Pescadillo is a multifunctional, nuclear protein involved in rRNA precursor processing, ribosomal assembly, and transcriptional regulation. Pescadillo has been assigned important functions in embryonic development and tumor formation. We previously identified pescadillo as a potential downstream target of non-canonical Wnt-4 signaling. Here we have investigated for the first time the function of the Xenopus laevis homolog of pescadillo during early embryogenesis on a molecular level. Loss of function analysis indicates that pescadillo is required for eye development and neural crest migration. BrdU incorporation and TUNEL assays indicate that a loss of pescadillo function affects proliferation and triggers apoptosis through a p53-mediated mechanism. Furthermore, pescadillo affects the expression of early eye-specific marker genes, likely independent of its function in regulating proliferation and apoptosis, and in addition migration of cranial neural crest cells. Our data indicate that pescadillo has multiple important functions during X. laevis development and that its function is highly conserved among different species.

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Using RT-PCR and in situ hybridisation, we have analysed the temporal and spatial expression patterns of Xenopus Fox genes of subclass N. By screening cDNA libraries and by RT-PCR using embryonic RNA and primers derived from EST analyses, we could isolate FoxN2, FoxN4, FoxN5 and different isoforms of FoxN3. FoxN2 and FoxN3 transcripts were found during all developmental stages including early cleavage and tailbud stages. FoxN5 transcripts were only present at early cleavage stages, while FoxN4 expression began after midblastula transition. Spatial expression of FoxN2 was first detected in the early eye field and later, in the branchial arches, the vagal ganglion and in the developing retina. FoxN3 transcripts were found within the animal cap. In post-gastrula embryos, neural crest cells and the early eye field showed strong expression of FoxN3. At late tadpole stages, the branchial arches were stained. FoxN4 was expressed in the early eye field and later in the developing retina cells, the nephrostomes of the pronephric kidney and in the midbrain. A ubiquitous expression of FoxN5 was found in early cleavage stage embryos. KEY WORDS: X. laevis, FoxN transcription factor, eye anlage, nephrostome, branchial archForkhead box (Fox) transcription factors are involved in a variety of biological processes, such as cell proliferation, maintenance of pluripotency and cellular differentiation. According to conserved amino acid positions within the DNA binding winged-helix domain, they are divided into subclasses (FoxA -FoxS) (Kaestner et al., 2000). Subclass N gained special interest, because Foxn1 (whn) was found to be mutated in nude mice lacking immune defence (Nehls et al., 1994). Foxn1 knockout in mice results in downregulation of hair keratins, athymia and abnormal morphogenesis of the epidermis and hair follicles. Furthermore, Foxn1 is a downstream target of the Wnt pathway (Balciunaite et al., 2002). FOXN2/HTLF (Human T-cell Leukemia Factor) was identified in search of transcription factors binding the LTR of the human T-cell leukemia virus (Li et al., 1992). FOXN3/CHES1 (checkpoint suppressor 1) suppresses the lethality, UV sensitivity and a G2 checkpoint defect of a mec1 null mutation in yeast and plays an essential role in cell cycle regulation (Pati et al., 1997;Scott et al., 2003). It was found to be downregulated in oral squamous cell carcinoma (OSCC) (Chang et al., 2005). Foxn4 is expressed in the retina (Gouge et al., 2001). A knockout analysis in mice revealed that Foxn4 is involved in the development of amacrine and horizontal cells during retinogenesis. The retinogenic factors Math3, NeuroD1 and Prox1 have been identified as putative downstream targets (Li et al., 2004). FOXN5/R1, FOXN6/R2 and Int. J. Dev. Biol. 50: 429-434 (2006) doi: 10.1387/ijdb.052126ms their homologues in the rat and the mouse were identified in silico. It is known that human FOXN6 RNA is expressed in breast cancer cell lines and primary breast cancer (Katoh and Katoh, 2004a;2004b).While the information on mammalian Fox...

We here describe the sequences and expression patterns of three new Fox (fork head box) transcription factors in Xenopus laevis embryos. xlFoxI2, another member of subclass I, is maternally transcribed. Zygotic transcripts are first detected during neurulation and become localised to the dorsal part of epibranchial placodes. xlFoxM1 like xlFoxP1 are the first members of subclasses M and P described in Xenopus. Both genes are maternally expressed and transcripts are found during early cleavage stages in the animal blastomeres. xlFoxM1 is strongly upregulated during neurula stages and transcripts are localised in the neuroectoderm. Later, expression is found in the spinal cord, the rhombencephalon, the retina and in the branchial arches. xlFoxP1 is activated during organogenesis and is mainly expressed in the brain, head mesenchyme and in the splanchnic layer of the lateral plate mesoderm. KEY WORDS: X. laevis, embryogenesis, fork head/winged helix factor, expression patternFox (fork head box) transcription factors are involved in various signalling pathways and cell fate decisions throughout development. According to conserved amino acid residues at distinct positions within the winged helix domain, these factors are categorised into the subclasses A to Q (Kaestner et al., 2000).While for the mouse and human species, Fox family members from all subclasses have been reported, in the South African clawed frog, Xenopus laevis, currently only the subclasses A to L are known. Here we report the sequence and initial characterisation of two additional Xenopus laevis Fox gene family members, xlFoxM1 and xlFoxP1 and add xlFoxI2 as a new member to the already existing subclass I. We describe the full length cDNAs encoding these proteins and investigate the temporal and spatial expression patterns of corresponding genes by RT-PCR and by whole mount in situ hybridisations. Results and Discussion xlFoxI2The FoxI subclass is already known in different organisms to contain several members and has recently been analysed regarding the phylogenetic relationship inside the subclass based on the zebrafish members (Solomon et al., 2003). By searching in EST data bases we have found an IMAGE-clone (4084049), which covers the complete translated region of a FoxI subclass member in Xenopus laevis. Referring to the suggested terminology regardInt.

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