MASTL is essential for anaphase entry of proliferating primordial germ cells and establishment of female germ cells in mice

Sanjiv Risal,Jingjing Zhang,Mengwen Hu,Zijiang Chen,Jingchen Shao,Kiran Busayavalasa,Zhaowei Tu,Philipp Kaldis,Kui Liu,Xiaoman Liu,Deepak Adhikari

doi:10.1038/celldisc.2016.52

Abstract

In mammals, primordial germ cells (PGCs) are the embryonic cell population that serve as germ cell precursors in both females and males. During mouse embryonic development, the majority of PGCs are arrested at the G2 phase when they migrate into the hindgut at 7.75–8.75 dpc (days post coitum). It is after 9.5 dpc that the PGCs undergo proliferation with a doubling time of 12.6 h. The molecular mechanisms underlying PGC proliferation are however not well studied. In this work. Here we studied how MASTL (microtubule-associated serine/threonine kinase-like)/Greatwall kinase regulates the rapid proliferation of PGCs. We generated a mouse model where we specifically deleted Mastl in PGCs and found a significant loss of PGCs before the onset of meiosis in female PGCs. We further revealed that the deletion of Mastl in PGCs did not prevent mitotic entry, but led to a failure of the cells to proceed beyond metaphase-like stage, indicating that MASTL-mediated molecular events are indispensable for anaphase entry in PGCs. These mitotic defects further led to the death of Mastl-null PGCs by 12.5 dpc. Moreover, the defect in mitotic progression observed in the Mastl-null PGCs was rescued by simultaneous deletion of Ppp2r1a (α subunit of PP2A). Thus, our results demonstrate that MASTL, PP2A, and therefore regulated phosphatase activity have a fundamental role in establishing female germ cell population in gonads by controlling PGC proliferation during embryogenesis.

Highlights

Primordial germ cells (PGCs) are embryonic cells that serve as progenitors of female and male gametes, and eventually differentiate into oocyte and sperm [1, 2]
The mammalian cell cycle is driven by sequential activation of different types of cyclin-dependent kinases (CDKs) [13, 14], and genetic studies in mice have shown that Cdk1 is the most important Cdk for entry and progression through mitosis [15, 16]
Phosphorylated ENSA/ARPP19 can bind to PP2A-B55 (PP2A with its regulatory subunit B55) and inhibit PP2A activity, which occurs at the same time when Cdk1 activity peaks [23,24,25,26]

Summary

Introduction

Primordial germ cells (PGCs) are embryonic cells that serve as progenitors of female and male gametes, and eventually differentiate into oocyte and sperm [1, 2]. Studies in human cell lines, mouse embryonic fibroblasts (MEFs), and D. melanogaster demonstrated that the activation of the Greatwall kinase (GWL) or its mammalian orthologue MASTL (microtubule-associated serine/ threonine kinase-like) is essential for G2-M phase transition and mitotic progression [20,21,22]. Phosphorylated ENSA/ARPP19 can bind to PP2A-B55 (PP2A with its regulatory subunit B55) and inhibit PP2A activity, which occurs at the same time when Cdk activity peaks [23,24,25,26]. These regulatory events ensure the maximal phosphorylation of Cdk substrates to complete mitosis as shown in Xenopus egg extracts [24]

Methods

Results

Conclusion