Germline/soma distinction in Drosophila embryos requires regulators of zygotic genome activation

Abstract

In Drosophila melanogaster embryos, somatic versus germline identity is the first cell fate decision. Zygotic genome activation (ZGA) orchestrates regionalized gene expression, imparting specific identity on somatic cells. ZGA begins with a minor wave that commences at nuclear cycle (NC)8 under the guidance of chromatin accessibility factors (Zelda, CLAMP, GAF), followed by the major wave during NC14. By contrast, primordial germ cell (PGC) specification requires maternally deposited and posteriorly anchored germline determinants. This is accomplished by a centrosome coordinated release and sequestration of germ plasm during the precocious cellularization of PGCs in NC10. Here, we report a novel requirement for Zelda and CLAMP during the establishment of the germline/soma distinction. When their activity is compromised, PGC determinants are not properly sequestered, and specification is disrupted. Conversely, the spreading of PGC determinants from the posterior pole adversely influences transcription in the neighboring somatic nuclei. These reciprocal aberrations can be correlated with defects in centrosome duplication/separation that are known to induce inappropriate transmission of the germ plasm. Interestingly, consistent with the ability of bone morphogenetic protein (BMP) signaling to influence specification of embryonic PGCs, reduction in the transcript levels of a BMP family ligand, decapentaplegic (dpp), is exacerbated at the posterior pole.

Caspar determines primordial germ cell identity inDrosophila melanogaster

“…Together these two events constitute MZT which is delayed in the germ cell compartment as opposed to soma. Nonetheless, recent data have suggested that the two events possibly occur in a coordinated manner possibly via shared components (C olonnetta et al . 2023).…”

“…2014) suggested that TER94 can potentiate BMP signaling. Interestingly, decapentaplegic ( dpp ), a BMP ligand which is one of the important targets of ZGA regulators including Zelda , can also influence the specification of embryonic PGCs (C olonnetta et al . 2023).…”

The Dynamics of Histone Modifications during Mammalian Zygotic Genome Activation

“…Although the precise timing of these waves and the number of division cycles vary among species [28], the process within a given species is meticulously controlled, exhibiting highly reproducible temporal patterns. Species with rapid development, such as worms [29], frogs [30], fish [31,32], and flies [33,34], complete the MZT and enter gastrulation only hours after fertilization. In contrast, in mammals with a more prolonged development, such as mice [35,36] and humans [37,38], MZT takes one or more days.…”