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Origin and Differentiation of the Inner Follicular Cells during Oogenesis in Molgula pacifica (Urochordata), an Ascidian without Test Cells
Author(s) -
Cloney Richard A.
Publication year - 1995
Publication title -
acta zoologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.414
H-Index - 37
eISSN - 1463-6395
pISSN - 0001-7272
DOI - 10.1111/j.1463-6395.1995.tb00985.x
Subject(s) - follicular phase , biology , oocyte , follicular cell , microbiology and biotechnology , epithelium , follicle , compartment (ship) , border cells , ovarian follicle , anatomy , endocrinology , cell , embryo , genetics , oceanography , geology
In Molgula pacifica small previtellogenic oocytes are found between cells of the ovarian epithelium. Each oocyte subsequently grows within a compartment of the epithelium known as a primary follicle. The wall of the primary follicle is composed of outer follicular epithelial cells. While growing from about 15–70 μm in diameter, each oocyte gradually recruits a set of about 950 non‐epithelial inner follicular cells. These cells co‐differentiate in sets with each oocyte, but test cells never appear. The first filamentous components of the vitelline coat appear on the surface of an oocyte in places where it is in contact with undifferentiated (stage 2) inner follicular cells. Each fully differentiated inner follicular cell stores adhesive precursors in a large compartment of the endoplasmic reticulum and probably secretes components of the vitelline coat. There is no evidence that the outer follicular epithelial cells transform into inner follicular cells by dedifferentiation as has often been assumed. Inner follicular cells, in stage 1, are nearly identical to hemoblasts. Hemoblasts may form the inner follicular cells, but to do this they would have to cross the outer follicular epithelium and this phenomenon has not yet been seen.