Ultrastructural characteristics of primordial germ cells and their amoeboid movement to the gonadal ridges in the tammar wallaby.

ABSTRACT

The primordial germ cells (PGCs) of tammar wallaby fetuses are large cells with large nuclei. The cytoplasm of the PGCs contains characteristic spherical mitochondria and abundant ribosomes that make the cyoplasm appear dense. No permanent junctional complexes between PGCs and somatic cells were observed, and there were few cytoplasmic inclusions. The majority of migrating PGCs were observed outside the gonad in the dorsal mesentery and in the tissues adjacent to the gonad. The migrating PGCs have many finger-like, blunt pseudopodia, within which microfilament bundles are observed. The numerous dumbell-like PGCs with polarised cytoplasm suggest that the PGCs of this marsupial move to the gonadal ridges by amoeboid movement, but once the PGCs reach the gonadal ridge, they assume their more characteristic ovoid shape.