Integrin signalling in pluripotent cells acts as a gatekeeper of mouse germline entry

Primordial germ cells (PGCs) are the undifferentiated precursors of gametes and the sole mechanism by which genetic information is transmitted across generations through the germline. They appear at the proximal posterior region of the mouse embryo, where the somatic germ layers begin to emerge and a series of dramatic morphological changes occur at the onset of gastrulation. While the transcriptional and epigenetic mechanisms that drive entry into the germline have been extensively characterised, whether there is a morphogenetic control of the germline-soma bifurcation has never been explored. Here, we uncover a novel and critical role for integrin signalling in regulating germline entry. *In vivo*, we show that mouse PGCs have diminished integrin signalling interactions with the underlying basement membrane and specify in a region that is physically segregated from it. In line with this, the addition of an exogenous extracellular matrix (ECM) inhibits PGC specification in *in vitro*-cultured mouse embryos, as well as during PGC-like cell (PGCLC) specification in both mouse and human *in vitro* stem cell models. Mechanistically, we demonstrate that β1 integrin signalling, in response to the ECM protein, laminin, blocks mouse PGCLC specification by inhibiting Wnt signalling, which leads to failed downregulation of the PGC transcriptional repressor, Otx2, during a critical window of competence. Therefore, integrin signalling restricts mouse germline entry, pointing to a mechanism through which the loss of basement membrane contact by epiblast cells *in vivo* acts as a morphogenetic fate switch during the germline-soma bifurcation.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2023

Author dc:creator

• Makhlouf, Aly

Advisor dc:contributor.advisor

• Shahbazi, Marta

• developmental biology
• embryology
• germline
• stem cells

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/5f77e1f1-051c-40ae-9880-826ada365d2f/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

Author Identifier

0000-0003-4025-0576

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/368237