Temporal and spatial expression patterns of FoxN genes in Xenopus laevis embryos

Abstract

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...

FOXR2 Interacts with MYC to Promote Its Transcriptional Activities and Tumorigenesis

“…However, unlike FOXR2, FOXR1 protein was not detectable in any breast, liver, or lung cell lines we tested by MS or Western analysis ( Figure 1D ). These data suggest that FOXR2 is likely a protooncogene in these cancers, while FOXR1 expression may be more restricted to early stages of development as previously reported (Schuff et al, 2006). …”

Oncogenic activation of FOXR1 by 11q23 intrachromosomal deletion-fusions in neuroblastoma

“…This indicated that the promoters of these genes may indeed be driving the observed ALL (92) Glioma (153) Breast (351) Cervix (36) Colon (315) Renal (47) Endometrium (209) Lung (121) Other (296) Figure 1b). This is consistent with previous findings that FOXR1 expression is only detectable in the early stages of embryogenesis (Katoh and Katoh, 2004a, b;Schuff et al, 2006). To further explore the extent of FOXR1 expression in neuroblastoma, we performed quantitative (qPCR) on an additional 362 neuroblastoma tumor samples and identified three more tumors exhibiting very high FOXR1 expression (Table 1).…”

“…On the basis of sequence alignment, FOXR1 is most similar to the FOXP sub-family (Myatt and Lam, 2007). FOXR1 expression is restricted to the early stages of embryogenesis as is its ortholog FOXR2 (FOXN6), which is located on the X chromosome (Katoh and Katoh, 2004a, b;Schuff et al, 2006).…”

Chromosome 11q23 aberrations activating FOXR1 in B-cell lymphoma

“…5, 6 Ectopic expression as result of 11q23 intrachromosomal deletion-fusion has hitherto been described in neuroblastoma only. 7 In-frame fusions with the 5′ MLL or PAFAH1B2 genes led to overexpression of FOXR1 .…”