Development without germ cells: The role of the germ line in zebrafish sex differentiation

TLDR

Primordial germ cells are specified early, migrate to the gonad, and differentiate into sperm or eggs. The study investigates how germ cells influence somatic development and sex differentiation in zebrafish. Germ cells were ablated by dead‑end knockdown and by a parD toxin–antitoxin system that expressed the toxin Kid in PGCs while protecting somatic cells with the antidote Kis. Fish lacking primordial germ cells developed exclusively as males, revealing that the germ line promotes female development.

Abstract

The progenitors of the gametes, the primordial germ cells (PGCs) are typically specified early in the development in positions, which are distinct from the gonad. These cells then migrate toward the gonad where they differentiate into sperms and eggs. Here, we study the role of the germ cells in somatic development and particularly the role of the germ line in the sex differentiation in zebrafish. To this end, we ablated the germ cells using two independent methods and followed the development of the experimental fish. First, PGCs were ablated by knocking down the function of dead end , a gene important for the survival of this lineage. Second, a method to eliminate the PGCs using the toxin–antitoxin components of the parD bacterial genetic system was used. Specifically, we expressed a bacterial toxin Kid preferentially in the PGCs and at the same time protected somatic cells by uniformly expressing the specific antidote Kis. Our results demonstrate an unexpected role for the germ line in promoting female development because PGC-ablated fish invariably developed as males.