Ovarian dynamics and follicle development in Aves
Maintained by the Johnson laboratory at the University of Notre Dame
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The avian ovary represents a truly dynamic organ system capable of fostering the annual development of one or more broods of viable eggs, then undergoing nearly complete regression followed by eventual recrudescence. A unique morphological and functional aspect of the reproductively active avian ovary, as compared to the mammalian counterpart, is that follicles at all stages of development, from resting primordial and primary follicles to the fully differentiated preovulatory stage, exist simultaneously during egg-laying. As a consequence, the sequential selection of one undifferentiated follicle into the final rapid growth stage of development provides for ovulation of an oocyte from a fully differentiated follicle on an approximate daily basis (the interval between ovulations being species-dependent). The ovarian follicular hierarchy is a reflection of oviparity, and is a feature held in common with avian predecessors, the reptiles and apparently some dinosaurs (Sato et al., Science 308(5720): 375, 2005).
Left ovary of the domestic hen (Gallus gallus) illustrating the hierarchal structure of ovarian follicles. Under environmentally controlled conditions the laying hen will continue to lay eggs on a daily basis for a year or longer with a typical clutch size of 6 to 20+ eggs. F1-5 represent preovulatory follicles 12 to 40 mm in diameter) that have been selected to enter the rapid growth phase of development. SYF, small yellow prehierarchal follicles (6 to 8 mm diameter); SWF, small white prehierarchal follicles (1 to 5 mm). POF, postovulatory follicle. Not readily visible are primordial and primary follicles (<1 mm). Reprinted from Johnson, 1990.
While there are some excellent field studies documenting seasonal changes in reproductive hormones and comparing ovarian dynamics among free ranging species (e.g., see Wingfield and Farner, 1993,The endocrinology of wild species. In: Avian Biology, D.S.Farner, J.R. King, and K.C. Parkes, eds., vol 9, pp. 163-327, Academic Press, New York), the majority of information pertaining to cellular and molecular mechanisms regulating follicle growth and differentiation has been derived primarily from domesticated birds. This is largely due to the quantity and ready availability of tissues required for detailed studies, but nevertheless leaves open the question as to what extent models of ovarian organization and function developed from genetically-manipulated avian models maintained under well-controlled environmental and nutritional conditions directly pertain to wild birds.
This website represents an effort to collate data from previously published plus ongoing genomic, cellular and physiologic studies and make these avian data readily accessible to all comparative reproductive physiologists and endocrinologists for further analyses. It is envisioned that ultimately this resource will highlight the advantages of applying molecular and cellular techniques to address physiological and organismal questions in non-traditional animal model systems. A second objective is to highlight some of the many unresolved questions that can assist both field and bench biologists in developing more refined working models of ovarian function to better understand the remarkably diverse and successful reproductive strategies attributed to avian species.
The following links provide summaries of published and unpublished data related to avian follicle growth, follicle selection, the differentiation of granulosa cells during follicle development, and apoptotic pathways that contribute to avian follicle atresia:
Data generated within the Johnson lab has been funded (1992 to present) by:
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NSF IBN-9419613 NSF IBN-0131185 NSF IOB-0445949 |
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USDA NRICGP 92-37203-8337 USDA NRICGP 95-37203-1998 USDA NRICGP 99-35203-7736 |
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NIH HD36095 |
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DOD DAMD17-03-1-0206 |
