Expression of Hox-2.4 homeobox gene directed by proviral insertion in a myeloid leukemia.

The presence of an altered Hox-2.4 gene in the WEHI3B murine myeloid leukemia suggests that homeobox genes may contribute to neoplasia. A survey of 31 leukemia cell lines of the myeloid, lymphoid and erythroid lineages revealed that Hox-2.4 was expressed only in WEHI3B and the pre-B lymphoid line 70Z/3, in which no DNA rearrangement was observed. To clarify the WEHI3B alteration and normal Hox-2.4 structure, we have sequenced near full length cDNA clones from WEHI3B and 70Z/3, and the 5' portion of the normal Hox-2.4 gene. A WEHI3B cDNA clone demonstrates that an intracisternal A-particle (IAP) provirus has inserted within the first exon of the gene and generated a Hox-2.4 mRNA with a 5' sequence derived from the IAP long terminal repeat. A remarkable degree of similarity found between the amino acid sequences of Hox-2.4 and Hox-3.1, which reside on different chromosomes, supports the notion that an ancient homeobox gene cluster has been duplicated and dispersed early in vertebrate evolution.     

Hox-4 gene expression in mouse/chicken heterospecific grafts of signalling regions to limb buds reveals similarities in patterning mechanisms.

The products of Hox-4 genes appear to encode position in developing vertebrate limbs. In chick embryos, a number of different signalling regions when grafted to wing buds lead to duplicated digit patterns. We grafted tissue from the equivalent regions in mouse embryos to chick wing buds and assayed expression of Hox-4 genes in both the mouse cells in the grafts and in the chick cells in the responding limb bud using species specific probes. Tissue from the mouse limb polarizing region and anterior primitive streak respecify anterior chick limb bud cells to give posterior structures and lead to activation of all the genes in the complex. Mouse neural tube and genital tubercle grafts, which give much less extensive changes in pattern, do not activate 5'-located Hox-4 genes. Analysis of expression of Hox-4 genes in mouse cells in the grafted signalling regions reveals no relationship between expression of these genes and strength of their signalling activity. Endogenous signals in the chick limb bud activate Hox-4 genes in grafts of mouse anterior limb cells when placed posteriorly and in grafts of mouse anterior primitive streak tissue. The activation of the same gene network by different signalling regions points to a similarity in patterning mechanisms along the axes of the vertebrate body.     

Mouse Hox-2.2 specifies thoracic segmental identity in Drosophila embryos and larvae

The mouse genome has a number of homeobox genes that are structurally similar to the Drosophila Antenapedia (Antp) gene. We find that one of the mouse Antp-like genes, Hox-2.2, when expressed in developing Drosophila cells under control of a heat shock promoter, can induce homeotic transformations that are nearly identical to those caused by ectopic expression of Antp. In larvae, the Hox-2.2-induced transformations include thoracic denticle belts in place of head structures; in adults, the Hox-2.2 transformations include thoracic legs in place of antennae. The phenotypic effects of Hox-2.2 do not depend on the endogenous Antp gene, whose spatial limits of expression are unaffected by Hox-2.2 expression. Thus, in the Drosophila embryo, Hox-2.2 can substitute for some of the segmental identity functions of Antp, presumably by regulating the same set of downstream genes.     

The murine genes Hox-5.1 and Hox-4.1 belong to the same HOX complex on chromosome 2

Two different loci of Antennapedia-related homeobox-containing genes have been shown to map to mouse chromosome 2: the HOX-5 complex and the Hox-4.1 gene. These independently derived loci are likely to be parts of a single gene complex, although their close linkage has not yet been demonstrated. Since cosmid walks to extend the HOX-5 cluster and to potentially link the two loci were unsuccessful, we have used large restriction fragments separated by pulsed-field gel electrophoresis to demonstrate the linkage between probes from the HOX-5 region and sequences near Hox-4.1. To further define the distance between the two linked loci, we screened a NotI jumping library with sequences near the Hox-5.1 gene to obtain a marker within the region predicted to contain Hox-4.1. The jumping endpoint lies within genomic clones from a lambda phage walk extending from the 5' end of Hox-4.1, and thus provides clear evidence of linkage between the two Hox loci. Our results demonstrate that Hox-4.1 lies approximately 35 kb downstream of the Hox-5.1 gene and that the two loci do indeed thus constitute parts of the same HOX complex.     

Sequence analysis of the murine Hox-2.2, -2.3, and -2.4 homeo boxes: evolutionary and structural comparisons

We have determined the nucleotide sequences and deduced the amino acid sequences of three tandemly arranged murine boxes of the Hox-2 homeo box gene complex on mouse chromosome 11 (Hox-2.2, -2.3, and -2.4). The type and position of differences with other sequenced homeo boxes were analyzed. Hox-2.2 is nearly identical with its cognate human homeo box Hu-2. Hox-2.3 shares 59 of 61 amino acids with the Antennapedia homeo domain of Drosophila and the MM-3 homeo domain of Xenopus and shows 60 of 61 amino acid identity with human HuC1. Hox-2.3, MM-3, and HuC1 also share a stretch of six glutamic acid residues followed by a stop codon 15-20 amino acids 3' of the homeo domain. Hox-2.4 is relatively divergent from most of the other homeo boxes sequenced to date; however, it matches the Hox-3.1 murine homeo domain at 60 of 61 positions. Sequence comparisons with other murine homeo domains, together with previous studies of their genomic organization and chromosomal location, provide support for the hypothesis of a large-scale duplication resulting in the two major murine homeo box gene complexes Hox-1 and Hox-2.