An unexpected feature of the large mammalian genome is the frequent occurrence of closely linked head-to-head gene pairs. Close apposition of such gene pairs has been suggested to be due to sharing of regulatory elements. We show here that the head-to-head gene pair encoding two small heat shock proteins, alphaB-crystallin and HspB2, is closely linked in all major mammalian clades, suggesting that this close linkage is of selective advantage. Yet alphaB-crystallin is abundantly expressed in lens and muscle and in response to a heat shock, while HspB2 is abundant only in muscle and not upregulated by a heat shock. The intergenic distance between the genes for these two proteins in mammals ranges from 645 bp (platypus) to 1069 bp (opossum), with an average of about 900 bp; in chicken the distance was the same as in duck (1.6 kb). Phylogenetic footprinting and sequence alignment identified a number of conserved sequence elements close to the HspB2 promoter and two farther upstream. All known regulatory elements of the mouse alphaB-crystallin promoter are conserved, except in platypus and birds. The lens-specific region 1 (LSR1) and the heat shock elements (HSEs) lack in birds; in platypus the LSR1 is reduced to a Pax-6 site, while the Pax-6 site in LSR2 and a HSE are absent. Most likely the primordial mammalian alphaB-crystallin promoter had two LSRs and two HSEs. In transfection experiments the platypus alphaB-crystallin promoter retained heat shock responsiveness and lens expression. It also directed lens expression in Xenopus laevis transgenes, as did the HspB2 promoter of rat or blind mole rat. Deletion of the middle of the intergenic region including the upstream enhancer affected the activity of both the rat alphaB-crystallin and the HspB2 promoters, suggesting sharing of the enhancer region by the two promoters.

We have only just begun to decipher the complexity of our brain, including its maturation. Correct brain development and communication among brain areas are crucial for proper cognitive behavior. Brain area-specific genes expressed within a particular time window direct neurodevelopmental events such as proliferation, migration, axon guidance, dendritic arborization, and synaptogenesis. These genes can pose as susceptibility factors in neurodevelopmental disorders eventually resulting in area-specific cognitive deficits. Therefore, in utero electroporation (IUE)-mediated gene transfer can aid in creating valuable animal models in which the regionality and time of expression can be restricted for the targeted gene(s). Moreover, through the use of cell-type-specific molecular constructs, expression can be altered in a particular neuronal subset within a distinct area such that we are now able to causally link the function of that gene in that brain region to the etiology of the disorder. Thus, IUE-mediated gene transfer is an attractive molecular technique to spatiotemporally address the developmental aspects of gene function in relation to neurodevelopmental disorder-associated endophenotypes.

Recently we found that the human papillary renal cell carcinoma-associated protein PRCC interacts with the cell cycle control protein Mad2B, and translocates this protein to the nucleus where it exerts its mitotic checkpoint function. Here we have succesfully isolated Xenopus laevis Mad2B and PRCC cDNAs. The full-length xMad2B cDNA encodes a 211 amino acid protein that is highly homologous to human Mad2B, thus pointing to an important function for this protein in higher eukaryotes. The full-length xPRCC cDNA encodes a 544 amino acid protein. Remarkably, this protein contains an amino-terminal region distinct from that in mouse and human, whereas the C-terminal region is highly conserved. Northern blot and RT-PCR analyses revealed a relatively low expression of both xMad2B and xPRCC in most tissues examined. However, an abundant expression was observed in testis and oocyte, indicating a role in meiotic division processes. Coimmunoprecipitation and immunofluorescence analyses revealed that, despite its distinct amino terminus, the xPRCC-protein is still capable of interacting with xMad2B and of shuttling this protein to the nucleus. Therefore, the well-established animal model Xenopus laevis can be used as a powerful system to study in detail the role of xPRCC and xMad2B in the intricate processes of cell cycle control.

Genetic sequences encoding the novel pituitary polypeptide 7B2 were isolated from a human pituitary cDNA library. Hybridization analysis of a panel of human × mouse cell hybrids with a 7B2 cDNA probe indicated that the locus for the human 7B2 gene is probably located on chromosome 15. In situ hybridization analysis of metaphase chromosomes allowed the regional localization of the 7B2 gene to chromosome 15 at q13→q14.

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