Retinoids are endogenous to the porcine blastocyst and secreted by trophectoderm cells at functionally-active levels
Published: 1 May 1998
V Parrow, C Horton, M Maden, S Laurie and E Notarianni
Department of Development and Signalling, The Babraham Institute, Cambridge, United Kingdom.
Retinoic acid and its isomers are the major morphogens in vertebrate development. For mammals, it was previously considered that circulating retinoic acid was recruited from the uterine environment, to influence embryonic differentiation, morphogenesis and development. Here we report that retinoic acid is endogenous to the blastocyst of the domestic pig, Sus scrofa, as detected by high pressure liquid chromatography. Furthermore, using a continuous, normal line of porcine trophectoderm cells, TE1, we have identified the trophoblast as a major source of retinoids. Endogenous retinoic acid was found at a concentration of approximately 35 nM in extracts of entire blastocysts, and at a similar concentration in extracts of TE1 cells. Retinoids in explants of blastocysts and in conditioned medium from the TE1 cell line were found to be functionally-active, inducing gene expression from a retinoic-acid-responsive enhancer element in an in vitro assay system. In conclusion, we propose that there is a morphogenetic role for endogenous, and trophoblast-derived, retinoids in the early development of the pre-gastrulation porcine embryo; and that the TE1 cell line therefore provides a useful in vitro system for the study of retinoid metabolism. Furthermore, an implication of this study is that endogenous retinoids may play an active role in the pre-implantation embryology of other species, such as the human.