| [Objetive] To study the effects of Vitamin A deficiency on Retinoic acid receptors development in rats embryonic brain and find out the time window of development to intervene.[Methods] 24 female Wistar rats of 10 weeks were randomly divided into marginal vitamin A-deficient (MVAD) and control groups. They were fed with VA 400IU/kg and 6500IU/kg diets respectively, starting from 3 weeks before copulating. Embryos were collected at 11, 14, 17 and 20 dpc respectively. Body and head (or brain) weights were measured, VA levels in liver and brain were determined by HPLC and RARα, RARβ, RXRβ, Hoxa1, Hoxb1 mRNAs were analysed by RT-PCR.[Results] (1) In MVAD group, embryonic body weights of 17dpc and 20dpc were significantly less than those of the Control group. Compared with the control, the head weights of 20dpc embryos in MVAD group were significantly less, but the brain weights was not so. (2) The VA levels in MVAD embryonic liver and brain were significantly decreased from 17dpc compared with the control. (3) In MVAD embryonic brain, the expression of RARβ mRNA was significantly decreased at 20dpc, and that of RXRβ and Hoxa1 were all decreased from 14dpc compared with the control. In control group, the expression peaks of RARβ, Hoxa1 and Hoxb1 mRNA were all at 14dpc and that of RXRβ was at 20dpc.[Conclusion] (1) MVAD on pregnant rat can block the physique development of embryo. (2) In MVAD group,the expressions of RARβ, RXRβ and Hoxa1 mRNA were decreased before the weight and VA level . Among of them, the change of RXRβ and Hoxa1 were earlier and more sensitive to MVAD than RARβ. (3) One of the mechanisms of Vitamin A on embryonic brain development maybe regulating the expression of Hox genes through retinoic acid receptors. (4) 14dpc maybe a critical window of development in embryonic CNS, so VA supplementation should begin before this time.
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