Several mouse and human genes encoding the DNA‐binding homeobox domain are implicated here in haematopoiesis, a differentiation process maintained throughout life. Four homeobox cDNA clones were isolated from bone marrow and spleen of adult mice and two from the human leukaemia cell line K562. They derive from the Hox 1.1, Hox 2.3, Hox 6.1 genes and two previously undescribed genes, one of a type (paired) not found before in vertebrates. A survey of 36 cell lines of the lymphoid, myeloid and erythroid lineages revealed that certain homeobox transcripts were almost ubiquitous, while others were restricted to certain lineages or even particular cell lines. The expression pattern altered in a myeloid and an erythroid line induced to terminal differentiation, and in novel lines that had switched from a lymphoid to a myeloid phenotype. Altogether, the haemopoietic compartment may contain up to 20 homeobox transcripts. In one myeloid leukaemia, DNA rearrangement has perturbed expression. These findings suggest that homeobox genes may influence developmental decisions within the haemopoietic system.
Genomic changes within chromosome band 11p13 appear to have a role in the initiation of Wilms' tumour. The human Harvey ras oncogene, c-Ha-ras 1, has been located by Jhanwar et al. immediately adjacent to this region at band 11p14 .1, although several groups have assigned the gene more distally at band 11p15 . We have examined tumour DNA from two cases of sporadic Wilms' tumour, and report here that in both cases one of the two constitutional c-Ha-ras 1 alleles was absent. One tumour had a reciprocal translocation between the short arm of chromosome 11 (at band 11p13), and the long arm of chromosome 12, with no visible loss of chromosomal material. The loss of a c-Ha-ras 1 allele in association with this translocation indicates that a submicroscopic deletion had occurred. The resulting hemizygosity may have had a role in tumour initiation. Our results indicate that the c-Ha-ras 1 gene and the 'Wilms' tumour locus' may be in close proximity. It would, therefore, be premature to exclude the possibility that these two sites are functionally related.
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