Developmental and spatial patterns of expression of the mouse homeobox gene, Hox 2.1

The Hox 2.1 gene forms part of a cluster of homeobox-containing genes on mouse chromosome 11. Analysis of Hox 2.1 cDNAs isolated from an 8 1/2-day p.c. mouse embryo library predicts that the gene encodes a 269 amino acid protein (Mr, 29,432). This deduced protein contains a homeobox 15 amino acids from the carboxy terminus and is very rich in serine and proline. A second partially conserved region present in several other genes containing homeoboxes, the hexapeptide Ile-Phe-Pro-Trp-Met-Arg, is located 12 amino acids upstream of the homeodomain and is encoded by a separate exon. Analysis of Hox 2.1 gene expression reveals a complex and tissue-specific series of RNA transcripts in a broad range of fetal tissues (lung, spinal cord, kidney, gut, spleen, liver and visceral yolk sac). Comparison of the temporal patterns of gene expression during development and in the adult suggests that Hox 2.1 is regulated independently in different tissues. Evidence is also presented that transcripts from other loci have extensive homology to the Hox 2.1 gene in sequences outside of the homeobox. In situ hybridization shows that Hox 2.1 transcripts are regionally localized in the spinal cord in an apparent anterior-posterior gradient extending from the hind brain. The distribution of RNA also displays a cell-type specificity in the lung, where mesodermal cells surrounding the branching epithelial cell layer accumulate high levels of Hox 2.1 transcripts.