Fine structural observations on the origin and associations of primordial germ cells of the mouse

Abstract

This study explores the origin of primordial germ cells (PGCs) of the mouse and examines their morphology and associations with other cells during early development. PGCs have been selectively stained by the alkaline phosphatase histochemical reaction and viewed by light and electron microscopy from the time they are first detectable in the yolk sac endoderm until they enter the gonadal ridges. There are conflicting reports as to whether the PGCs originate from endodermal cells or whether they originate elsewhere and subsequently enter the endoderm. The observations in the present study favor the premise that PGCs of the mouse do not originate in the endoderm. Furthermore, it was observed that PGCs undergo specific changes in morphology during the developmental period studied and this was interpreted to mean that, although PGCs are set aside early in development as a distinct cell line, they also continue to become more specialized within time. The germ cell line is rather unusual in that it does not exist as a discrete tissue but, instead, resides within various other tissues during its life history. This apparent dependence upon somatic cells is maintained even in adult animals and may be important in serving to maintain or modify the environment of the germ cells.