Article Abstract:
Homeosis, the partial or complete identity transformation of a body segment into that of another, was studied in mice with two Hoxb-4 mutations. Two skeletal changes resulted in the disruption of the first exon of hoxb-4'. The first skeletal change is a partial homeotic transformation of the atlas and the axis while the second deformity is defective closure of the sternum. These phenotypes have incomplete penetrance and variable expressivity with the sternum defect completely penetrant in the inbred background.
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Article Abstract:
The expression of rhombomere 4 (r4) is brought about by an autoregulatory cofactor dependent feedback mechanism and extradenticle (exd) homeodomain protein or its vertebrate homolog (pbx) act as cofactors in cooperation with Hoxb-1. The hindbrain of vertebrates is an organized structure with cellular compartments referred as rhombomeres, and Hox genes are involved in regulation of the structure. Hoxa-1 or Hoxb-1 expression is controlled by autoregulation mediated by labial proteins.
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Article Abstract:
An investigation on the role of the transcription factors Krox20 zinc finger gene and HoxB2 homeobox gene in the morphological segmentation of the hindbrain is presented. Time course HoxB2 expression experiments demonstrate that the gene is upregulated in rhombomeres (r) 3, 4 and 5 to high levels during early segmentation. The Krox20 enhancer element was identified and found to directly regulate the HoxB2 gene during hindbrain segmentation.
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