Role of cellular dynamics, adhesion and polarity in the context of primordial germ cell migration in Xenopus laevis embryos

Abstract

Directional cell migration is an intensively studied process relevant for both normal development of an organism as well as for a number of pathological conditions such as chronic inflammation and cancer. Primordial germ cells (PGCs) in Xenopus laevis embryos can be used as a model system to study cell migration, since during embryogenesis they actively migrate within the endoderm towards genital ridges. Transition to active cell migration is a highly regulated process important for the normal PGC development in many species.This study is focused on molecular and cellular mechanisms involved in initiation of active PGC migration within the endoderm of X. laevis embryos. Analysis of cell shape fluctuations demonstrated that in comparison to pre-migratory neural stage, PGCs isolated from tailbud stage embryos are characterized by an increased cellular dynamics due to formation of bleb-like protrusions and migration via bleb-associated mechanism. Analysis of intracellular PIP3 distribution that depends on the function of kinesin xKIF13B suggests role of PIP3 enrichment in the bleb-like protrusions for PGC polarisation prior to migration, but not for cellular motility during active phase of migration. In addition, cellular adhesion of PGCs to surrounding somatic cells and fibronectin is decreased at the migratory stages, and is not required for the migration in vitro. Whole transcriptome analysis of PGCs and somatic endodermal cells isolated from the neurula and tailbud stages revealed downregulation of several adhesion molecules in migratory PGCs. Downregulated expression of Claudin 6.1, Gap junction protein beta 1 and E-cadherin was confirmed by quantitative RT-PCR analysis with isolated cells.