shorter and resemble those in embryos defective in actin assembly (Cao et al, 2008;Holly et al, 2015;Riggs et al, 2003;Rikhy et al, 2015;Rothwell et al, 1998;Sherlekar et al, 2020). Together, these findings indicate that actin network reorganization is coupled with membrane remodeling to create pseudo-cleavage furrows.…”