THE PATTERN OF RETINOIC ACID RECEPTOR-GAMMA (RAR-GAMMA) EXPRESSION INNORMAL DEVELOPMENT OF XENOPUS-LAEVIS AND AFTER MANIPULATION OF THE MAIN BODY AXIS

Nuclear receptors are a prerequisite for the transduction of retinoid signals in vertebrate embryogenesis. We have raised an antiserum again st the X. laevis retinoic acid receptor gamma (xRARgamma), which speci fically detects a polypeptide with an M(r) of 54 X 10(3) in embryos at gastrula and neurula stages. The antiserum reveals xRARgamma as a nuc lear protein in the head endomesoderm, the neuroectoderm of the hindbr ain region, and the entire posterior region during neurula stages. Exp lanted animal caps express low amounts of xRARgamma in the absence of mesoderm induction. Treatment of animal caps with activin leads to an increase of the amount and to a regionalization of the xRARgamma expre ssion. In exogastrulae and in Keller sandwiches, the pattern of expres sion in the endomesoderm is as expected by analogy to the normal embry o and therefore independent of the vertical contact between the germ l ayers. A planar signal coming from the dorsal mesoderm is sufficient t o impose region-specific expression of xRARgamma in the neuroectoderm of Keller sandwiches.