Pohl BS and Knöchel W (2005), Of Fox and Frogs: Fox (fork head/winged helix) ...

XB-ART-2456

Gene 2005 Jan 03;344:21-32. doi: 10.1016/j.gene.2004.09.037.

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Of Fox and Frogs: Fox (fork head/winged helix) transcription factors in Xenopus development.

Pohl BS , Knöchel W .

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Transcription factors of the Fox (fork head box) family have been found in all metazoan organisms. They are characterised by an evolutionary conserved DNA-binding domain of winged helix structure. In the South African clawed frog, Xenopus laevis, more than 30 Fox genes have been found so far. This review summarises our present knowledge regarding the general structure and common features of the fork head box and will then characterise Fox genes that have been described in Xenopus. Special attention was paid to the temporal and spatial expression patterns during early embryonic development. For some of these genes, the molecular mechanisms leading to their regulation after the onset of zygotic transcription are known. We also report on functional aspects including target gene regulation, cell or tissue specification and interference with the cell cycle. Finally, Fox proteins serve as mediators of signalling pathways and they might function as checkpoint molecules for the cross-regulatory interactions of different intracellular signal transduction chains.

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Species referenced: Xenopus laevis
Genes referenced: foxa1 foxa2 foxa4 foxb1 foxb2 foxc1 foxc2 foxd1 foxd2 foxd3 foxd4l1.1 foxe1 foxe3 foxg1 foxh1 foxh1.2 foxi1 foxi4 foxj1 foxj1.2 foxk2 foxl1

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	Fig. 1. Schematic presentation of the Fox protein family in X. laevis. The coloured boxes represent the fork head domains (in identical colours as in Fig. 2). bAQ marks an acidic domain and bSIMQ denotes a Smadinteracting motif (see text). White triangles represent the position of exon/intron boundaries within the corresponding gene. Plus (+) and minus () indicate transactivating or transrepressing functions, respectively (Bolce et al., 1993; Dirksen and Jamrich, 1995; El-Hodiri et al., 2001; Gamse and Sive, 2001; King and Moore, 1994; Klein et al., 2002; Kfster et al., 1998; Lef et al., 1996; Pohl and Knfchel, 2002; Pohl et al., 2002).
	Fig. 2. Alignment of the predicted amino acid sequences of 31 X. laevis fork head domains to that of the Drosophila fkh gene. Coloured residues are those divergent from Drosophila fkh. The architecture of the domain is shown on top, with H=a-helix, S=h-sheet, and W=wing. At the bottom, the all-over conserved residues are marked by asterisks. The nuclear localisation signal as determined for FoxA2 is underlined.
	Fig. 3. Temporal and spatial expression patterns of Xenopus Fox genes. The temporal profile, as obtained by RT-PCR from different developmental stages, is shown on the left side. On the right side, the spatial expression pattern is shown at the gastrula, neurula, and early tadpole stages.