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

Genetic insights into fiber quality, coat color and adaptation in Changthangi and Muzzafarnagri sheep: A comparative skin transcriptome analysis

Changthangi sheep, which inhabit the high-altitude regions of Ladakh, are known for their fine fiber production and are characterized by grey skin and either black or white coats. In contrast, Muzzafarnagri sheep from the plains of Uttar Pradesh produce coarse wool and have white skin and coats. We conducted comparative global gene expression profiling on four biological replicates of skin from each breed. Notably, our analysis identified 149 up-regulated genes and 2,139 down-regulated genes in Changthangi sheep compared to Muzzafarnagri sheep, with a p-adjusted value (padj) of ≤0.05 and a Log2 fold change of ≥1.5. Gene Ontology analysis of the up-regulated genes revealed an enrichment of terms related to melanin biosynthesis and developmental pigmentation. Additionally, enriched KEGG pathways included tyrosine metabolism and metabolic pathways. Among the melanogenesis-related genes that exhibited higher expression in Changthangi sheep were TYR, TYRP1, DCT, SLC45A2, PMEL, MLANA, and OCA2. These findings confirm melanin's role in both the animals' black coat color and UV protection at high-altitude. Furthermore, we observed more pronounced expression of genes related to fiber quality, namely KRTAP6, KRTAP7, KRTAP13, and KRTAP2, in the fine wool-producing sheep from Ladakh. The results of the RNA sequencing were validated using real-time PCR on 10 genes governing fiber quality and coat color, with ACTB and PPIB serving as reference genes. In conclusion, our comparative skin transcriptome analysis of Changthangi and Muzzafarnagri sheep sheds light on the genetic differences associated with distinct phenotypic traits and environmental adaptability, offering valuable insights into the underlying mechanisms.

miR-129-5p Participates in Hair Follicle Growth by Targeting HOXC13 in Rabbit

Mammalian hair formation is critically determined by the growth of hair follicles (HF). MiRNAs are crucial in the periodic development of hair follicles; they maintain epidermal homeostasis by targeting genes and influencing the activity of signaling pathways and related regulators. Our study discovered miR-129-5p to be overexpressed in the skin of Angora rabbits during catagen, and was negatively correlated with HOXC13 expression (Pearson’s R = −0.313, p < 0.05). The dual-Luciferase reporter gene detection system and Western blotting confirmed that miR-129-5p targeted HOXC13. In addition, miR-129-5p overexpression was found to significantly inhibit the expression of hair follicle development-related genes (HFDRGs), such as BCL2, WNT2, CCND1, and LEF1 (p < 0.01), and promoted the expression of SFRP2, TGF-β1, and FGF2 (p < 0.01), which was the same as the knockdown of HOXC13. In contrast, the knockout of miR-129-5p was the opposite, and it demonstrated similar results to the overexpression of HOXC13. CCK8 and flow cytometry demonstrated that miR-129-5p mimics significantly promoted the apoptosis of dermal papilla cells (DPCs) and inhibited proliferation (p < 0.01), while the inhibitor was found to reduce the apoptosis of DPCs and promote proliferation (p < 0.01). These results showed that miR-129-5p can participate in the periodic development of HF by targeting HOXC13, and it can induce apoptosis and inhibit proliferation of DPCs. These results will help to understand the role and mechanism of miR-129-5p in the periodic development of HF, and will provide support for subsequent studies, not only providing a theoretical basis for genetically improving the quality of hair in animals in the future, but also a new theory and method for diagnosing and treating hair loss in humans.

Identification of Key Pathways and Genes Related to the Development of Hair Follicle Cycle in Cashmere Goats

The development of hair follicle in cashmere goats shows significant periodic change, as with mice and humans. However, for cashmere goat with double-coat, the periodic change may be due to other regulatory molecules and signal pathways. To understand the mechanism of periodic development of hair follicle, we performed a weighted gene coexpression network analysis (WGCNA) to mine key genes and establish an interaction network by utilizing the NCBI public dataset. Ten coexpression modules, including 7689 protein-coding genes, were constructed by WGCNA, six of which are considered to be significantly related to the development of the hair follicle cycle. A functional enrichment analysis for each model showed that they are closely related to ECM- receptor interaction, focal adhesion, PI3K-Akt signaling pathway, estrogen signaling pathway, and so on. Combined with the analysis of differential expressed genes, 12 hub genes from coexpression modules were selected as candidate markers, i.e., COL1A1, C1QTNF6, COL1A2, AQP3, KRTAP3-1, KRTAP11-1, FA2H, NDUFS5, DERL2, MRPL14, ANTKMT and XAB2, which might be applied to improve cashmere production.

Characterization and functional analysis of Krtap11-1 during hair follicle development in Angora rabbits (Oryctolagus cuniculus)

BACKGROUND

Keratin-associated protein (KAP), the structural protein molecule of hair fibers, plays a key role in determining the physical properties of hair. Studies of Krtap11-1 have focused only on its localization. Functional studies of Krtap11-1 in hair follicle development have so far not been reported.

OBJECTIVE

This study aimed to provide evidence for the role of Krtap11-1 in skin and hair development.

METHODS

Full-length cloning and analysis of Krtap11-1 were conducted to ascertain its function. Overexpression vectors and interference sequences were constructed and transfected into RAB-9 cells. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to investigate the hair follicle developmental stage of Krtap11-1, the expression of different tissues, and the effects on other hair follicle development-related genes.

RESULTS

The full length of cloned Krtap11-1 was 947 bp. Krtap11-1 was confirmed to be a hydrophilic protein localized mostly in mitochondria. The greatest mRNA expression was observed in skin. Using a follicle synchronization model, it was found that Krtap11-1 mRNA expression levels first increased then decreased over the passage of time, principally during hair follicle catagen and telogen. Following the overexpression of Krtap11-1, mRNA expression levels of the WNT-2, KRT17, BMP-2, and TGF-β-1 genes increased, and LEF-1 decreased (P < 0.05), the converse after the corresponding use of si-RNA interference.

CONCLUSIONS

Krtap11-1 exerts a promoting effect. The results provide novel insight into the relationship between hair follicle development and Krtap11-1 gene expression.

Skin transcriptome reveals the periodic changes in genes underlying cashmere (ground hair) follicle transition in cashmere goats

Background

Cashmere goats make an outstanding contribution to the livestock textile industry and their cashmere is famous for its slenderness and softness and has been extensively studied. However, there are few reports on the molecular regulatory mechanisms of the secondary hair follicle growth cycle in cashmere goats. In order to explore the regular transition through the follicle cycle and the role of key genes in this cycle, we used a transcriptome sequencing technique to sequence the skin of Inner Mongolian cashmere goats during different months. We analyzed the variation and difference in genes throughout the whole hair follicle cycle. We then verified the regulatory mechanism of the cashmere goat secondary hair follicle growth cycle using fluorescence quantitative PCR.

Results

The growth cycle of cashmere hair could be divided into three distinct periods: a growth period (March–September), a regression period (September–December), and a resting period (December–March). The results of differential gene analyses showed that March was the most significant month. Cluster analysis of gene expression throughout the whole growth cycle further supported the key nodes of the three periods of cashmere growth, and the differential gene expression of keratin corresponding to the ground haircashmere growth cycle further supported the results from tissue slices. Quantitative fluorescence analysis showed that KAP3–1, KRTAP 8–1, and KRTAP 24–1 genes had close positive correlation with the cashmere growth cycle, and their regulation was consistent with the growth cycle of cashmere.

Conclusion

The growth cycle of cashmere cashmere could be divided into three distinct periods: a growth period (March–September), a regression period (September–December) and a resting period (December–March). March was considered to be the beginning of the cycle. KAP and KRTAP showed close positive correlation with the growth cycle of secondary hair follicle cashmere growth, and their regulation was consistent with the cashmere growth cycle. But hair follicle development-related genes are expressed earlier than cashmere growth, indicating that cycle regulation could alter the temporal growth of cashmere. This study laid a theoretical foundation for the study of the cashmere development cycle and provided evidence for key genes during transition through the cashmere cycle. Our study provides a theoretical basis for cashmere goat breeding.

Variation in the caprine keratin-associated protein 15-1 (KAP15-1) gene affects cashmere fibre diameter

Keratin-associated proteins (KAPs) are a structural component of cashmere fibre, and variation in some KAP genes (KRTAPs) has been associated with a number of caprine fibre traits. In this study, we report the identification of KRTAP15-1 in goats. Sequence variation in the gene was detected using the polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP) technique in 250 Longdong goats, and six variants (named A to F) containing eight single nucleotide polymorphisms (SNPs) were identified. Five of the SNPs were non-synonymous and would lead to putative amino acid changes. Reverse-transcription polymerase chain reaction (RT-PCR) analysis revealed that KRTAP15-1 was expressed in secondary hair follicles but not in heart tissue, liver tissue, lung tissue, kidney tissue or the longissimus dorsi muscle. Despite being rich in cysteine, the caprine KAP15-1 protein possesses a high content of serine and moderate content of glycine and phenylalanine. Association analyses revealed that KRTAP15-1 variant A was associated with decreased mean fibre diameter (MFD), and this effect appeared to be dominant; while variant C was found to be associated with increased MFD, the effect being recessive. The findings suggest that caprine KRTAP15-1 is highly polymorphic and that variation in this gene affects cashmere MFD.

The disrupted balance between hair follicles and sebaceous glands in Hoxc13-ablated rabbits

Pure hair and nail ectodermal dysplasia 9 (ECTD-9) is an autosomal recessive genetic disease caused by mutation of HOXC13 and is characterized by hypotrichosis and nail dystrophy in humans. Unlike patients with ECTD-9, Hoxc13-mutated mice and pigs do not faithfully recapitulate the phenotype of hypotrichosis, so there is a limited understanding of the molecular mechanism of Hoxc13-mediated hypotrichosis in animal models and clinically. Here, the homozygous Hoxc13^-/- rabbits showed complete loss of hair on the head and dorsum, whereas hypotrichosis in the limbs and tail were determined in the Hoxc13^-/- rabbits. In addition, reduced hair follicles (HFs) while the enlarged and increased number of sebaceous glands (SGs) were also found in the Hoxc13^-/- rabbits, showing that the disrupted balance between HFs and SGs may respond to hypotrichosis of ECTD-9 in an animal model and clinically. Therefore, our findings demonstrate that Hoxc13^-/- rabbits can be used as a model for human ECTD-9, especially to understand the pathologic mechanism of hypotrichosis. Moreover, the disrupted balance between HFs and SGs, especially in the Hoxc13^-/- rabbits, can be used as an ideal animal model for dermatology ailments, such as acne and hypotrichosis, in preclinical studies.-Deng, J., Chen, M., Liu, Z., Song, Y., Sui, T., Lai, L., Li, Z. The disrupted balance between hair follicles and sebaceous glands in Hoxc13-ablated rabbits.

HOXC13 and HSP27 Expression in Skin and the Periodic Growth of Secondary Fiber Follicles from Longdong Cashmere Goats Raised in Different Production Systems

This experiment was conducted to identify periodic changes in secondary follicles (SFs) over one year of extensive (grazed) and intensive (housed and fed supplement) farming of Longdong cashmere goats. One-year old goats (n = 24, 12 extensively fed and 12 intensively fed) were studied. The diameter, depth, density, activity, and ultra-structural features of SFs were assessed using light microscopy and transmission electron microscopy. HOXC13 and HSP27 expression were studied using immunohistochemistry and immunofluorescence method. The anagen stage in the extensively grazed goats was from April to September, but was longer (April to October) in the housed, supplementary fed group. The depth and activity of the SF in anagen and catagen differed (P < 0.05) between the groups. HSP27 and HOXC13 protein were present in both the epidermis and dermis, with HSP27 immunoreactivity highest in the hair shaft (HS), outer root sheath (ORS) and inner root sheath (IRS). HOXC13 expression was prominent in both the eprdermis and ORS. HSP27 and HOXC13 expression were prominent during anagen, and less so during catagen and telogen. In anagen, HSP27 expression in the HS, IRS, and ORS of the extensively fed group was higher than in the intensively fed group (p < 0.05). In contrast, HOXC13 expression in HS, IRS and ORS of the extensively fed group was lower than in the intensively fed group (P < 0.05). This suggests the growth of cashmere is influenced by nutrition and that housed goats could be used in cashmere production. Anat Rec, 301:742-752, 2018. © 2017 Wiley Periodicals, Inc.

Genetics of syndromic and non-syndromic hereditary nail disorders

The nail is a unique epithelial skin appendage made up of a fully keratinized nail plate. The nail can be affected in several systemic illnesses, dermatological diseases, and inherited nail disorders. Nail dystrophies can present as isolated disorders or as a part of syndromes. Substantial progress has been achieved in the management and diagnosis of nail diseases; however, not much is known about the underlying molecular controls of nail growth. The homeostasis and development of the nail appendage depend on the intricate interactions between the epidermis and underlying mesenchyme, and comprise different signaling pathways such as the WNT signaling pathway. Digit-tip regeneration in mice and humans has been a known fact for the past six decades; however, only recently the underlying biological mechanisms by which the nail organ achieves digit regeneration have been elucidated. Moreover, significant progress has been made in identifying nail stem cells and localizing stem cell niches in the nail unit. More fascinating, however, is the role they play in orchestrating the processes that lead to the regeneration of the digit. Further elucidating the role of nail stem cells and the signaling pathways driving epithelial-mesenchymal interactions in the nail unit might contribute to the development of novel therapeutic tools for amputees.

Hoxc13 is a crucial regulator of murine hair cycle

Hair follicles undergo cyclical growth and regression during postnatal life. Hair regression is an apoptosis-driven process strictly controlled by micro- and macro-environmental signals. However, how these signals are controlled remains largely unknown. Hoxc13, a member of the Hox gene family, is reported to play an important role in hair follicle differentiation. In the present study, we observed that Hoxc13 was highly expressed in the outer root sheath, matrix, medulla and inner root sheath of hair follicles in a hair cycle-dependent manner. We therefore investigated the role of Hoxc13 in hair follicle cycling. Injection of ShRNA (ShHoxc13) to suppress Hoxc13 in early anagen promoted premature catagen entry, shown by significantly decreased hair length and hair bulb size, increased percentage of catagen hair follicles, hair cycle score and TUNEL+ cells and inhibited proliferation. In contrast, local injection of recombinant Hoxc13 polypeptide (rhHoxc13) during the late anagen phase prolonged the anagen phase. Additionally, rhHoxc13 injections during the telogen phase significantly promoted hair growth and induced the anagen progression. At the molecular level, the expression of phosphorylated smad2 (p-smad2), a key factor of active TGF-β1 signaling, was up-regulated in the ShHoxc13-treated hair follicles and down-regulated in rhHoxc13-treated hair follicles, suggesting that Hoxc13 might block anagen-catagen transition by inhibiting the TGF-β1 signaling. Taken together, our data strongly suggest that Hoxc13 is a novel and crucial regulator of the hair cycle. This might also provide an understanding of the mechanism of the 'hair cycle clock' and the development of alopecia treatments.

Dysregulated expression of sterol O-acyltransferase 1 (Soat1) in the hair shaft of Hoxc13 null mice

The cholesterol-metabolizing enzyme sterol O-acetyltransferase (SOAT1) is implicated in an increasing number of biological and pathological processes in a number of organ systems, including the differentiation of the hair shaft. While the functional and regulatory mechanisms underlying these diverse functional roles remain poorly understood, the compartment of the hair shaft known as medulla, affected by mutations in Soat1, may serve as a suitable model for defining some of these mechanisms. A comparative analysis of mRNA and protein expression patterns of Soat1/SOAT1 and the transcriptional regulator Hoxc13/HOXC13 in postnatal skin of FVB/NTac mice indicated co-expression in the most proximal cells of the differentiating medulla. This finding combined with the significant downregulation of Soat1 expression in postnatal skin of both Hoxc13 gene-targeted and transgenic mice based on previously reported DNA microarray results suggests a potential regulatory relationship between the two genes. Non-detectable SOAT1 expression in the defective hair follicle medulla of Hoxc13(tm1Mrc) mice and evidence for binding of HOXC13 to the Soat1 upstream control region obtained by ChIP assay suggests that Soat1 is a downstream regulatory target for HOXC13 during medulla differentiation.

Determination of Secondary Follicle Characteristics, Density, Activity, and Hoxc13 Expression Pattern of Hexi Cashmere Goats Breed

This experiment was conducted to identify some aspects of secondary follicle (SF) characteristics of Hexi cashmere goats at five different growing stages in one year in order and discover the expression pattern of Hoxc13 in a SF cycling to provide morphological basis for studying the growth of cashmere. Ten cashmere goats of one-year old (5 males, 5 females) were included in this study. The density and activity of SF were observed and measured by making paraffin sections, the ultra-structural features of SF were studied under transmission electron microscopy (TEM) by making ultra-thin sections, and the expression of Hoxc13 was investigated through the immunohistochemistry method. The average diameter of SF had the smallest value in the anagen stage, and significant difference (P < 0.05) was found between the anagen stage and other stages. The density of SF increased gradually through the different growing stages, and significant difference was found between the anagen and procatagen stages (P < 0.05). With an increase in time (months), the percentage of SF activity increased, and significant difference in the percentage of SF activity was found between the telogen and anagen stages (P < 0.05). At the telogen stage, the layers of connective tissue sheath (CTS) of SF were unclear, hemidesmosomes between the outer root sheath (ORS) and basement membrane disappeared, and dead cells were found at the top of the SF. The rudiments of new SF were found in the proanagen stage, CTS was thickened, and the cells of ORS were stretched out like fingers. At the anagen stage, the structure of SF was integral, and the inner root sheath (IRS) consisted of three concentric layers (Helen, Huxley, and Cuticle layers). The cells of Huxley's layer degenerated gradually, and pseudopodia were formed on the cells of ORS in the procatagen stage. At the catagen stage, the ORS was separated from the IRS, and IRS disappeared. Huxley's layer was absent in the inactive SF while, the ORS was present in the active SF. Hoxc 13 was expressed in the epidermis and sebaceous gland o, ORS, IRS, hair shaft of SF in the skin. Hoxc13 was expressed weakly during procatagen, catagen, and telogen stage, while with an increase in proanagen and anagen stage, significant difference was found between them. These findings demonstrated the ultra-structural features of SF could provide the useful activity criteria, and Hoxc13 associated with the SF activity.

Crisp1 and alopecia areata in C3H/HeJ mice

Alopecia areata (AA), a cell mediated autoimmune disease, is the second most common form of hair loss in humans. While the autoimmune disease is responsible for the underlying pathogenesis, the alopecia phenotype is ultimately due to hair shaft fragility and breakage associated with structural deficits. Quantitative trait genetic analyses using the C3H/HeJ mouse AA model identified cysteine-rich secretory protein 1 (Crisp1), a hair shaft structural protein, as a candidate gene within the major AA locus. Crisp1 transcripts in the skin at various times during disease development were barely detectable. In situ hybridization identified Crisp1 expression within the medulla of hair shafts from clinically normal strains of mice but not C3H/HeJ mice with AA. Follow-up work with 5-day-old C3H/HeJ mice with normal hair also had essentially no expression of Crisp1. Other non-inflammatory based follicular dystrophy mouse models with similar hair shaft abnormalities also have little or no Crisp1 expression. Shotgun proteomics, used to determine strain difference in hair proteins, confirmed that there was very little CRISP1 within normal C3H/HeJ mouse hair in comparison to 11 other strains. However, mutant mice with hair medulla defects also had undetectable levels of CRISP1 in their hair. Crisp1 null mice had normal skin, hair follicles, and hair shafts indicating that the lack of the CRISP1 protein does not translate directly into defects in the hair shaft or hair follicle. These results suggest that CRISP1 may be an important structural component of mouse hair and that its strain-specific dysregulation may indicate a predisposition to hair shaft disease such as AA.

Mammalian keratin associated proteins (KRTAPs) subgenomes: disentangling hair diversity and adaptation to terrestrial and aquatic environments

Background

Adaptation of mammals to terrestrial life was facilitated by the unique vertebrate trait of body hair, which occurs in a range of morphological patterns. Keratin associated proteins (KRTAPs), the major structural hair shaft proteins, are largely responsible for hair variation.

Results

We exhaustively characterized the KRTAP gene family in 22 mammalian genomes, confirming the existence of 30 KRTAP subfamilies evolving at different rates with varying degrees of diversification and homogenization. Within the two major classes of KRTAPs, the high cysteine (HS) subfamily experienced strong concerted evolution, high rates of gene conversion/recombination and high GC content. In contrast, high glycine-tyrosine (HGT) KRTAPs showed evidence of positive selection and low rates of gene conversion/recombination. Species with more hair and of higher complexity tended to have more KRATP genes (gene expansion). The sloth, with long and coarse hair, had the most KRTAP genes (175 with 141 being intact). By contrast, the “hairless” dolphin had 35 KRTAPs and the highest pseudogenization rate (74% relative to the 19% mammalian average). Unique hair-related phenotypes, such as scales (armadillo) and spines (hedgehog), were correlated with changes in KRTAPs. Gene expression variation probably also influences hair diversification patterns, for example human have an identical KRTAP repertoire as apes, but much less hair.

Conclusions

We hypothesize that differences in KRTAP gene repertoire and gene expression, together with distinct rates of gene conversion/recombination, pseudogenization and positive selection, are likely responsible for micro and macro-phenotypic hair diversification among mammals in response to adaptations to ecological pressures.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-779) contains supplementary material, which is available to authorized users.

Expression analysis of KAP9.2 and Hoxc13 genes during different cashmere growth stages by qRT-PCR method

Keratin-associated protein 9.2 (KAP9.2) and Homeobox C13 (Hoxc13) genes were chosen to study because of their biological functions involving hair formation. KAP9.2 gene belongs to the ultra high sulfur KAPs, which is important for hair formation and may have association with cashmere. Hoxc13 takes part in the formation of cashmere keratin and maintaining the normal structure of follicle. It has been reported that Hoxc13 gene exists binding site of KP and KAP genes at its promoter regions in mouse. So the expression of KAP9.2 and Hoxc13 genes was detected at anagen stage vs telogen stage by qRT-PCR. The data showed that KAP9.2 and Hoxc13 gene had similar expression trend at different stages, which indicated that there was interaction between them. KAP9.2 and Hoxc13 gene had lower expression level in anagen than that of in telogen of cashmere growth. In anagen, KAP9.2 and Hoxc13 expressed lower in high cashmere yield individuals than that of in low cashmere yield ones. In telogen, the result was reverse. The study would provide the evidence of involvement of KAP9.2 and Hoxc13 in hair periodic growth.

Autosomal recessive transmission of a rare KRT74 variant causes hair and nail ectodermal dysplasia: allelism with dominant woolly hair/hypotrichosis

Pure hair and nail ectodermal dysplasia (PHNED) comprises a heterogeneous group of rare heritable disorders characterized by brittle hair, hypotrichosis, onychodystrophy and micronychia. Autosomal recessive (AR) PHNED has previously been associated with mutations in either KRT85 or HOXC13 on chromosome 12p11.1-q14.3. We investigated a consanguineous Pakistani family with AR PHNED linked to the keratin gene cluster on 12p11.1 but without detectable mutations in KRT85 and HOXC13. Whole exome sequencing of affected individuals revealed homozygosity for a rare c.821T>C variant (p.Phe274Ser) in the KRT74 gene that segregates AR PHNED in the family. The transition alters the highly conserved Phe274 residue in the coil 1B domain required for long-range dimerization of keratins, suggesting that the mutation compromises the stability of intermediate filaments. Immunohistochemical (IHC) analyses confirmed a strong keratin-74 expression in the nail matrix, the nail bed and the hyponychium of mouse distal digits, as well as in normal human hair follicles. Furthermore, hair follicles and epidermis of an affected family member stained negative for Keratin-74 suggesting a loss of function mechanism mediated by the Phe274Ser substitution. Our observations show for the first time that homozygosity for a KRT74 missense variant may be associated with AR PHNED. Heterozygous KRT74 mutations have previously been associated with autosomal dominant woolly hair/hypotrichosis simplex (ADWH). Thus, our findings expand the phenotypic spectrum associated with KRT74 mutations and imply that a subtype of AR PHNED is allelic with ADWH.

A forward phenotypically driven unbiased genetic analysis of host genes that moderate herpes simplex virus virulence and stromal keratitis in mice

Both viral and host genetics affect the outcome of herpes simplex virus type 1 (HSV-1) infection in humans and experimental models. Little is known about specific host gene variants and molecular networks that influence herpetic disease progression, severity, and episodic reactivation. To identify such host gene variants we have initiated a forward genetic analysis using the expanded family of BXD strains, all derived from crosses between C57BL/6J and DBA/2J strains of mice. One parent is highly resistant and one highly susceptible to HSV-1. Both strains have also been fully sequenced, greatly facilitating the search for genetic modifiers that contribute to differences in HSV-1 infection. We monitored diverse disease phenotypes following infection with HSV-1 strain 17syn+ including percent mortality (herpes simplex encephalitis, HSE), body weight loss, severity of herpetic stromal keratitis (HSK), spleen weight, serum neutralizing antibody titers, and viral titers in tear films in BXD strains. A significant quantitative trait locus (QTL) on chromosome (Chr) 16 was found to associate with both percent mortality and HSK severity. Importantly, this QTL maps close to a human QTL and the gene proposed to be associated with the frequency of recurrent herpetic labialis (cold sores). This suggests that a single host locus may influence these seemingly diverse HSV-1 pathogenic phenotypes by as yet unknown mechanisms. Additional suggestive QTLs for percent mortality were identified—one on Chr X that is epistatically associated with that on Chr 16. As would be anticipated the Chr 16 QTL also modulated weight loss, reaching significance in females. A second significant QTL for maximum weight loss in male and female mice was mapped to Chr 12. To our knowledge this is the first report of a host genetic locus that modulates the severity of both herpetic disease in the nervous system and herpetic stromal keratitis.

Krtap11-1, a hair keratin-associated protein, as a possible crucial element for the physical properties of hair shafts

BACKGROUND

The physical properties of the hair are predominantly determined by the assembly of keratin bundles. The keratin-associated proteins (Krtaps) are thought to be involved in keratin bundle assembly, however, the functional role of the individual member still remains largely unknown.

OBJECTIVE

The aim of this study is to clarify the role of a unique class of Krtaps, Krtap11-1, in the development and physical properties of the hair.

METHODS

The expression regulation of Krtap11-1 was analyzed and its binding partners in the hair cortex were determined. Also, the effects of the forcible expression of this protein on the hair follicle development were analyzed in culture.

RESULTS

The expression pattern of Krtap11-1 was concentrically asymmetric in the faulty hair that develops in Foxn1nu mice. In cultured keratinocytes, the expression of Krtap11-1 transgene product was strictly regulated by the keratinization process and proteasome-dependent protein elimination. While the association with keratin as well as the cohesive self-assembly of Krtap11-1 appeared to be stabilized by disulfide cross-links, the biotinylated Krtap11-1 probe enabled the adherence to certain type I keratins in the hair cortex, including K31, 33 and 34, in the absence of disulfide formation. When embryonic upper lip rudiments were forcibly introduced with Krtap11-1, the hair follicles formed irregularly arranged globular hair keratin-clumps surrounded by multilayered epithelial cells in culture.

CONCLUSION

Krtap11-1 may play an important role on keratin-bundle assembly in the hair cortex and this study provides insight into the physical properties of the hair shaft.

A homozygous frameshift mutation in the HOXC13 gene underlies pure hair and nail ectodermal dysplasia in a Syrian family

Pure hair and nail ectodermal dysplasia (PHNED) is a rare genetic disorder characterized by hypotrichosis or complete alopecia, as well as nail dystrophy. Mutations in the type II hair keratin gene KRT85 and the HOXC13 gene on chromosome 12q have recently been identified in families with autosomal-recessive PHNED. In the present study, we have analyzed a consanguineous Syrian family with an affected girl having complete alopecia and nail dystrophy since birth. The family clearly showed linkage to chromosome 12q13.13-12q14.3, which excluded the KRT85 gene. Sequencing of another candidate gene HOXC13 within the linkage interval identified a homozygous frameshift mutation (c.355delC; p.Leu119Trpfs*20). Expression studies in cultured cells revealed that the mutant HOXC13 protein mislocalized within the cytoplasm, and failed to upregulate the promoter activities of its target genes. Our results strongly suggest crucial roles of the HOXC13 gene in the development of hair and nails in humans.

Loss-of-function mutations in HOXC13 cause pure hair and nail ectodermal dysplasia

Pure hair and nail ectodermal dysplasia (PHNED) is a congenital condition characterized by hypotrichosis and nail dystrophy. Autosomal-recessive PHNED has previously been mapped to chromosomal region 12q12-q14.1, which contains the type II hair keratin and HOXC clusters. Hoxc13-null mice are known to develop hair and nail defects very similar to those seen in human PHNED. We performed whole-exome sequencing in a consanguineous Chinese family affected by PHNED and identified a homozygous nonsense mutation (c.390C>A [p.Tyr130(∗)]) in HOXC13 in all affected individuals. In an additional affected female from a consanguineous Afghan family, we found a 27.6 kb homozygous microdeletion involving the first exon of HOXC13. We examined HOXC13 expression in scalp specimen obtained from the index individual of the Chinese family and detected dramatically reduced mRNA levels in skin tissue and nearly absent protein staining in hair follicles, suggesting a mechanism of nonsense-mediated mRNA decay. We also observed markedly decreased expression of four HOXC13 target genes in the specimen. Taken together, our results demonstrate that loss-of-function mutations in HOXC13 cause autosomal-recessive PHNED and further highlight the importance of HOXC13 in hair and nail development.

Alopecia in a viable phospholipase C delta 1 and phospholipase C delta 3 double mutant

BACKGROUND

Inositol 1,4,5trisphosphate (IP(3)) and diacylglycerol (DAG) are important intracellular signalling molecules in various tissues. They are generated by the phospholipase C family of enzymes, of which phospholipase C delta (PLCD) forms one class. Studies with functional inactivation of Plcd isozyme encoding genes in mice have revealed that loss of both Plcd1 and Plcd3 causes early embryonic death. Inactivation of Plcd1 alone causes loss of hair (alopecia), whereas inactivation of Plcd3 alone has no apparent phenotypic effect. To investigate a possible synergy of Plcd1 and Plcd3 in postnatal mice, novel mutations of these genes compatible with life after birth need to be found.

METHODOLOGY/PRINCIPAL FINDINGS

We characterise a novel mouse mutant with a spontaneously arisen mutation in Plcd3 (Plcd3(mNab)) that resulted from the insertion of an intracisternal A particle (IAP) into intron 2 of the Plcd3 gene. This mutation leads to the predominant expression of a truncated PLCD3 protein lacking the N-terminal PH domain. C3H mice that carry one or two mutant Plcd3(mNab) alleles are phenotypically normal. However, the presence of one Plcd3(mNab) allele exacerbates the alopecia caused by the loss of functional Plcd1 in Del(9)olt1Pas mutant mice with respect to the number of hair follicles affected and the body region involved. Mice double homozygous for both the Del(9)olt1Pas and the Plcd3(mNab) mutations survive for several weeks and exhibit total alopecia associated with fragile hair shafts showing altered expression of some structural genes and shortened phases of proliferation in hair follicle matrix cells.

CONCLUSIONS/SIGNIFICANCE

The Plcd3(mNab) mutation is a novel hypomorphic mutation of Plcd3. Our investigations suggest that Plcd1 and Plcd3 have synergistic effects on the murine hair follicle in specific regions of the body surface.

Msx2 and Foxn1 regulate nail homeostasis

Epithelial-mesenchymal interactions underlie the foundation for ectodermal appendage formation. Signal molecules such as BMPs and WNTs mediate crosstalk between the two tissue layers and coordinate both the induction and morphogenesis of ectodermal appendages. Here, we analyzed the function of two BMP downstream transcription factors, Msx2 and Foxn1, in nail differentiation. First, we show that Msx2 function is required during onychocyte (nail cell) terminal differentiation. Second, the Msx2/Foxn1/hair keratin pathway controlling hair differentiation is also conserved during onychocyte differentiation. Finally, the Msx2-/-; Foxn1-/- double-mutant nails exhibit a more severe phenotype than either single mutant including nail bed hyperplasia. Together, our data implicate important functions for Msx2 and Foxn1 in regulating differentiation of the keratogenous zone, proliferation of distal nail matrix cells, and organization of the nail bed.

The nude mutant gene Foxn1 is a HOXC13 regulatory target during hair follicle and nail differentiation

Among the Hox genes, homeobox C13 (Hoxc13) has been shown to be essential for proper hair shaft differentiation, as Hoxc13 gene-targeted (Hoxc13(tm1Mrc)) mice completely lack external hair. Because of the remarkable overt phenotypic parallels to the Foxn1(nu) (nude) mutant mice, we sought to determine whether Hoxc13 and forkhead box N1 (Foxn1) might act in a common pathway of hair follicle (HF) differentiation. We show that the alopecia exhibited by both the Hoxc13(tm1Mrc) and Foxn1(nu) mice is because of strikingly similar defects in hair shaft differentiation and that both mutants suffer from a severe nail dystrophy. These phenotypic similarities are consistent with the extensive overlap between Hoxc13 and Foxn1 expression patterns in the HF and the nail matrix. Furthermore, DNA microarray analysis of skin from Hoxc13(tm1Mrc) mice identified Foxn1 as significantly downregulated along with numerous hair keratin genes. This Foxn1 downregulation apparently reflects the loss of direct transcriptional control by HOXC13 as indicated by our results obtained through co-transfection and chromatin immunoprecipitation (ChIP) assays. As presented in the discussion, these data support a regulatory model of keratinocyte differentiation in which HOXC13-dependent activation of Foxn1 is part of a regulatory cascade controlling the expression of terminal differentiation markers.

[Hoxc13 and the development of hair follicle]

Hoxc13 belongs to the Abd-B class of Hox gene family, which participated in the hair follicle formation and hair growth regulation process. The structural protein of hair KP (keratin) and KAP (keratin-associated protein) expression is under regulation of Hoxc13, and then changes the characteristics of hair by regulating the composition of these two types of hair proteins and maintaining the normal morphology of hair follicle. In this review, we summarized that the relationship between the expression level of Hoxc13 and hair follicle development/hair growth and the mechanisim under the controling of Hoxc13 and relevant genes.

Desmoglein 4 is regulated by transcription factors implicated in hair shaft differentiation

The hair fiber is made of specialized keratinocytes, known as trichocytes, that primarily express hair keratins, which are cemented by a multitude of keratin-associated proteins (KAPs). The hair keratins form the intermediate filament cytoskeleton of the trichocytes, which are linked to abundant cell-cell adhesion junctions, called desmosomes. Desmoglein 4 (DSG4) is the major desmosomal cadherin expressed in the hair shaft cortex where the hair keratins are highly expressed. In humans, mutations affecting either the hair keratins or DSG4 lead to beaded hair phenotypes with features of monilethrix. In this work, we postulated that the regulatory pathways governing the expression of hair shaft components, such as hair keratins and DSG4, are shared. Therefore, we studied the transcriptional regulation of DSG4 by transcription factors/pathways that are known regulators of hair keratin or KAP expression. We show that HOXC13, LEF1 and FOXN1 repress DSG4 transcription and provide in vitro and in vivo evidence correlating the Notch pathway with the activation and/or maintenance of DSG4 expression in the hair follicle.

Circadian clock genes contribute to the regulation of hair follicle cycling

Hair follicles undergo recurrent cycling of controlled growth (anagen), regression (catagen), and relative quiescence (telogen) with a defined periodicity. Taking a genomics approach to study gene expression during synchronized mouse hair follicle cycling, we discovered that, in addition to circadian fluctuation, CLOCK-regulated genes are also modulated in phase with the hair growth cycle. During telogen and early anagen, circadian clock genes are prominently expressed in the secondary hair germ, which contains precursor cells for the growing follicle. Analysis of Clock and Bmal1 mutant mice reveals a delay in anagen progression, and the secondary hair germ cells show decreased levels of phosphorylated Rb and lack mitotic cells, suggesting that circadian clock genes regulate anagen progression via their effect on the cell cycle. Consistent with a block at the G1 phase of the cell cycle, we show a significant upregulation of p21 in Bmal1 mutant skin. While circadian clock mechanisms have been implicated in a variety of diurnal biological processes, our findings indicate that circadian clock genes may be utilized to modulate the progression of non-diurnal cyclic processes.

Role of homeobox genes in the patterning, specification, and differentiation of ectodermal appendages in mammals

Homeobox genes are an evolutionarily conserved class of transcription factors that are key regulators during developmental processes such as regional specification, patterning, and differentiation. In this review, we summarize the expression pattern, loss- and/or gain-of-function mouse models, and naturally occurring mouse and human mutations of known homeobox genes required for the development of ectodermal appendages.

Identification of novel glucocorticoid receptor-regulated genes involved in epidermal homeostasis and hair follicle differentiation

Despite that glucocorticoids (GCs), acting through the glucocorticoid receptor (GR) exert a pivotal role in skin physiopathology, specific genes regulated by GR in this tissue are largely unknown. We have used a transgenic mouse model overexpressing GR in epidermal basal cells and outer root sheath (ORS) of the hair follicle (HF) under the control of the keratin 5 regulatory sequences (K5-GR mice) to identify GR-regulated genes in mouse skin. We analyzed the transcriptomic profile of adult K5-GR skin as compared to non-transgenic adult mice by using oligonucleotide microarrays and identified 173 genes differentially regulated by GR in this tissue. Our data were further validated by semiquantitative RT-PCR and quantitative real-time PCR. We have identified a large subset of hair keratin intermediate filament (krt) and hair keratin-associated protein (krtap) genes, as well as several hox genes as GC-regulated. Since dysregulation of krt, krtaps and hox genes can cause hair disorders, as it occurs in adult K5-GR mice, our findings strongly suggest a role of GR in HF morphogenesis through the coordinated regulation of these hair-specific genes. In addition, we found that GR repressed several genes related to cell growth, such as the immediate early genes fosb and c-fos, according to the antiproliferative role described for this hormone receptor. By using cultured keratinocytes treated with GR-agonists and -antagonists, we demonstrated that down-regulation of fosb is mediated by GR. Identification of novel GR-regulated genes will help us to better understand the role of GCs as physiological modulators and pharmacological agents.

Influence of TRPV3 mutation on hair growth cycle in mice

We recently reported that Gly573Ser substitution of the transient receptor potential cation channel, subfamily V member 3 (TRPV3) caused hair loss in DS-Nh mice. To further elucidate the effects of this mutation on the development of the spontaneous hairless phenotype, we examined the temperature-response to epidermal sheets from DS-Nh and DS mice. It was indicated that the mutation was gain-of-function. We also performed genetic and histological analyses with both strain skins. DNA microarray data revealed that the levels of keratin-associated protein 16-1, 16-3, and 16-9 genes related to the anagen phase were decreased in the skins of DS-Nh mice compared with those of three days old DS mice. Histological analysis revealed that the anagen phase persisted in DS-Nh mice, and that the telogen phase was seen in DS but not DS-Nh mice at 21 days of age. Regulation of TRPV3 appears to be important for appropriate hair development in rodents.

Lymphotoxin-beta regulates periderm differentiation during embryonic skin development

Lymphotoxin-beta (LTbeta) is a key regulator of immune system development, but also affects late stages in hair development. In addition, high expression of LTbeta at an early stage in epidermis hinted at a further function in hair follicle induction or epithelial development. We report that hair follicles were normally induced in LTbeta(-/-) skin, but the periderm detached from the epidermis earlier, accompanied by premature appearance of keratohyalin granules. Expression profiling revealed dramatic down-regulation of a gene cluster encoding periderm-specific keratin-associated protein 13 and four novel paralogs in LTbeta(-/-) skin prior to periderm detachment. Epidermal differentiation markers, including small proline-rich proteins, filaggrins and several keratins, were also affected, but transiently in LTbeta(-/-) skin at the time of abnormal periderm detachment. As expected, Tabby mice, which lack the EDA gene, the putative upstream regulator of LTbeta in skin, showed similar though milder periderm histopathology and alterations in gene expression. Overall, LTbeta shows a primary early function in periderm differentiation, with later transient effects on epidermal and hair follicle differentiation.

Evidence that the satin hair mutant gene Foxq1 is among multiple and functionally diverse regulatory targets for Hoxc13 during hair follicle differentiation

It is increasingly evident that the molecular mechanisms underlying hair follicle differentiation and cycling recapitulate principles of embryonic patterning and organ regeneration. Here we used Hoxc13-overexpressing transgenic mice (also known as GC13 mice), known to develop severe hair growth defects and alopecia, as a tool for defining pathways of hair follicle differentiation. Gene array analysis performed with RNA from postnatal skin revealed differential expression of distinct subsets of genes specific for cells of the three major hair shaft compartments (cuticle, cortex, and medulla) and their precursors. This finding correlates well with the structural defects observed in each of these compartments and implicates Hoxc13 in diverse pathways of hair follicle differentiation. The group of medulla-specific genes was particularly intriguing because this included the developmentally regulated transcription factor-encoding gene Foxq1 that is altered in the medulladefective satin mouse hair mutant. We provide evidence that Foxq1 is a downstream target for Hoxc13 based on DNA binding studies as well as co-transfection and chromatin immunoprecipitation assays. Expression of additional medulla-specific genes down-regulated upon overexpression of Hoxc13 requires functional Foxq1 as their expression is ablated in hair follicles of satin mice. Combined, these results demonstrate that Hoxc13 and Foxq1 control medulla differentiation through a common regulatory pathway. The apparent regulatory interactions between members of the mammalian Hox and Fox gene families shown here may establish a paradigm for "cross-talk" between these two conserved regulatory gene families in different developmental contexts including embryonic patterning as well as organ development and renewal.

Identification of genes and gene ontology processes critical to skin papilloma development in Tg.AC transgenic mice

This study analyzes gene expression associated with papilloma development in Tg.AC v-Ha-ras transgenic mice and identifies novel genes and biological processes that may be critical to skin carcinogenesis in these mice. Epidermal abrasion was used to synchronously induce epidermal regeneration in FVB/N wild type and transgenic Tg.AC mice. Skin papillomagenesis was uniquely induced in Tg.AC mice, and gene expression profiling was carried out using a 22,000 element mouse DNA microarray. Histological analysis showed that papillomas developed at a high rate by d 30 after abrasion in transgenic animals, while no papilloma developed in wild type mice. Transgene-specific differentially expressed genes were identified at d 30 postabrasion and these genes were annotated using EASE software and literature mining. Annotated and non-annotated genes associated with papilloma development were identified and clustering analysis revealed groups of genes that are coordinately expressed. A number of genes associated with differentiation and development were also physically clustered on mouse chromosome 16, including 16B3 that contains several Stefins and stefin-like genes, and 16A1 containing a number of keratin associated protein genes. Additional analyses presented here yield novel insights into the genes and processes involved in papilloma development in Tg.AC mice.

Human hair keratin-associated proteins (KAPs)

Elucidation of the genes encoding structural proteins of the human hair follicle has advanced rapidly during the last decade, complementing nearly three previous decades of research on this subject in other species. Primary among these advances was both the characterization of human hair keratins, as well as the hair keratin associated proteins (KAPs). This review describes the currently known human KAP families, their genomic organization, and their characteristics of expression. Furthermore, this report delves into further aspects, such as polymorphic variations in human KAP genes, the role that KAP proteins might play in hereditary hair diseases, as well as their modulation in several different transgenic mouse models displaying hair abnormalities.

Comparative analysis of genes downstream of the Hoxd cluster in developing digits and external genitalia

Mammalian Hox genes encode transcription factors that are crucial for proper morphogenesis along the various body axes. Despite their extensive structural and functional characterization, the nature of their target genes remains elusive. We have addressed this question by using DNA microarrays to screen for genes whose expression in developing distal forelimbs and genital eminences was significantly modified in the absence of the full Hoxd gene complement. This comparative approach not only identified specific candidate genes, but also allowed the examination of whether a similar Hox expression pattern in distinct tissues leads to the modulation of the same or different downstream genes. We report here a set of potential target genes, most of which were not previously known to play a role in the early stages of either limb or genital bud development. Interestingly, we find that the majority of these candidate genes are differentially expressed in both structures,although often at different times. This supports the idea that both appendices involve similar genetic controls, both upstream and downstream of the Hox gene family. These results highlight the surprising mechanistic relationship between these rather different body parts and suggest a common developmental strategy to build up the most distal appendicular structures of the body, i.e. the digits and the penis/clitoris.