The NK homeobox gene cluster predates the origin of Hox genes

Hox and other Antennapedia (ANTP)-like homeobox gene subclasses - ParaHox, EHGbox, and NK-like - contribute to key developmental events in bilaterians [1-4]. Evidence of physical clustering of ANTP genes in multiple animal genomes [4-9] suggests that all four subclasses arose via sequential cis-duplication events. Here, we show that Hox genes' origin occurred after the divergence of sponge and eumetazoan lineages and occurred concomitantly with a major evolutionary transition in animal body-plan complexity. By using whole genome information from the demosponge Amphimedon queenslandica, we provide the first conclusive evidence that the earliest metazoans possessed multiple NK-like genes but no Hox, ParaHox, or EHGbox genes. Six of the eight NK-like genes present in the Amphimedon genome are clustered within 71 kb in an order akin to bilaterian NK clusters. We infer that the NK cluster in the last common ancestor to sponges, cnidarians, and bilaterians consisted of at least five genes. It appears that the ProtoHox gene originated from within this ancestral cluster after the divergence of sponge and eumetazoan lineages. The maintenance of the NK cluster in sponges and bilaterians for greater than 550 million years is likely to reflect regulatory constraints inherent to the organization of this ancient cluster.     

Expression of the homeobox gene,Hox 2.1, during mouse embryogenesis

This article reviews recent studies on the expression of the homeobox gene, Hox 2.1, during mouse embryogenesis, using the technique of in situ hybridization. Differential hybridization of radiolabelled antisense versus sense strand RNA is first clearly detected in sections of 8.5 day post coitum (p.c.) early somite embryos. At 12.5 days p.c., higher levels of Hox 2.1 expression are seen in the spinal cord, extending into the base of the hind brain. Hybridization of antisense Hox 2.1 RNA is also seen in the spinal ganglia, in the nodose ganglia of the Xth cranial nerve (which contains derivatives of the neural crest arising from the posterior hind brain), and in the myenteric plexus. Mesodermal cells of certain visceral organs also express Hox 2.1 RNA, in particular the mesoderm of the lung, stomach and meso- and meta-nephric kidney. Comparison of the spatial domains of expression of mouse homeobox genes reveals a pattern consistent with the idea that they play a role in anteroposterior positional specification during embryogenesis.     

A mouse homeobox containing gene on chromosome 11: sequence and tissue-specific expression.

We have molecularly cloned a mouse homeobox containing gene by isolating cDNA and genomic clones. The gene is located in a previously described cluster on chromosome 11 (Hart et al. (1985) Cell 43, 9-18) and was identified as the Hox2.3 gene. We present the complete mRNA sequence of this gene and describe similarities to other homeobox containing genes, among which its human homologue, the cl gene. High expression of the Hox2.3 gene was found in kidney, testis, and spinal cord of adult mice, in the spinal cord of 12.5-17.5 day embryos and in differentiating EC cells depending on their treatment. Three different treatments of the pluripotent EC cell line P19, each leading to the induction of a specific differentiation pathway, resulted in all cases in induction of Hox2.3; however, major quantitative differences in this response were observed.     

Structure and sequence of the human homeobox gene HOX7.

A cosmid containing the human sequence HOX7, homologous to the murine Hox-7 gene, was isolated from a genomic library, and the positions of the coding sequences were determined by hybridization. DNA sequence analysis demonstrated two exons that code for a homeodomain-containing protein of 297 amino acids. The open reading frame is interrupted by a single intron of approximately 1.6 kb, the splice donor and acceptor sites of which conform to known consensus sequences. The human HOX7 coding sequence has a very high degree of identity with the murine Hox-7 cDNA. Within the homeobox, the two sequences share 94% identity at the DNA level, all substitutions being silent. This high level of sequence similarity is not confined to the homeodomain; overall the human and murine HOX7 gene products show 80% identity at the amino acid level. Both the 5' and 3' untranslated regions also show significant similarity to the murine gene, with 79 and 70% sequence identity, respectively. The sequence upstream of the coding sequence of exon 1 contains a GC-rich putative promoter region. There is no TATA box, but a CCAAT and numerous GC boxes are present. The region encompassing the promoter region, exon 1, and the 5' region of exon 2 have a higher than expected frequency of CpG dinucleotides; numerous sites for rare-cutter restriction enzymes are present, a characteristic of HTF islands.     

Low level of Hox1.3 gene expression does not preclude the use of promoterless vectors to generate a targeted gene disruption. off.

A variety of experimental approaches have been devised recently to mutate mammalian genes by homologous recombination. In this report, we describe the disruption of the Hox1.3 locus by using two of these approaches, namely, positive-negative selection and activation of a promoterless gene. Interestingly, we observe similarly high frequencies of targeted disruption with both procedures. The high frequency of targeted disruption with a promoterless vector was unexpected given the extremely low level of Hox1.3 expression in the embryonic stem cell line used for these studies. These data indicate that minimal expression of the target gene is required to enrich for homologous recombination events with promoterless vectors and thus enhance the promoterless gene approach as a general strategy to mutate mammalian genes by homologous recombination.     

Coding sequence and flanking regions of the mouse vimentin gene

Summary Using a polyclonal antibody, a cDNA clone coding for part of mouse vimentin was identified in a gt11 expression library. DNA from this clone was used to screen a genomic library from Ehrlich Ascites Tumor cells for the mouse vimentin gene. A clone was found which contained the whole coding sequence and a large part of the 5- and 3-untranslated sequences. It was used to prepare a construct equivalent to a full-length cDNA clone. Extensive homologies to the vimentin sequence from other species were found for the coding and 3-untranslated sequences and the promoter region.