An evolutionary conserved element is essential for somite and adjacent mesenchymal expression of the Hoxa1 gene

Abstract

The murine Hoxa1 gene is a member of the vertebrate Hox complex and plays a role in defining the body plan during development. At day 8.0-9.0 post coitus, Hoxa1 transcripts are detected extensively throughout the embryo in the neural tube, adjacent mesenchyme, paraxial mesoderm, somites and gut epithelium; expression extends from the most caudal region of the embryo to the rhombomere 3/4 border. This spatiotemporal expression of Hoxa1 mRNA is critical for normal embryonic development. We have previously identified a 10 bp element, called CE2, which is located approximately 3 kilobases 3' of the Hoxa1 coding region in the RAIDR5 enhancer, and which binds to an approximately 170 kd protein in retinoic acid treated P19 embryonal carcinoma cells. CE2 elements were also identified 3' of the murine Hoxb1 gene, the chicken Hoxb1 gene and the human Hoxa1 gene. To examine the role of this CE2 element in regulating Hoxa1 expression in vivo, transgenic mice were generated which express a Hoxa1 beta-galactosidase reporter gene that contains a mutation in the CE2 element. Relative to transgenic mice bearing a wild type CE2 element, the mutant CE2 construct recapitulated rhombomeric, neural, and gut epithelium expression but failed to show beta-galactosidase expression in somites and adjacent mesenchymal tissue. Gel shift analysis showed that binding activity similar to that detected in extracts prepared from retinoic acid treated P19 cells was present in nuclear extracts prepared from day 9.0 embryos. However, an additional binding complex not detected in P19 cells was also observed. These results indicate that in transgenic animals, the evolutionary conserved CE2 element is a somite and adjacent mesenchymal enhancer of Hoxa1 expression.

Dynamic regulation of Nanog and stem cell-signaling pathways by Hoxa1 during early neuro-ectodermal differentiation of ES cells

“…4A). CE2 and the RARE have been previously shown to have regulatory activity in assays where large genomic fragments from the Hoxa1 locus were tested in transgenic mouse reporter assays (29,38). In addition, the RARE has been mutated in the endogenous Hoxa1 locus and shown to be required for early expression (27).…”

Retinoid Regulated Association of Transcriptional Co-regulators and the Polycomb Group Protein SUZ12 with the Retinoic Acid Response Elements of Hoxa1, RARβ2, and Cyp26A1 in F9 Embryonal Carcinoma Cells

“…69,70 For example, the Hoxa1 enhancer contains an evolutionarily conserved element (CE2) that is required for expression of Hoxa1 in certain tissues, and is located adjacent to the Hoxa1 RARE. 71 Thus, it is likely that the recruitment of co-regulators to regulatory elements is influenced by the binding of transcription factors to neighboring regulatory elements.…”

Facial dysgenesis: A novel facial syndrome with chromosome 7 deletion p15.1‐21.1

“…This was a reasonable consideration because the HOXA gene cluster is found near the centromeric end of this patient's deletion at 7p15. The HOXA genes encode transcription factors that are essential for proper direction of somatic development [Morrison, 1998; Thompson et al, 1998]. The 13 components of the HOXA gene family are oriented in a telomere to centromere direction on the short arm of chromosome 7 and are expressed in a cephalad to caudad direction on the developing fetus.…”