Abstract
Two distinct mechanisms for primordial germ cell (PGC) specification are observed within Bilatera: early determination by maternal factors or late induction by zygotic cues. Here we investigate the molecular basis for PGC specification in Nematostella, a representative pre-bilaterian animal where PGCs arise as paired endomesodermal cell clusters during early development. We first present evidence that the putative PGCs delaminate from the endomesoderm upon feeding, migrate into the gonad primordia, and mature into germ cells. We then show that the PGC clusters arise at the interface between hedgehog1 and patched domains in the developing mesenteries and use gene knockdown, knockout and inhibitor experiments to demonstrate that Hh signaling is required for both PGC specification and general endomesodermal patterning. These results provide evidence that the Nematostella germline is specified by inductive signals rather than maternal factors, and support the existence of zygotically-induced PGCs in the eumetazoan common ancestor.
Highlights
Animal embryos typically set aside a group of primordial germ cells (PGCs) that later mature into germline stem cells (GSCs) and in turn give rise to gametes during adulthood (Nieuwkoop and Sutasurya, 1979, 1981; Wylie, 1999; Juliano, Swartz and Wessel, 2010)
Further supporting their germline identity, we found that tudor was enriched in putative PGC clusters (Fig. S1 M-P)
We confirm that Nematostella putative PGCs form in pharyngeal endomesoderm and provide evidence that these cells delaminate via epithelial-mesenchymal transition (EMT) and migrate through the mesoglea to populate the eight gonad primordia
Summary
Animal embryos typically set aside a group of primordial germ cells (PGCs) that later mature into germline stem cells (GSCs) and in turn give rise to gametes during adulthood (Nieuwkoop and Sutasurya, 1979, 1981; Wylie, 1999; Juliano, Swartz and Wessel, 2010). Comparative studies on germ cell development have defined two common mechanisms of PGC specification among diverse animals: preformation and epigenesis During PGC specification by preformation (e.g. Drosophila, C. elegans and Danio rerio), cytoplasmic determinants referred to as the germ plasm are maternally deposited into embryos and segregated into specific blastomeres through cell division (Strome and Wood, 1982; Williamson and Lehmann, 1996; Yoon, Kawakami and Hopkins, 1997). The epigenesis mode of PGC specification is more prevalent across the animal kingdom, and hypothesized to reflect mechanisms present in the cnidarian-bilaterian common ancestor (Extavour and Akam, 2003). To date, no mechanistic studies of PGC specification in early branching animals have functionally tested this hypothesis
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
