Targeted expression of SV40 T antigen in the hair follicle of transgenic mice produces an aberrant hair phenotype

Characterization of the Promoter Regions of Two Sheep Keratin-Associated Protein Genes for Hair Cortex-Specific Expression

The keratin-associated proteins (KAPs) are the structural proteins of hair fibers and are thought to play an important role in determining the physical properties of hair fibers. These proteins are activated in a striking sequential and spatial pattern in the keratinocytes of hair fibers. Thus, it is important to elucidate the mechanism that underlies the specific transcriptional activity of these genes. In this study, sheep KRTAP 3–3 and KRTAP11-1 genes were found to be highly expressed in wool follicles in a tissue-specific manner. Subsequently, the promoter regions of the two genes that contained the 5′ flanking/5′ untranslated regions and the coding regions were cloned. Using an in vivo transgenic approach, we found that the promoter regions from the two genes exhibited transcriptional activity in hair fibers. A much stronger and more uniformly expressed green fluorescent signal was observed in the KRTAP11-1-ZsGreen1 transgenic mice. In situ hybridization revealed the symmetrical expression of sheep KRTAP11-1 in the entire wool cortex. Consistently, immunohistochemical analysis demonstrated that the pattern of ZsGreen1 expression in the hair cortex of transgenic mice matches that of the endogenous KRTAP11-1 gene, indicating that the cloned promoter region contains elements that are sufficient to govern the wool cortex-specific transcription of KRTAP11-1. Furthermore, regulatory regions in the 5′ upstream sequence of the sheep KRTAP11-1 gene that may regulate the observed hair keratinocyte specificity were identified using in vivo reporter assays.

Krtap16, characterization of a new hair keratin-associated protein (KAP) gene complex on mouse chromosome 16 and evidence for regulation by Hoxc13

Intermediate filament (IF) keratins and keratin-associated proteins (KAPs) are principal structural components of hair and encoded by members of multiple gene families. The severe hair growth defects observed upon aberrant expression of certain keratin and KAP genes in both mouse and man suggest that proper hair growth requires their spatio-temporally coordinated activation. An essential prerequisite for studying these cis-regulatory mechanisms is to define corresponding gene families, their genomic organization, and expression patterns. This work characterizes eight recently identified high glycine/tyrosine (HGT)-type KAP genes collectively designated Krtap16-n. These genes are shown to be integrated into a larger KAP gene domain on mouse chromosome 16 (MMU16) that is orthologous to a recently described HGT- and high sulfur (HS)-type KAP gene complex on human chromosome 21q22.11. All Krtap16 genes exhibit strong expression in a narrowly defined pattern restricted to the lower and middle cortical region of the hair shaft in both developing and cycling hair. During hair follicle regression (catagen), expression levels decrease until expression is no longer detectable in follicles at resting stage (telogen). Since isolation of the Krtap16 genes was based on their differential expression in transgenic mice overexpressing the Hoxc13 transcriptional regulator in hair, we examined whether bona fide Hoxc13 binding sites associated with these genes might be functionally relevant by performing electrophoretic mobility shift assays (EMSAs). The data provide evidence for sequence-specific interaction between Hoxc13 and Krtap16 genes, thus supporting the concept of a regulatory relationship between Hoxc13 and these KAP genes.

Directed differentiation of pluripotent cells to neural lineages: homogeneous formation and differentiation of a neurectoderm population

During embryogenesis the central and peripheral nervous systems arise from a neural precursor population, neurectoderm, formed during gastrulation. We demonstrate the differentiation of mouse embryonic stem cells to neurectoderm in culture, in a manner which recapitulates embryogenesis, with the sequential and homogeneous formation of primitive ectoderm, neural plate and neural tube. Formation of neurectoderm occurs in the absence of extraembryonic endoderm or mesoderm and results in a stratified epithelium of cells with morphology, gene expression and differentiation potential consistent with positionally unspecified neural tube. Differentiation of this population to homogeneous populations of neural crest or glia was also achieved. Neurectoderm formation in culture allows elucidation of signals involved in neural specification and generation of implantable cell populations for therapeutic use.

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.

Aneuploidy vs. gene mutation hypothesis of cancer: Recent study claims mutation but is found to support aneuploidy

For nearly a century, cancer has been blamed on somatic mutation. But it is still unclear whether this mutation is aneuploidy, an abnormal balance of chromosomes, or gene mutation. Despite enormous efforts, the currently popular gene mutation hypothesis has failed to identify cancer-specific mutations with transforming function and cannot explain why cancer occurs only many months to decades after mutation by carcinogens and why solid cancers are aneuploid, although conventional mutation does not depend on karyotype alteration. A recent high-profile publication now claims to have solved these discrepancies with a set of three synthetic mutant genes that "suffices to convert normal human cells into tumorigenic cells." However, we show here that even this study failed to explain why it took more than "60 population doublings" from the introduction of the first of these genes, a derivative of the tumor antigen of simian virus 40 tumor virus, to generate tumor cells, why the tumor cells were clonal although gene transfer was polyclonal, and above all, why the tumor cells were aneuploid. If aneuploidy is assumed to be the somatic mutation that causes cancer, all these results can be explained. The aneuploidy hypothesis predicts the long latent periods and the clonality on the basis of the following two-stage mechanism: stage one, a carcinogen (or mutant gene) generates aneuploidy; stage two, aneuploidy destabilizes the karyotype and thus initiates an autocatalytic karyotype evolution generating preneoplastic and eventually neoplastic karyotypes. Because the odds are very low that an abnormal karyotype will surpass the viability of a normal diploid cell, the evolution of a neoplastic cell species is slow and thus clonal, which is comparable to conventional evolution of new species.

Regulation of a hair follicle keratin intermediate filament gene promoter

During hair growth, cortical cells emerging from the proliferative follicle bulb rapidly undergo a differentiation program and synthesise large amounts of hair keratin proteins. To identify some of the controls that specify expression of hair genes we have defined the minimal promoter of the wool keratin intermediate filament gene K2.10. The region of this gene spanning nucleotides −350 to +53 was sufficient to direct expression of the lacZ gene to the follicle cortex of transgenic mice but deletion of nucleotides −350 to −150 led to a complete loss of promoter activity. When a four base substitution mutation was introduced into the minimal functional promoter at the binding site for lymphoid enhancer factor 1 (LEF-1), promoter activity in transgenic mice was decreased but specificity was not affected. To investigate the interaction of trans-acting factors within the minimal K2.10 promoter we performed DNase I footprinting analyses and electrophoretic mobility shift assays. In addition to LEF-1, Sp1, AP2-like and NF1-like proteins bound to the promoter. The Sp1 and AP2-like proteins bound sequences flanking the LEF-1 binding site whereas the NF1-like proteins bound closer to the transcription start site. We conclude that the LEF-1 binding site is an enhancer element of the K2.10 promoter in the hair follicle cortex and that factors other than LEF-1 regulate promoter tissue- and differentiation-specificity.

Sequences and differential expression of three novel human type-II hair keratins

As part of a program designed to characterize human hair keratin genes and their expression, we present the cDNA sequences and deduced amino acid sequences of three type-II hair keratins hHb3, hHb5, and hHb6, which by virtue of their amino acid homologies are the orthologs of the previously described sheep wool keratins, K2.10, K2.12, and K.211 [29]. Amino acid sequences comparisons of these keratins, including the previously characterized human K2.9 ortholog hHb1, show extreme conservation not only in the alpha-helices but also in the aminoterminal and proximal carboxyterminal domains. They also demonstrate higher sequence relationships between hHb1, hHb3, and hHb6 as compared to hHb5, which exhibits chain-specific sequences in both the head and tail domains. In situ hybridization studies using specific 3'-probes for the four type-II hair keratins reveal sequential patterns of gene expression in human anagen follicles. Remarkably the onset of hHb5 mRNA synthesis occurs immediately above a small population of matrix cells at the base of the hair bulb and the trichocytes lining the dermal papilla. hHb5 mRNA synthesis extends upward through the matrix and ends in the lower part of the cortex of the hair shaft. In contrast, both hHb1 and hHb3 mRNA synthesis begins simultaneously in the cortex 10-15 cell layers above the apex of the dermal papilla, thus partially overlapping that of hHb5 but continuing to a point well beyond hHb5 in the upper cortex. Synthesis of hHb6 mRNA starts slightly higher than either hHb1 or hHb3 mRNA and proceeds much farther up into the keratogenous zone of the hair shaft. Our study demonstrates that the differentiation of human hair in terms of hair keratin expression begins much earlier than previously assumed, i.e. in lower matrix cells of the hair bulb. This early phase of hair differentiation is followed by a late cortical phase of terminal differentiation which comprises at least three type-II hair keratins in the zone of elongation and the keratogenous zone of the hair shaft.

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.