Morphological and cytochemical study of extracellular matrix during the migratory phase of human and mouse primordial germ cells

Primordial germ cells (PGCs), the ancestors of functional gametes in mammal s, originate in an extragonadal location, and then migrate to and colonize the genital ridges during early organogenesis period. PGCs move actively fr om their original site, the wall. of the hindgut, through the extracellular matrix (ECM) of the dorsal mesentery. This movement is controlled in part by components of the ECM. Cells are known to bind to individual ECM glycopr oteins in a complex and poorly understood way. During migration in embryos, PGCs must alter their overall adhesiveness to the endodermal epithelium to allow locomotion. This study examined the ECM: material of the migratory r oute during mouse and human PGCs migration. Mouse embryos obtained from Swi ss Rockefeller mouse and normal human embryos between 4 and 7 weeks of deve lopment, collected during salpingectomy performed on patients with tubal ec topic pregnancies, were analyzed. The study was based on a morphological an alysis using scanning electron microscopy (SEM), and on the histochemical a nd ultracytochemical identification of glycosaminoglycans (GAGs) and proteo glycans. In each age group, the mesenchyme was widely separated by intercel lular spaces and materials. Fine filamentous strands extended between the s urface of mesenchymal cells and the surface of PGCs. Hyaluronan and chondro itin and/or dermatan sulfate were localized in the ECM of the PGC migratory pathway both in mouse and human embryos. Hyaluronan was clearly reduced in the later stage of the migratory processes; on the contrary, the chondroit in sulfate reaction product increased. These results are consistent with pr evious observations showing that hyaluronan is a major component of the ECM , and are also suggestive of the significant role played by hyaluronan, cho ndroitin sulfate and dermatan sulfate during migration, thus providing a pe rmissive substrate for cell migration during development. The observed temp oral and regional patterns suggest that these GAGs are important morphogene tic factors both in the mouse and human although the precise biological fun ction of the proteoglycans are not currently clear.