Distribution and space-time relationship of proteoglycans in the extracellular matrix of the migratory pathway of primordial germ cells in mouse embryos

In this paper we present an in situ ultrastructural cytochemical study on t he distribution and spatial-temporal expression of proteoglycans (PGs) in t he extracellular matrix of the migratory pathway of mouse primordial germ c ells (PGCs) during the different phases of migration, by the use of the cat ionic dye ruthenium hexammine trichloride (RHT). Embryos of 9, 10, 11 and 1 2 days of development were used, The treatment with RHT revealed PGs as ele ctron dense layers, granules, and filaments. Whereas granules prevailed in the extracellular spaces of the migratory route during the whole migratory process, the amount of filamentous structures increased during the migratio n phase of PGCs. At the end of the migratory process the surface of the PGC s lost its reaction by RHT, There were differences in the size of the granu les of PGs at the initial migratory period (9-day-old embryos) as compared with the other days of gestation. There was a strong reaction for PGs in th e extracellular spaces, expressed as a meshwork of granules interconnected by filaments, as well as reaction on the basement membranes during the peak of the PGCs migration in 10-day-old embryos. These results support the hyp othesis that these molecules may have an important role in the migration of PGCs, although the precise mechanism involved in this process is not yet c lear.