Anteroposterior patterning and organogenesis of Xenopus laevis require a correct dose of germ cell nuclear factor (xGCNF)

The germ cell nuclear factor of Xenopus laevis (xGCNF; NR6A1) is a nuclear orphan receptor that is predominantly expressed during neurula and late tai lbud stages. As a strategy to analyze the role of xGCNF in embryogenesis, w e have induced a gain of function by overexpression of full-length (fl) GCN F and a functional inhibition by a dominant-negative (dn) GCNF. Early event s of embryogenesis including grastrulation and neurulation were not affecte d and the expression of several early mesodermal markers was normal. Yet sp ecific defects were observed upon organogenesis. Ectopic posterior overexpr ession of the full-length xGCNF caused posterior defects and disturbed somi te formation. In contrast, expression of dnGCNF interfered with differentia tion of the neural tube and affected the differentiation of anterior struct ures, including the cement gland and the eyes. Embryos affected by dnGCNF w ere rescued by coexpression of flGCNF. After expression of dnGCNF, mRNA enc oding the retinoic acid receptor xRAR(gamma 2) was selectively suppressed a nteriorly. From the distinct phenotypes obtained, we conclude that GCNF has an essential function in anteroposterior differentiation during organogene sis. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.