Abstract
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 Xebl (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 
and 
of gestation and in extraembryonic tissues at day 
. 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-
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-
embryos, and in the posterior mesoderm and ectoderm of day-8) 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.
The locus has been designated according to the nomenclature system accepted by the International Committee for Standardized Genetic Nomenclature and agreed with T. Roderick, Jackson Laboratory.
