Onset of meiosis in the chicken embryo; evidence of a role for retinoic acid

Smith, Craig, Roeszler, Kelly, Bowles, Josephine, Koopman, Peter and Sinclair, Andrew (2008) Onset of meiosis in the chicken embryo; evidence of a role for retinoic acid. BMC Developmental Biology, 8 85: . doi:10.1186/1471-213X-8-85

Author Smith, Craig
Roeszler, Kelly
Bowles, Josephine
Koopman, Peter
Sinclair, Andrew
Title Onset of meiosis in the chicken embryo; evidence of a role for retinoic acid
Journal name BMC Developmental Biology   Check publisher's open access policy
ISSN 1471-213X
Publication date 2008-09-17
Year available 2008
Sub-type Article (original research)
DOI 10.1186/1471-213X-8-85
Open Access Status DOI
Volume 8
Issue 85
Total pages 19
Editor Melissa Norton
Place of publication London, United Kingdom
Publisher BioMed Central
Language eng
Formatted abstract
Meiosis in higher vertebrates shows a dramatic sexual dimorphism: germ cells enter meiosis and arrest at prophase I during embryogenesis in females, whereas in males they enter mitotic arrest during embryogenesis and enter meiosis only after birth. Here we report the molecular analysis of meiosis onset in the chicken model and provide evidence for conserved regulation by retinoic acid.

Meiosis in the chicken embryo is initiated late in embryogenesis (day 15.5), relative to gonadal sex differentiation (from day 6). Meiotic germ cells are first detectable only in female gonads from day 15.5, correlating with the expression of the meiosis marker, SCP3. Gonads isolated from day 10.5 female embryos and grown in serum-free medium could still initiate meiosis at day 16.5, suggesting that this process is controlled by an endogenous clock in the germ cells themselves, and/or that germ cells are already committed to meiosis at the time of explantation. Early commitment is supported by the analysis of chicken STRA8, a pre-meiotic marker shown to be essential for meiosis in mouse. Chicken STRA8 is expressed female-specifically from embryonic day 12.5, preceding morphological evidence of meiosis at day 15.5. Previous studies have shown that, in the mouse embryo, female-specific induction of STRA8 and meiosis are triggered by retinoic acid. A comprehensive analysis of genes regulating retinoic acid metabolism in chicken embryos reveals dynamic expression in the gonads. In particular, the retinoic acid-synthesising enzyme, RALDH2, is expressed in the left ovarian cortex at the time of STRA8 up-regulation, prior to meiosis.

This study presents the first molecular analysis of meiosis onset in an avian embryo. Although aspects of avian meiosis differ from that of mammals, a role for retinoic acid may be conserved.
© 2008 Smith et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Keyword Meiosis
Retinoic acid
Avian embryo
Molecular analysis
Q-Index Code C1
Q-Index Status Confirmed Code
Additional Notes This is an online article - Page numbers on pdf version are not for citation purposes.

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