The FoxO-subclass in Xenopus laevis development

Abstract

Transcription factors of the Fox ( fork head b ox) family are involved in cellular specification and determination processes. Here, we report on the isolation and first characterisation of two members of the FoxO subclass in Xenopus laevis, xFoxO1 and xFoxO3. These sequences exhibit 68% (67%) and 69% (70%) identity to their mouse (human) orthologues, respectively. Serine and threonine residues, which are phosphorylated upon insulin signalling, are evolutionarily conserved from frogs to mammals. xFoxO1 and xFoxO3 genes are maternally transcribed, but transcripts disappear during early cleavage stages. Zygotic transcription of both genes starts at the late neurula stages and transcripts accumulate at the end of organogenesis. While maternal transcripts of both genes are found within the animal half of the early embryo, zygotic transcripts show distinct patterns. xFoxO1 expression is observed in the pronephros, within head mesenchyme in front of the eye, within the branchial arches and in the liver primordium. At the late neurula, xFoxO3 is found to be specifically expressed in the anterior neural plate and in neural crest cells. Later, expression of xFoxO3 is observed in a variety of organs and tissues, like the head, the branchial arches and the somites.