Zebrafishdazlregulates cystogenesis upstream of the meiotic transition and germline stem cell specification and independent of meiotic checkpoints

Abstract

StatementWe show that zebrafish dazl is required for incomplete cytokinesis to generate germline cysts during cystogenesis, acts upstream of germline stem cell establishment, and is required for meiosis, and fertility. AbstractFertility and gamete reserves are maintained by asymmetric divisions of the germline stem cells to produce new stem cells or daughters that differentiate as gametes. Before entering meiosis, differentiating germ cells (GCs) of sexual animals typically undergo cystogenesis. This evolutionary conserved process involves synchronous and incomplete mitotic divisions of a germ cell daughter (cystoblast) to generate sister cells connected by stable intercellular bridges that facilitate exchange of materials to support a large synchronous population of gamete progenitors. Here we investigate cystogenesis in zebrafish and identified Deleted in azoospermia (Dazl), a conserved vertebrate RNA binding protein as a regulator of this process. Analysis of dazl mutants revealed an essential role for Dazl in regulating incomplete cytokinesis and germline cyst formation before the meiotic transition. Accordingly, dazl mutant GCs form defective ring canals, and ultimately remain as individual cells that fail to differentiate as meiocytes. In addition

Direct male development in chromosomally ZZ zebrafish

“…Germ cell marker genes, including dazl, ddx4, and dnd1 (Olsen et al, 1997;Yoon et al, 1997;Maegawa et al, 1999;Howley and Ho, 2000;Ciruna et al, 2002;Tan et al, 2002;Weidinger et al, 2003;Krovel and Olsen, 2004;Slanchev et al, 2005;Houwing et al, 2008;Saito et al, 2011;Hartung et al, 2014;Hong et al, 2016;Bertho et al, 2021) were detected in the merged 19dpf+30dpf ("1930") data as J). Cluster 1930c16 contained 19dpf cells mixed with 30dpf cells, but the large group of dnd1-expressing clusters contained almost exclusively 30dpf ZW cells (Figure 4B).…”

“…Cell-type marker genes help characterize cluster identities (Qiu et al, 2021) (Supplementary Table S4). Germ cells are marked by a number of genes encoding RNA-binding proteins, including dazl, adad1, ddx4, and dnd1 as well as novel markers including si:ch73-167f10.1 (Fu et al, 2015;Bertho et al, 2021). Expression of these Frontiers in Cell and Developmental Biology frontiersin.org Frontiers in Cell and Developmental Biology frontiersin.org genes identified the 19dpf cluster 17 (19c17) as germ cells (Figures 3C, D, Supplementary Table S4).…”