Retinoid receptor-specific agonists regulate bovine in vitro early embryonic development, differentiation and expression of genes related to cell cycle arrest and apoptosis.

ABSTRACT

A major goal in reproductive biotechnology is the identification of pathways that regulate early embryonic development and the allocation of cells to the inner cell mass (ICM) and trophectoderm (TE). Retinoids regulate the development and differentiation of the bovine blastocyst in vitro, although the involvement of the retinoid X receptors (RXRs) remains to be clarified. This paper compares the effect of a synthetic RXR agonist (LG100268; LG) with that of the retinoic acid receptor (RAR) agonist all-trans retinoic acid (ATRA) on blastulation. In vitro-produced morulae were treated for 48 h with LG (0.1 microM, 1 microM and 10 microM), ATRA 0.7 microM, or no additives. Treatment with ATRA did not increase the rate of development; however, the LG 0.1 microM treatment increased both the blastocyst development and hatching rate. Cell numbers increased in the ICM with LG 10 microM, while a dose-dependent reduction was observed in the TE in the presence of LG. Gene expression levels of p53 and p66 did not vary with LG but increased with ATRA. Both LG and ATRA activated bax, a pro-apoptotic gene and H2A.Z, a cell cycle-related gene. The above effects suggest the existence of active p53-dependent and -independent apoptotic pathways for ATRA and LG, respectively, in the bovine embryo. The expression of p53 and H2A.Z showed a strong, positive correlation (r=0.93; p<0.0001) in all experimental groups; both proteins are linked through the cell cycle. Agonists of RXR could be used to control blastocyst development and differentiation.