title: Primordial germ cells and oocytes of Branchiostoma virginiae (Cephalochordata, Acrania) are flagellated epithelial cells: relationship between epithelial and primary egg polarity.
abstract: Primordial germ cells (PGCs) are described from the gonad of c. 2 cm juvenile Branchiostoma virginiae; early oocytes (c. 10 microm) and enlarging, previtellogenic oocytes (c. 35 microm) are described from the ovary of c. 5 cm adults. The germinal epithelium of the juvenile gonad and adult ovary is composed of both germinal and somatic cells. In the juvenile, somatic cells retain contact with the basal lamina of the germinal epithelium though their perikarya may be displaced towards the lumen; the germinal epithelium is, therefore, a simple but pseudostratified epithelium. In the adult ovary, somatic cells may lose contact with the basal lamina and the epithelium appears to become stratified. PGCs and oocytes are identified as germ cells by the presence of nuage. PGCs and oocytes are polarised epithelial cells. They rest on a basal lamina, extend apically towards a lumen, form adhering junctions with neighbouring cells, and exhibit apical-basal polarity. PGCs and early oocytes have an apical flagellum with an associated basal body, accessory centriole, and one or more striated rootlet fibres. The flagellum is surrounded by a collar of microvilli. Once oocytes begin to enlarge and bulge basally into the connective tissue layer, the flagellum is lost, but the basal bodies and ciliary rootlets are present at the apex of 35 microm oocytes. Similarities of the oogenic pattern in cephalochordates and echinoderms indicate that the establishment of egg polarity in deuterostomes is influenced by the polarity of the germinal epithelium.
authors.affiliation: Department of Biological Sciences, Clemson University, South Carolina 29634-1903, USA. jefrick@clemson.edu
authors.forename: J E
authors.initials: JE
authors.lastname: Frick
authors.forename: E E
authors.initials: EE
authors.lastname: Ruppert
mesh_terms: D000818:Animals; D016764:Cell Polarity; D002816:Chordata, Nonvertebrate / Q000166:cytology* / Q000196:embryology*; D004847:Epithelial Cells; D004848:Epithelium / Q000502:physiology / Q000648:ultrastructure; D005260:Female; D005407:Flagella / Q000648:ultrastructure; D005854:Germ Cells / Q000166:cytology* / Q000502:physiology / Q000648:ultrastructure; D006066:Gonads / Q000196:embryology / Q000648:ultrastructure; D009865:Oocytes / Q000166:cytology* / Q000502:physiology / Q000648:ultrastructure; D010053:Ovary / Q000196:embryology / Q000648:ultrastructure; D010063:Ovum / Q000166:cytology* / Q000502:physiology / Q000648:ultrastructure