Differential and stage-related expression in embryonic tissues of a new human homoeobox gene

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Abstract
The homoeobox is a 183 base-pair (bp) DNA sequence1 conserved in several Drosophila genes controlling segmentation and segment identity2–4. Homoeobox sequences have been detected in the genome of species ranging from insects and anellids to vertebrates5,6 and homoeobox containing genes have been cloned from Xenopus7–9, mouse10–22 and man23. We recently isolated human homoeobox containing complementary DNA clones, that represent transcripts from four different human genes24. One clone (HHO.c10) is selectively expressed in a 2.1 kilobase (kb) polyadenylated transcript in the spinal cord of human embryos and fetuses 5–10 weeks after fertilization25. We report the characterization of a second cDNA clone, termed HHO.c13, that represents a new homoeobox gene. This clone encodes a protein of 255 amino-acid residues, which includes a pentapeptide, upstream of the homoeo domain, conserved in other Drosophila, Xenopus, murine and human homoeobox genes. By Northern analysis HHO.c13 detects multiple embryonic transcripts, which are differentially expressed in spinal cord, brain, backbone rudiments, limb buds and heart in 5–9-week-old human embryos and fetuses, in a striking organ- and stage-specific pattern. These observations suggest that in early mammalian development homoeobox genes may exert a wide spectrum of control functions in a variety of organs and body parts, in addition to the spinal cord.