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A fork head related multigene family is transcribed in Xenopus laevis embryos.
We have isolated and sequenced ten different members of the fork head/HNF-3 multigene family from Xenopus laevis which have been termed Xenopus fork head domain related (XFD) genes 1 to 10. Another four isolated genes (XFD'' genes) represent pseudo-allelic variants which arose by an ancient tetraploidization within this species. Whereas all genes of this multigene family exhibit a high degree of sequence homology within the evolutionary conserved fork head domain, sequences outside this module are substantially different. Based upon sequence homologies over the entire coding sequences, XFD-7/7'' represent the Xenopus homologs to the rodent hepatocyte nuclear factor HNF-3 alpha, while XFD-3/3'' encode the homologs to HNF-3 beta. Here we present an analysis of the temporal transcription pattern of XFD genes 1 to 10 during embryogenesis and in some adult tissues. Eight of these XFD genes are activated during embryonic development, but show different and distinct transcription profiles. The localization of transcripts was determined by whole-mount in situ hybridization. Although transcription of individual XFD genes partially overlaps, each gene is characterized by means of a specific spatial pattern of transcriptional activity.
Fig. 5. localization of XFD gene transcripts in Xenopus embryos by whole-mount in situ hybridization. XFD-1: embryos at gastrula (stage 11) [A,B] and transverse section through an embryo at early neurula (srage 13) [C]. XFD-2: blastula (stage 8) embryo [D], section through the animal cap [E] and late gastrula (stage 12) embryo [F]. XFD-3: transverse section through an embryo (stage 23) at the anterior hindbrain region [G]. stage 23 [H] and tai1bud (stage 28) (I) embryos. XFD-4: embryos at stage 16 [J]. stage 32 [K] and stage 37 [L]. Arrows [J] denote pre-somitogenic mesoderm, arrowhead [K] points towards intense staining at the tip of the tail. XFD-6: embryos at stage 17 [M]. stage 19 [N] and stage 23 [O]. Arrows and arrow. heads denote two types of cell populations differentiating to cranial neural crest cells of the hindbrain (arrows) and midbrain (arrowhead). XFD-7: neurula (stage 15) (PI, stage 35 (0) and stage 44 (R) embryos. Arrowhead (R) points at localized transcription in a defined area of the gut at the right side of the embryo XFD-9: Embryos at stage 16 (S), stage 25 (T). stage 35 [U] and transverse section through a stage 36 embryo [V] at the middle part. Arrowheads in (T) denote the border between segmented and unsegmented somitic mesoderm. arrowheads in (U) point at intense staining near the posterior pole XFD-l0: Neurula (stage 15) embryo [W]. lateral view of a neurula Istage 16) embryo [X] and dorsal view at an embryo at stage 24/25 (Y). Arrowheads in (V) point at a cranial neural crest cells. b, blastocoel; bp, blastoporus; d and v, dorsal and ventral lip of blastoporus; f, neural floor plate; g, foregut; h, heart; n, notochord; p, pronephros.