Enforced expression of the transcription factor HOXD3 under the control of the Wnt1 regulatory element modulates cell adhesion properties in the developing mouse neural tube.

HOX genes expressed in a specific spatial and temporal manner play a crucial role in determining the body plan during the early development of vertebrates. In adult tissues, many HOX genes participate in normal hematopoiesis and carcinogenesis. We previously found that overexpression of the homeobox gene HOXD3 alters expression levels of cell adhesion molecules in human cancer cell lines. Here, we have investigated whether HOXD3 expression is related to the cell adhesion processes during mouse development focusing on dorsal midline cells or roof-plate cells of the neural tube and neural crest cells. We created transgenic mouse embryos, in which HOXD3 is expressed in the dorsal midline under the control of the Wnt1 regulatory element, and analyzed these embryos at embryonic day 10.5-13.5. In HOXD3-expressing transgenic embryos, although neural crest-derived structures in the trunk region appeared to be normal, striking abnormalities were found in the neural tube. In transgenic embryos expressing the lacZ gene under the control of the Wnt1 regulatory element, expression of lacZ was restricted to roof-plate cells within the neural tube. By contrast, in HOXD3-expressing transgenic embryos, expression of HOXD3 was not only located in the dorsal neural tube, but also had spread inside the ventricular zone in more ventral regions of the neural tube. These findings show that the HOXD3 transgene is expressed more broadly than the Wnt1 gene is normally expressed. Expression of both Wnt1 and Msx1, marker genes in the roof plate, was further extended ventrally in HOXD3-expressing embryos than in normal embryos, suggesting that expression of the HOXD3 transgene expands the roof plate ventrally within the neural tube. In the ventricular zone of HOXD3-expressing embryos at embryonic day 10.5, we observed an increase in the number of mitotic cells and failure of interkinetic nuclear migration of progenitor cells. Furthermore, in HOXD3-expressing embryos at embryonic day 12.5, the ventricular zone, in which progenitor cells became more loosely connected to each other, was composed of a large number of cells that did not express N-cadherin. Our results indicate that expression of HOXD3 is closely associated with modulation of cell-adhesive properties during embryonic development.

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