Isolation and expression of a new mouse homeobox gene.

A homeobox-containing clone has been isolated from an adult mouse kidney cDNA library and shown by DNA sequence analysis to be a new isolate, Hox-6.1. A genomic clone containing Hox-6.1 has been isolated and found to contain another putative homeobox sequence (Hox-6.2), within 7 kb of Hox-6.1. In situ hybridization of mouse metaphase chromosomes shows this Hox-6 locus to be located on chromosome 14 (14E2). Hox-6.1 has been studied in detail and the predicted protein sequence of the homeobox is 100% homologous to the Xenopus Xeb1 (formally AC1) homeobox and the human c8 homeobox (Carrasco et al. 1984; Boncinelli et al. 1985; Simeone et al. 1987). Southern blotting shows that the DNA sequence encoding Hox-6.1 is single copy. Expression of Hox-6.1 has been studied in adult tissues and embryos by RNase protection assays, Northern blotting analysis and in situ hybridization. RNase protection assays show that Hox-6.1 transcripts are present in embryos between days 9 1/2 and 13 1/2 of gestation and in extraembryonic tissues at day 9 1/2. Adult expression is detectable in kidney and testis but not in liver, spleen and brain. One major transcript is detectable on Northern blots of kidney and day-13 1/2 embryo RNA. In kidney, this transcript is 2.7 kb whereas in embryos the major transcript is smaller at 1.9 kb, a much fainter band being visible at 2.7 kb. Localized expression of Hox-6.1 is observed in the spinal cord and prevertebral column of day-12 1/2 embryos, and in the posterior mesoderm and ectoderm of day-8 1/4 embryos. An anterior boundary of expression is located just behind the hindbrain whereas the boundary in the mesoderm is located at the level of the 7th prevertebra.