Oocyte growth in the chicken: receptors and more

The laying hen's left ovary (the ovary on the right side regresses during embryonic development) at any given time contains 5-8 follicles with vitellogenic oocytes, i.e., female germ cells of increasing size ranging from 8 to approx. 30 mm in diameter. Between the 8mm and the 30 mm cell lie about 7 days of massive growth of the oocyte, which in essence occurs via accumulation of yolk. While the chemical composition of the oocyte content, i.e., the yolk, is well known, the origin(s) of this material, its mode(s) of accumulation in the oocyte, and the cell biological details of the oocyte's specialized machineries for maintenance of structural organization and stability have only recently been begun to be elucidated. Here, we outline recent findings in the following areas: (i) the role of low density lipoprotein receptor family members in the transport of yolk precursors from the plasma compartment into oocytes; these findings have implications for metabolic events in certain other tissues such as the brain; and (ii) the synthetic and structural specialization of the granulosa cells, which surround the oocyte within the ovarian follicle, as a model for epithelial cell biology.