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Formation of Ovarian Follicles During Fetal Development in Sheep
The origin of follicle (i.e., pregranulosa) cells that become the somatic component of primordial follicles is obscure. In addition, information regarding the structural changes that accompany the concomitant regression of ovigerous cords and the appearance of primordial follicles is lacking. In the...
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Published in: | Biology of reproduction 2002-04, Vol.66 (4), p.1134-1150 |
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Main Authors: | , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that cite this one |
Online Access: | Get full text |
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Summary: | The origin of follicle (i.e., pregranulosa) cells that become the somatic component of primordial follicles is obscure. In
addition, information regarding the structural changes that accompany the concomitant regression of ovigerous cords and the
appearance of primordial follicles is lacking. In the present study, ovine ovaries collected at frequent time intervals between
Day 38 and Day 100 of fetal life were examined by light and electron microscopy. To gain new information regarding the origin
of follicular cells, incorporation of 5-bromo-2â²-deoxyuridine was used to identify proliferating cells at selected stages
of development. Based on the location and identity of proliferating cells, apoptotic cells, and sequential changes in histoarchitecture,
we hypothesize 1) that most (i.e., >95%) of the granulosal cells in newly formed primordial follicles originate from the ovarian
surface epithelium; 2) that the sequential events leading to follicle formation take place entirely within ovigerous cords,
with the first follicles forming at the interface of the cortex and medulla; and 3) that the loss (i.e., >75%) of germ cells,
but not of somatic cells, within the ovigerous cords is a means by which each surviving oocyte gains additional pregranulosal
cells before follicle formation. Conceptual models detailing the chronology of developmental events involved in the formation
of primordial follicles in sheep are discussed. |
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ISSN: | 0006-3363 1529-7268 |
DOI: | 10.1095/biolreprod66.4.1134 |