LOCALIZATION OF RETINOIC ACID RECEPTORS IN ANTERIOR HUMAN EMBRYO

Retinoic acid receptors (RARs) are nuclear transcription factors that are activated by all-trans-retinoic acid or 9-cis-retinoic acid and ar e found in all tissues but predominantly in developing fetus, dividing tumor cells, and adult skin. Three forms of these receptors, alpha, b eta, and gamma, have been described. In this paper we report the prese nce of RAR alpha and beta determined by hybridization with anti-sense messenger RNA, and histochemical localization of the three forms of RA Rs using monospecific polyclonal antibodies in various tissues of earl y human embryos. In a 54-day-old embryo, RAR alpha was expressed prima rily in the liver and the brain, with somewhat lesser expression in th e intestine. RAR beta was the highest in the brain, followed by a rest ricted expression in the intestine and the liver. Other organs, i.e., adrenal, kidney, and testis, did not show measurable amounts of RAR be ta. The immuno-histochemical localization in anterior sections of a 43 -day-old embryo indicated that RAR alpha was present in the neuroepith elial cells and in cells lining the primitive pharyngeal sac, dorsal a orta, and pericardium. RAR beta was somewhat less prevalent in same ti ssues, whereas the expression of RAR gamma was the lowest of the tree RARs in any tissues examined. Results indicated that RAR alpha and bet a appear at early stages of human embryonic development and their expr ession is restricted to certain types of tissues. (C) 1995 Academic Pr ess, Inc.