Adhesion molecules for mouse primordial germ cells

In the present article we will focus on the adhesion molecules expressed by mouse primordial germ cells (PGCs) and will discuss the role that they play, or are believed to play, in two crucial processes of PGC development, namely cell lineage specification and migration into the gonadal ridges. Recent findings indicate that the adhesion-dependent allocation of the PGC precursors to a niche within the epiblast and the forming extraembryonic mesoderm during the pre-gastrulation period is crucial for their commitment. Subsequently, PGC migration and homing within the gonadal ridges require integrated signals involving contact of PGCs with extracellular matrix molecules and cellular substrates or repulsion from them, adhesion among PGCs themselves and attraction by the developing gonads. A number of adhesion, or putative adhesion molecules, have been identified in mammalian PGCs, mainly in the mouse. These molecules belong to three adhesion molecule families such as cadherins (E-P- and N-cadherins), integrins and the IgG superfamily (PECAM-1). Moreover oligosaccarides (LewisX) and growth factor receptors (c-Kit) can also play adhesive roles in some stages of PGC development. An understanding of how genes encoding adhesive molecules are regulated in PGCs and the molecular pathways associated with the functions of adhesion receptors is crucial in furthering our knowledge of PGC biology. Adhesion molecules might once again turn out to be crucial in controlling not only the germ cell lineage and PGC migration but also the PGC differentiation fate itself.