Insertional mutation of the hairless locus on mouse chromosome 14

Le gènehairlessde la souris

The hairless gene in mammals encodes a nuclear factor that is highly expressed in skin and appears to control hair follicle integrity and cycling. In the absence of a normal and functional Hairless (Hr) protein, the hair bulb undergoes premature apoptosis during the first catagen stage of the hair cycle. The most striking effects of the mutation are loss of hair follicles and formation of epidermal utricles and dermal cysts. The hairless gene expression appears to be widespread and temporally regulated. The gene is strongly expressed in different compartments of the brain. Hairless mRNAs were detected in cartilage, gonads, thymus and colon. In addition to alopecia, hairless mice strains show subtle defects in the development and differentiation of various tissues and organs. The Hr protein is localised in cell nuclei and functions as a transcriptional regulator. Although its role has not been resolved in molecular terms, it was demonstrated that Hr is able to interact with multiple nuclear hormone receptors. Hr seems to be a part of a large multiprotein complex capable to repress transcription by its association to chromatin remodelling factors such as histone deacetylases. Recent experimental data suggest that Hr might be involved in Hox gene regulation, cell adhesion modulation and progenitor cells identity. At least in the skin, but probably in other organs, the Hr repressor seems to be responsible for the timing of epithelial cells differentiation.

A novel missense mutation in the mouse hairless gene causes irreversible hair loss: genetic and molecular analyses of Hr m1Enu

A novel autosomal recessive mutant was produced using N-ethyl-N-nitrosourea mutagenesis. The characteristics of the mutant mice included progressive irreversible hair loss within a month of birth, wrinkled skin, and long curved nails. Linkage analysis revealed that the causative gene is linked to D14Mit193 on chromosome 14. Sequence analysis of the complete cDNA of the candidate gene, hairless (Hr), identified a homozygous G-to-T transition at nucleotide 3572, leading to the substitution of glycine by tryptophan, designated Gly960Trp. This missense mutation occurs in the vicinity of repression domain 3 of the hairless protein (HR). This allele was named Hr(m1Enu). The relative amounts of Hr mRNA and HR protein determined by real-time PCR and Western blot analyses, respectively, were slightly elevated in the mutant mice. Quantitative real-time PCR analysis revealed the increased expression of Kc1 and Vdr in the mutant mice, whereas the expression of Nrs1 and Krtap16-6 was decreased. These results suggest that the Gly960Trp substitution in HR protein in Hr(m1Enu) mice may alter the function of HR as a transcriptional corepressor.

What is the 'true' function of skin?

Conventional textbook wisdom portrays the skin as an organ that literally enwraps whatever each of us stands for as a more or less functional, individual member of the mammalian species, and has it that the skin primarily establishes, controls and transmits contacts with the external world. In addition, the skin has long been recognized to protect the organism from deleterious environmental impacts (physical, chemical,microbiological), and is well-known as crucial for the maintenance of temperature, electrolyte and fluid balance. Now, ever more studies are being published that show the skin to also operate as a huge and highly active biofactory for the synthesis,processing and/or metabolism of an astounding range of e.g. structural proteins, glycans, lipids and signaling molecules. Increasingly, it becomes appreciated that the skin, furthermore, is an integral component of the immune, nervous and endocrine systems, with numerous lines of cross-talk between these systems established intracutaneously (e.g. Ann NY Acad Sci Vol 885, 1999; Endocrine Rev 21:457-487, 2000; Physiol Rev 80:980-1020, 2001; Exp Dermatol 10: 349-367, 2001). All these emerging cutaneous functions beyond the classical image of the skin as a barrier and sensory organ are immediately relevant for many of the quandaries that clinical dermatology, dermatopathology, and dermatopharmacology are still struggling with to-date, and offer the practising dermatologist attractive new targets for therapeutic intervention. Yet, many of these skin functions are not even mentioned in dermatology textbooks and await systematic therapeutic targeting. Following a suggestion by Enno Christophers, the current 'Controversies' feature brings together an unusually diverse council of biologists and clinicians, who share their thought-provoking views with the readers and allow us to peek into the future of research in cutaneous biology, not the least by reminding us of the -- often ignored -- evolutionary and embryonal origins of our favorite organ. Hopefully, this unique discussion feature will foster an understanding of the 'true' skin functions that is both more comprehensive and more profound than conventional teaching on this topic, and will stimulate more than 'skin-deep' reflections on the full range of skin functions.

Mutant laboratory mice with abnormalities in hair follicle morphogenesis, cycling, and/or structure: annotated tables

Numerous transgenic, targeted mutagenesis (so-called knockouts), conditional (so-called "gene switch") and spontaneous mutant mice develop abnormal hair phenotypes. The number of mice that exhibit such abnormalities is increasing exponentially as genetic engineering methods become routine. Since defined abnormalities in hair follicle morphogenesis, cycling and/or structure in such mutant mice provide important clues to the as yet poorly understood functional roles of many gene products, it is useful to summarize and classify these mutant mice according to their hair phenotype. This review provides a corresponding, annotated table of mutant mice with hair abnormalities, classifying the latter into 6 categories, 1) abnormally low number of hair follicles, 2) disorders of hair morphogenesis, 3) of hair follicle cycling, 4) of hair follicle structure 5) of sebaceous gland structure, and 6) hair growth disorders as a consequence of immunological abnormalities. This annotated table should serve as a useful source of reference for anyone who is interested in the molecular controls of hair growth, for investigators who are looking for mouse models to explore or compare the functional activities of their gene of interest, and for comparing the hair phenotype of newly generated mouse mutants with existing ones.

The hairless gene of the mouse: relationship of phenotypic effects with expression profile and genotype

Various mutations of the hairless (hr) gene of mice result in hair loss and other integument defects. To examine the role of the hr gene in mouse development, the expression profile of hr has been determined by in situ hybridisation and correlated to the nature of genetic changes and morphological abnormalities in different mutant animals. Four variant alleles have been characterised at the molecular level. hr/hr mice produce reduced, but significant, levels of hr mRNA whereas other alleles contain mutations which would be expected to preclude the synthesis of functional product, demonstrating a correlation between allelic variation at the hr locus and phenotypic severity. hr expression was shown to be widespread and temporally regulated. It was identified in novel tissues such as cartilage, developing tooth, inner ear, retina, and colon as well as in skin and brain. Analysis of mice homozygous for the rhino allele of hairless revealed that, although no morphological defects were detectable in many tissues normally expressing hr, previously undescribed abnormalities were present in several tissues including inner ear, retina, and colon. These findings indicate that the hairless gene product plays a wider role in development than previously suspected. Dev Dyn 1999;216:113-126.

The gene for hypotrichosis of Marie Unna maps between D8S258 and D8S298: exclusion of the hr gene by cDNA and genomic sequencing

Hypotrichosis of Marie Unna (MU) is an autosomal dominant hair-loss disorder with onset in childhood. A genomewide search for the gene was performed in a large Dutch family using 400 fluorescent microsatellite markers. Linkage was detected with marker D8S258, and analysis of this family and a further British kindred with additional markers in the region gave a combined maximum two-point LOD score of 13.42, with D8S560. Informative recombinants placed the MU gene in a 2.4-cM interval between markers D8S258 and D8S298. Recently, recessive mutations in the hr gene were reported in families with congenital atrichia, and this gene was previously mapped close to the MU interval. By radiation-hybrid mapping, we placed the hr gene close to D8S298 but were unable to exclude it from the MU interval. This, with the existence of the semidominant murine hr allele, prompted us to perform mutation analysis for this gene. Full-length sequencing of hr cDNA obtained from an affected individual showed no mutations. Similarly, screening of all exons of the hr gene amplified from the genomic DNA of an affected individual revealed no mutations. Analysis of expressed sequences and positional cloning of the MU locus is underway.

Molecular basis for the rhino Yurlovo (hr(rhY)) phenotype: severe skin abnormalities and female reproductive defects associated with an insertion in the hairless gene

In 1989, mice bearing mutations at the hr (hairless) locus were first proposed as a model for the human hair growth disorder papular atrichia, since in both these mice and in corresponding patients, a complete hair loss develops due to disintegration of the normal follicle structure into dermal cysts and so-called utriculi. Recently, the human hairless gene was characterized, and pathogenetic mutations were found to be associated with a recessively inherited form atrichia with papular lesions; however, the functions of hr gene remain unclear. Allelic mutations in the murine hairless gene represent a potentially powerful tool to elucidate the role of the hairless gene protein product in hair follicle physiology. In 1980, several naked animals were discovered in a breeding colony of B10.R109/Y mice maintained in the Laboratory of Experimental Biological Models (L.E.B.M., Yurlovo, Moscow District, Russia). By cross breeding with hairless HRS/J hr/hr mice, this mutation was shown to be allelic with hairless. Here, we describe the molecular basis of the hr(rhY) mutation in mice, which consists of a 13 bp insertion in exon 16 of the hr gene. Histological evaluation of Yurlovo mouse skin revealed some differences as compared to the hairless and rhino mutations, with the formation of dermal megacysts being the most specific peculiarity of the Yurlovo mutation. These results, together with previous studies of hr(rhY)/hr(rhY) mutant mice, suggest that the rhino Yurlovo (hr(rhY)) mutation represents a third and potentially more severe variation of the hairless phenotype.

Molecular and functional aspects of the hairless (hr) gene in laboratory rodents and humans

For many years, hairless and rhino mouse mutants have provided a useful and extensively exploited model for studying different aspects of skin physiology, including skin aging, pharmacokinetic evaluation of drug activity and cutaneous absorption, skin carcinogenesis, and skin toxicology. Interestingly, however, hairless and rhino mice have rarely been studied for their primary cellular defect - hairlessness - and thus, the hairless gene itself and its physiological functions have been largely overlooked for decades. The recent identification of the human homolog of the hairless gene on human Chromosome 8p12 confirmed the clinical significance of the phenomenon of "hairlessness" in humans, which was predicted on the basis of similarities between hairless mice and a congenital hair disorder characterized by atrichia with papules. Mutations in the hairless gene of mice provide instructive models for further studies of hr gene function, and may facilitate insights into the pathophysiology of different human disorders associated with the disruption of hr gene activity. We provide an overview of current data on the structure and expression patterns of the hr gene, and of mutations at the hairless locus in mice and humans, including the genetic basis of different alleles, the pathology of hairlessness, reproductive and immunological defects, and susceptibility to dioxin toxicity. On the basis of our current understanding of hairlessness, we speculate on the putative functions of the hr gene product in skin physiology, and particularly, in hair follicle biology.

Isolation and characterization of mouse minisatellites

Minisatellites provide the most informative system for analyzing processes of tandem repeat turnover in humans. However, little is known about minisatellites and the mechanisms by which they mutate in other species. To this end, we have isolated and characterized 76 endogenous mouse VNTRs. Fifty-one loci have been localized on mouse chromosomes and, unlike in humans, show no clustering in proterminal regions. Sequence analysis of 25 loci revealed the majority to be authentic minisatellites with GC-rich repeat units ranging from 14 to 47 bp in length. We have further characterized 3 of the most polymorphic loci both in Mus musculus subspecies and in inbred strains by using minisatellite variant repeat mapping (MVR) by PCR to gain insight into allelic diversity and turnover processes. MVR data suggest that mouse minisatellites mutate mainly by intra-allelic nonpolar events at a rate well below 10(-3) per gamete, in contrast to the high-frequency complex meiotic gene conversion-like events seen in humans. These results may indicate a fundamental difference in mechanisms of minisatellite mutation and genome turnover between mice and humans.

Physical characterization of the chromosomal rearrangements that accompany the transgene insertion in the chakragati mouse mutant

The circling phenotype of the chakragati mouse is a result of a transgenic insertional mutation. The absence of the phenotype in mice heterozygous for the transgene insertion suggests that this is due to a loss of function of an endogenous gene. Efforts to identify this gene have led to a previous report that sequences flanking the transgene, D16Ros1 and D16Ros2, map 10 cM apart in wildtype mice. We present here physical mapping data indicating that the proximity of D16Ros1 and D16Ros2 in the ckr mouse is explained by a duplication of D16Ros2 and its insertion along with the transgene at D16Ros1. We further demonstrate that D16Ros1 sequences are also duplicated and that this duplication is also part of the insertion at the endogenous D16Ros1 locus.

Activation of polyamine catabolism profoundly alters tissue polyamine pools and affects hair growth and female fertility in transgenic mice overexpressing spermidine/spermine N1-acetyltransferase

We have generated a transgenic mouse line that overexpresses the rate-controlling enzyme of polyamine catabolism, spermidine/spermine N1-acetyltransferase. Tissues of these mice showed markedly distorted polyamine pools, which in most cases were characterized by the appearance of N1-acetylspermidine, not normally found in mouse tissues, a massive accumulation of putrescine, and decreases in spermidine and/or spermine pools. The most striking phenotypic change was permanent hair loss at the age of 3 to 4 weeks which was typified histologically by the appearance of extensive follicular cysts in the dermis. The effect seemed attributable to putrescine interference with hair development, possibly with differentiation/proliferation of epidermal cells located in hair follicles. Female members of the transgenic line were found to be infertile apparently due to ovarian hypofunction and hypoplastic uteri. The findings demonstrate the utility of spermidine/spermine N1-acetyltransferase overexpression as an effective means for genetically modulating total tissue polyamine pools in transgenic animals and examining the developmental and oncogenic consequences.