Close linkage of retinoic acid receptor genes with homeobox- and keratin-encoding genes on paralogous segments of mouse chromosomes 11 and 15

Linkage of the nuclear hormone receptor genes NR1D2, THRB, and RARB: evidence for an ancient, large-scale duplication

The THRA gene encoding thyroid hormone receptor alpha shares an unusual partial overlap with the NR1D1 gene encoding the orphan receptor Rev-ErbAalpha. Though THRA and NR1D1 have close relatives in THRB and NR1D2, which encode TRbeta and Rev-ErbAbeta, these beta isoforms do not share an analogous overlap. Here we report that the human THRB and NR1D2 genes are separated by approximately 1 Mb on chromosome 3 and that these two genes are also linked to the RARB gene, which encodes retinoic acid receptor beta. Since previous results indicate that the THRA/NR1D1 locus is also linked to the RARA gene, these results suggest that the two receptor gene clusters were generated by a single large-scale duplication.

A new mutation Rim3 resembling Re(den) is mapped close to retinoic acid receptor alpha (Rara) gene on mouse chromosome 11

A new mouse mutation, recombination-induced mutation 3 (Rim3), arose spontaneously in our mouse facility. This mutation exhibits corneal opacity as well as abnormal skin and hair development resembling rex denuded (Re(den)) and bareskin (Bsk). Large-scale linkage analysis with two kinds of intersubspecific backcrosses revealed that Rim3 is mapped to the distal portion of Chromosome (Chr) 11, in which Re(den) and Bsk have been located, and is very close to the retinoic acid receptor, alpha (Rara). The genes, keratin gene complex-1, acidic, gene 10, 12 (Krt1-10, 12), granulin (Grn), junctional plakoglobin (Jup) and Rara, all of which regulate growth and differentiation of epithelial cells, are genetically excluded as candidate genes for Rim3, but are clustered in the short segment on mouse Chr 11.

The role of keratin proteins and their genes in the growth, structure and properties of hair

The importance of wool in the textile industry has inspired extensive research into its structure since the 1960s. Over the past several years, however, the hair follicle has increased in significance as a system for studying developmental events and the process of terminal differentiation. The present chapter seeks to integrate the expanding literature and present a broad picture of what we know of the structure and formation of hair at the cellular and molecular level. We describe in detail the hair keratin proteins and their genes, their structure, function and regulation in the hair follicle, and also the major proteins and genes of the inner and outer root sheaths. We discuss hair follicle development with an emphasis on the factors involved and describe some hair genetic diseases and transgenic and gene knockout models because, in some cases, they stimulate natural mutations that are advancing our understanding of cellular interactions in the formation of hair.

Expression of the homeobox gene HOXC4 in keratinocytes of normal skin and epithelial skin tumors is correlated with differentiation

Homeobox (HOX) genes share a highly conserved 183-bp sequence. The encoded proteins are capable of binding to specific DNA sequences and functioning as transcription factors. HOX genes play a critical role in the temporal and spatial differentiation of cells during embryogenesis. In several adult tissues, HOX genes are expressed in a constant, tissue-specific pattern, whereas in malignant tumors of these tissues an altered expression pattern was found. We investigated the expression of HOXC4 in adult normal skin by reverse-transcription polymerase chain reaction and non-radioactive RNA in situ hybridization. Moreover, HOXC4 expression was studied in various epidermal neoplasms (solar keratosis, six specimens; Bowen's disease, four; squamous cell carcinoma, nine; basal cell carcinoma, three) by RNA in situ hybridization. HOXC4 was found to be expressed in the suprabasal layers of the epidermis in normal skin specimens and the adjacent non-lesional epidermis of all other specimens. Atypical keratinocytes of solar keratoses and Bowen's disease as well as basaloid cells of basal cell carcinomas were negative. In squamous cell carcinoma, well differentiated areas with keratinization showed HOXC4 expression, whereas poorly differentiated areas were negative. Immunostaining with an antibody against cytokeratin 10, a marker of epidermal differentiation, was performed. A good correlation between the distribution pattern of HOXC4 and cytokeratin 10 in the lesions examined was found. These results suggest that HOXC4 is expressed mainly in differentiated keratinocytes. Lack of differentiation (as in neoplastic cells) is accompanied by downregulation of HOXC4 expression.

Mouse centromere mapping using oligonucleotide probes that detect variants of the minor satellite

Cytologically, the centromere is found at the very end of most Mus musculus chromosomes, co-localizing with an array of minor satellite sequences. It is separated from the euchromatin of the long arm by a large domain of heterochromatin, composed in part of arrays of major satellite sequences. We used oligonucleotide probes that specifically detect regions of sequence variation found in certain cloned minor satellite sequences. They detect a limited subset of the minor satellite arrays in the mouse genome, based on both pulsed-field gel electrophoresis and in situ hybridization data, and provide direct molecular genetic markers for individual centromeres in some inbred mouse strains. Array size polymorphisms detected by these probes map to positions consistent with the centromeres of chromosomes 1 and 14 in the BXD recombinant inbred (RI) strains. The genetic distances between these minor satellite arrays and loci on the long arms of chromosomes 1 and 14 are consistent with repression of meiotic recombination in the heterochromatic domains separating them. The existence of chromosome-specific minor satellite sequences implies that the rate of sequence exchange between non-homologous chromosomes relative to the rate between homologous chromosomes is much lower than has previously been postulated. We suggest that the high degree of sequence homogeneity of mouse satellite sequences may instead reflect recent common ancestry.

The complete sequence of the gene encoding mouse cytokeratin 15

To characterize the type-I keratin-encoding gene family around the mouse keratin 19-encoding gene (K19, EndoC), which encodes simple epithelial-type cytokeratin (CK), we screened a mouse genomic library by hybridization to a K19 cDNA probe. One clone of 16 kb contained the second to the sixth exons of K19 and the other keratin-encoding gene was located about 4 kb downstream from K19. Sequencing, Northern hybridization and genomic Southern blotting revealed that the downstream gene encodes the mouse K15 gene. This gene consists of eight exons and the positions of the introns coincide with those of other type-I keratin-encoding genes. The 5' upstream regions of the mouse and human K15 genes contain homologous sequences around the respective TATA boxes, suggesting that the same factors are involved in the regulation of their transcription.

A genetic linkage map of the mouse: current applications and future prospects

Technological advances have made possible the development of high-resolution genetic linkage maps for the mouse. These maps in turn offer exciting prospects for understanding mammalian genome evolution through comparative mapping, for developing mouse models of human disease, and for identifying the function of all genes in the organism.

Homeobox genes and skin development: a review

Homeobox (HOX) genes are a gene family that encode information critical for the normal embryologic development of many different organisms, including vertebrates. HOX genes encode transcriptional regulatory factors that bind to multiple different genes and thereby determine the developmental fate of a cell. The role of HOX genes in the development of skin is undetermined but, based on information from other organisms and recent experimental data from skin models, it is likely that this class of genes is important for the normal development of skin adnexae, pigmentary system, and stratified epidermis during embryogenesis. The purpose of this review is to briefly summarize what is known about HOX genes and to familiarize the reader with recent insights into how HOX genes may function in skin development.

Mapping of the mouse Rar loci encoding retinoic acid receptors RAR alpha, RAR beta and RAR gamma

Nuclear retinoic acid receptors RAR alpha, RAR beta and RAR gamma are transcription factors that bind all-trans retinoic acid as their ligand and mediate its action by activating particular set of genes that contain retinoic acid responsive elements in their promoter-enhancers. We have mapped genetic loci for these genes using restriction fragment length variants (RFLVs) in interspecific backcross mice. None of the Rar loci cosegregated with each other or with the new subclass of retinoid receptors, Rxr loci. Rara mapped to mChr 11, Rarb mapped to mChr 14, and Rarg mapped to mChr 15. The results are consistent with the previous reports and the human data in terms of syntenic homology between mouse and human chromosomes.

Mapping of the mouse Rxr loci encoding nuclear retinoid X receptors RXRα, RXRβ, and RXRγ

Recently, a novel subgroup of nuclear hormone receptors called RXRs implicated for retinoid-mediated gene regulation have been identified. RXRs appear to interact with many other nuclear hormone receptors and modulate their functions. We have mapped genetic loci Rxra, Rxrb, and Rxrg encoding three RXR subtypes, RXR alpha, RXR beta, and RXR gamma, respectively, using interspecific backcross mice. None of the Rxr loci cosegregated with each other or with the retinoic acid receptor loci (Rar) mapped previously. Rxra mapped to Chr 2 near the centromere, Rxrb mapped to the H-2 region of Chr 17, and Rxrg was tightly linked to the Pbx gene on distal Chr 1. These results underscore that RXR genes are dispersed in the genome.