title: A unique fibrillar coat on the surface of migrating human primordial germ cells.
abstract: Primordial germ cells (PGCs) were studied by electron microscopy in human embryos at 27 and 30 days of gestation. PGCs were mainly found in the hindgut epithelium, some at the stage of separation from the endoderm, and others in migration through the mesenchyme of the dorsal mesentery between the primitive intestinal wall and the coelomic epithelium, including the coelomic angle. A few PGCs were still located in the endodermal epithelium. Before the process of separation and migration, PGCs appeared clearly different from neighboring somatic cells (endodermal, mesenchymal and epithelial cells of the hindgut and the coelomic layer). PGCs located in the endodermal epithelium were large and showed an irregular cell body often provided with filopodia-like processes that contacted somatic cells to form small areas of focal junctions. As a rule, PGCs possessed a large, round nucleus containing one or two conspicuous nucleoli. Lipid droplets, abundant glycogen particles, ribosomes and mitochondria were often observed in their cytoplasm. A detailed ultrastructural analysis revealed a delicate fibrillar coat frequently present on the free surface of PGCs during their migratory phase through the mesenchyme of the dorsal mesentery. This surface coat, likely corresponding to a glycocalyx, appeared as a particular, conspicuous filamentous layer of 30 nm thickness, mainly in the leading pseudopodial projections of PGCs migrating toward their target. The surface coat of PGCs can be associated with the binding sites of specific macromolecular components of the extracellular matrix, including fibronectin, and hence plays a role in PGCs recognition and migration during this special embryonic phase.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Laboratory of Embryology and Electron Microscopy, Faculty of Medicine, University of Chile, Santiago.
authors.forename: J
authors.initials: J
authors.lastname: Pereda
authors.forename: P M
authors.initials: PM
authors.lastname: Motta
mesh_terms: D002462:Cell Membrane / Q000648:ultrastructure; D002465:Cell Movement; D002466:Cell Nucleolus / Q000648:ultrastructure; D002467:Cell Nucleus / Q000648:ultrastructure; D004622:Embryo, Mammalian / Q000166:cytology*; D004707:Endoderm / Q000648:ultrastructure; D004848:Epithelium / Q000648:ultrastructure; D005854:Germ Cells / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure*; D006023:Glycoproteins / Q000032:analysis; D006801:Humans; D008854:Microscopy, Electron; D015388:Organelles / Q000648:ultrastructure; D011134:Polysaccharides / Q000032:analysis; D011554:Pseudopodia / Q000648:ultrastructure
chemical_list: D006023:Glycoproteins; D011134:Polysaccharides