Secondary Hair Research Articles

Wounding mobilizes hair follicle stem cells to form tumors

A wide variety of human cancers are associated with injury. Although stem cells participate in tissue regeneration after wounding, it is unclear whether these cells also contribute to epithelial tumors. Human basal cell carcinomas (BCCs) are associated with misactivation of Hedgehog (Hh) signaling, commonly through acquisition of mutations in Smoothened (Smo). We have found that expression of an activated form of Smo by stem cells of the hair-follicle bulge and secondary hair germ does not induce robust Hh signaling or produce BCCs. However, wounding recruits these cells from the follicle to the wound site, where downstream Hh signal transduction is derepressed, giving rise to superficial BCC-like tumors. These findings demonstrate that BCC-like tumors can originate from follicular stem cells and provide an explanation for the association between wounding and tumorigenesis.

Activated Kras Alters Epidermal Homeostasis of Mouse Skin, Resulting in Redundant Skin and Defective Hair Cycling

Germline mutations in the RAS-mitogen-activated protein kinase (RAS/MAPK) pathway are associated with genodermatoses, characterized by cutaneous, cardiac, and craniofacial defects, and cancer predisposition. Whereas activating mutations in HRAS are associated with the vast majority of patients with Costello syndrome, mutations in its paralog, KRAS, are rare. To better understand the disparity among RAS paralogs in human syndromes, we generated mice that activate a gain-of-function Kras allele (Lox-Stop-Lox (LSL)-Kras(G12D)) in ectodermal tissue using two different Cre transgenic lines. Using Msx2-Cre or ligand-inducible keratin 15 (K15)-CrePR, the embryonic effects of activated Kras were bypassed and the effects of Kras(G12D) expression from its endogenous promoter were determined. We found that Kras(G12D) induced redundant skin, papillomas, shortened nails, and hair loss. Redundant skin was associated with basal keratinocyte hyperplasia and an increase in body surface area. Paradoxically, Kras(G12D) also prevented hair cycle activation. We find that Kras(G12D) blocks proliferation in the bulge region of the hair follicle, when activated through Msx2-Cre but not through K15-CrePR. These studies reveal that KRAS, although infrequently involved in RAS/MAPK syndromes, is capable of inducing multiple cutaneous features that grossly resemble human RAS/MAPK syndromes.

Hair density in the Eurasian otter Lutra lutra and the Sea otter Enhydra lutris

The hair density of adult Eurasian otters Lutra lutra (Linnaeus, 1758) and sea otters Enhydra lutris (Linnaeus, 1758) was analysed using skin samples taken from frozen carcasses. Lutra lutra exhibited a mean hair density of about 70 000 hairs/cm2 (whole body, appendages excepted), the mean individual density ranging from about 60 000 to 80 000 hairs/cm2. The dominant hair type were secondary hairs (wool hairs), the hair coat comprising only 1.26% of primary hairs (PH). Secondary hair (SH) density remained constant over the body (appendages excepted), whereas a few variations in PH density were observed. Neither an influence of the sex, nor a seasonal variation of the hair coat was found, moulting seems to be continuous. Enhydra lutris had a hair density between 120 000 and 140 000 hairs/cm2, the primary hairs representing less than 1% within the hair coat. Hair density remained quite constant over the regions of the trunk but was lower at the head (about 60 000 hairs/cm2 on the cheek). The hair follicles were arranged in specific groups with different bundles of varying size, normally comprising dominant numbers of wool hair (SH) follicles. Invariably there was always a large central primary hair follicle and numerous sebaceous glands between the bundles and principally around the PH follicles. The results are discussed related to possible ecological influences on hair coat density.

Hair growth in a skin graft from a glabrous donor site in a child

An 8-year-old girl with brown hair presented with a large (8×10 cm) congenital hairy naevus involving her left cheek and temple. Due to the size of the lesion, excision was planned in two stages, in combination with tissue expansion of her left groin skin for Wolfe grafting. The lesion was excised in its inferomedial portion and a fullthickness skin graft applied. Care had been taken to harvest the graft lateral to the normal growth area of secondary sexual hair. Two weeks later, it was noted that a few small areas of the graft had not taken. These areas underwent necrosis and healing by secondary intention (Fig. 1). The patient found these areas to be extremely painful and complained of hypersensitivity. Then, upon review at 3 months, hair was seen on the graft (Fig. 2), whereas the naevus hair had been thick and dark, the stimulated hair was fine and depigmented. No hair was noted in the donor groin region (Fig. 3). The patient was referred for laser depilation treatment; however, this was unsuccessful due to the lack of hair pigmentation. Despite this, the patient and her family were pleased with the improvement in her appearance.

Immunolocalization of Wnt5a during the hair cycle and its role in hair shaft growth in mice

Previous studies have shown that the Wnt signaling pathway plays an important role in the growth and development of hair follicles. It has been generally accepted that Wnt5a, a non-canonical Wnt gene, inhibits the Wnt/β-catenin signaling pathway. Several reports have addressed its mRNA expression in embryonic and postnatal hair follicles, but its exact role in the growth of hair follicles is currently unknown. In this study, we investigated the immunolocalization of Wnt5a protein in pelages of the dorsal skin and whisker follicles of mice. We found that in the anagen phase, dermal papilla cells showed the highest staining levels of Wnt5a protein, while in the catagen and the telogen phases the staining levels were lower. During the growth stage, Wnt5a protein was prominently located in the matrix and precortex cells in addition to the inner root sheath, outer root sheath and the dermal papilla. As the hair cycle progresses, the immunostaining of Wnt5a was gradually decreased in the catagen phase and was located in the bulge and secondary hair germ in the telogen phase. This Wnt5a immunostaining profile was consistent between dorsal skin pelages and whisker follicles. Furthermore, in an in vitro study using whisker follicle organ culture, we demonstrated that the growth of the hair shaft was significantly inhibited by adenovirus Wnt5a. Our findings suggest that Wnt5a is a dynamic factor in the hair cycle and it is important for the regulation of hair shaft growth.

Cyclic Expression of Lhx2 Regulates Hair Formation

Hair is important for thermoregulation, physical protection, sensory activity, seasonal camouflage, and social interactions. Hair is generated in hair follicles (HFs) and, following morphogenesis, HFs undergo cyclic phases of active growth (anagen), regression (catagen), and inactivity (telogen) throughout life. The transcriptional regulation of this process is not well understood. We show that the transcription factor Lhx2 is expressed in cells of the outer root sheath and a subpopulation of matrix cells during both morphogenesis and anagen. As the HFs enter telogen, expression becomes undetectable and reappears prior to initiation of anagen in the secondary hair germ. In contrast to previously published results, we find that Lhx2 is primarily expressed by precursor cells outside of the bulge region where the HF stem cells are located. This developmental, stage- and cell-specific expression suggests that Lhx2 regulates the generation and regeneration of hair. In support of this hypothesis, we show that Lhx2 is required for anagen progression and HF morphogenesis. Moreover, transgenic expression of Lhx2 in postnatal HFs is sufficient to induce anagen. Thus, our results reveal an alternative interpretation of Lhx2 function in HFs compared to previously published results, since Lhx2 is periodically expressed, primarily in precursor cells distinct from those in the bulge region, and is an essential positive regulator of hair formation.

Dkk4 and Eda Regulate Distinctive Developmental Mechanisms for Subtypes of Mouse Hair

The mouse hair coat comprises protective “primary” and thermo-regulatory “secondary” hairs. Primary hair formation is ectodysplasin (Eda) dependent, but it has been puzzling that Tabby (Eda -/y) mice still make secondary hair. We report that Dickkopf 4 (Dkk4), a Wnt antagonist, affects an auxiliary pathway for Eda-independent development of secondary hair. A Dkk4 transgene in wild-type mice had no effect on primary hair, but secondary hairs were severely malformed. Dkk4 action on secondary hair was further demonstrated when the transgene was introduced into Tabby mice: the usual secondary follicle induction was completely blocked. The Dkk4-regulated secondary hair pathway, like the Eda-dependent primary hair pathway, is further mediated by selective activation of Shh. The results thus reveal two complex molecular pathways that distinctly regulate subtype-based morphogenesis of hair follicles, and provide a resolution for the longstanding puzzle of hair formation in Tabby mice lacking Eda.

Hair Follicles Stimulation Effects of Gelatin Nanofibers Containing Silver Nanoparticles

In the present work we studied gelatin nanofibers containing silver nanoparticles of 14 +/- 6 nm mean diameter, prepared by electrospinning. The electrospinnable solution was obtained by drop-wise adding a AgNO3/acetic acid solution to gelatin which had previously been dissolved in a mixture of formic acid and acetic acid. The silver metallic nanoparticles were formed due to the reducing action of the formic acid. The resulted material was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray diffraction (XRD). Subcutaneous implants in rabbits demonstrated that the gelatin nanofibers containing silver nanoparticles were resorbed with no inflammatory reactions. An increased number of secondary hair follicles developed in tissue regions close to implants, suggesting the existence of a stimulation effect of silver nanoparticles on hair follicles.

Characterization and expression analysis of KAP7.1, KAP8.2 gene in Liaoning new-breeding cashmere goat hair follicle

Keratin-associated protein is one of the major structural proteins of the hair, whose content in hair has important effect on the quality of cashmere. In order to study the relationship between HGTKAP gene expression and cashmere fineness, the quantitative real-time RT-PCR (qRT-PCR) was firstly used to detect the levels of KAP7.1, KAP8.2 gene expression in the primary and secondary hair follicles; semi-quantitative RT-PCR was used to detect whether KAP7.1, KAP8.2 gene are expressed in heart, liver, spleen, lung, kidney tissues; and insitu hybridization(ISH) to detect KAP7.1 gene expression location. qRT-PCR result showed that the expression of both KAP7.1 and KAP8.2 gene in the secondary hair follicles are significantly higher than that in the primary follicles, relative quantitative analysis obtained that KAP7.1 was 2.28 times, while KAP8.2 was 2.71 times. Semi-quantitative RT-PCR results revealed that KAP 7.1 and KAP8.2 mRNA were not detected in the heart, liver, spleen, lung and kidney tissues, demonstrating that KAP7.1 and KAP8.2 were specially expressed in hair follicles, participating in hair formation. Moreover, KAP7.1 gene has a strong expression in the cortical layer, inner root sheath of the primary follicles and the cortical layer, inner root sheath and hair matrix of the secondary hair follicles by ISH analysis. Taken together, the evidence presented here indicated that in the formation of cashmere and wool, differential expression of these two genes in the primary and secondary hair follicles may have an important role in regulating the fiber diameter.

A Revaluation of Trichofolliculoma: The Histopathological and Immunohistochemical Features

Few investigations on the histopathology of trichofolliculoma (TF) have so far included an immunohistochemical study. To seek new insight into TF with a revaluation of the histopathological features and an investigation of the immunohistochemical profile, 14 TFs were revaluated for the histopathology and the immunohistochemical profile of various cytokeratins (CKs), hair follicle stem cell markers, and others. The CK15 expression was upregulated in the basal cells from the primary cystic structures beyond to secondary follicles without expression of CK19. CK16 and CK17 were positive in the suprabasal cells of the primary cystic structures and the immature secondary hair follicles. No exact isthmus/bulge region was seen in the anagen secondary hair follicles, and newly developed (tertiary) hair follicles arose randomly from the involuting secondary follicles. Ber EP4 expression was generally weakened in the secondary or tertiary hair germ-like structures. The size of secondary hair follicles varied from vellus hair follicles to terminal hair follicles, even though no lesions located on the regions where the terminal hairs develop were included in this study. S-100 protein-positive wavy spindle cells were accidentally found in the surrounding connective tissue of the secondary follicles in 2 TF lesions. TFs were characterized by the proliferation of abnormal CK15-positive hair follicle stem cells, which basically differentiated toward the outer root sheath and attempting to make hair but losing the proper differentiation. The control of the size of the anagen hair follicles and the regular hair cycle were also disordered.

In vitro methodology, hormonal and nutritional effects and fibre production in isolated ovine and caprine anagen hair follicles

Mammalian hair follicles are complex multicellular structures in the skin, which produce hair fibre under the influence of locally produced and systemic signalling systems. Investigation to determine mechanisms of regulation, follicular responses and the importance of nutritional supply have utilised a number of in vivo and in vitro approaches. Included in these are studies on isolated intact anagen secondary follicles singly or in groups with incubation in culture medium. These utilise techniques developed for investigation of follicles from human skin. Results from selected studies reviewed here demonstrate differences in capacity for hair growth and protein synthesis between secondary follicles from Angora and cashmere-bearing goats. Mohair follicles were shown to exhibit faster hair shaft elongation both in vivo and in vitro, to have greater DNA content per follicle and to deposit significantly more protein per follicle and per unit of DNA. Incubation of anagen mohair and cashmere follicles in the presence of melatonin or prolactin showed positive responses in hair shaft growth and protein synthesis to both signalling molecules. This result indicated directly acting effects on the follicle in addition to any indirect effects arising at a whole animal level in response to, for example, variation in photoperiod. Similarly, epidermal growth factor was shown to alter elongation and protein synthesis in mohair follicles and to produce, at higher concentration, club hair structures similar to effects observed in other species. The vitamin biotin was shown to be important in maintaining viability of isolated sheep secondary hair follicles where supplementation increased the proportion continuing to grow. Effects on growth and apparent protein synthesis suggested comparatively lesser effects on follicles, which remained viable. Histology on follicles indicated effects of biotin deficiency in reducing proliferation of basal keratinocytes. The final study, included in this review, demonstrated that supply of the essential sulphur-containing amino acid l-methionine was necessary to maintain the viability and growth of mohair follicles. l-cysteine was not required in the presence of l-methionine, although there was evidence of an optimisation when both amino acids were present in adequate concentrations. Consideration is given to the importance of transport mechanisms and capacity to utilise absorbed nutrients when considering optimising nutritional supply to individual follicles. These may then provide targets for attainment in applied nutrition of animals in vivo.

Characterization of BMP2 gene expression in embryonic and adult Inner Mongolia Cashmere goat (Capra hircus) hair follicles

Mammalian skin consists of thousands of hair follicles, each undergoing continuous regenerative cycling including anagen, catagen and telogen. Hair follicle morphogenesis results in the appearance of fur in animals. Increasing evidence suggests that bone morphogenetic proteins (BMP) play an important role in the induction and progression to various stages of the hair follicle cycle. In this study, BMP2 mRNA expression level was investigated from different phases using real-time PCR (qRT-PCR) and localized with in situ hybridization in adult Inner Mongolia Cashmere goat. qRT-PCR revealed that the expression of BMP2 in early anagen was 27.8 times greater than expression during late anagen phase. The in situ hybridization detected BMP2 expressed at days 75 and 115 in both primary and secondary hair follicles during the embryonic period. Further, BMP 2 was expressed in primary hair follicles in late telogen and in secondary hair follicles in early anagen in adult goat. However, it was found to be absent in both primary and secondary hair follicle in late anagen in the adult goat. BMP2 expression was found to be higher in late telogen and early anagen phases and lower in late anagen in the goat’s skin and hair follicle, suggesting that it may have a role in the regeneration of hair follicle.Key words: BMP2, expression, Cashmere goat, hair follicle, in situ hybridization, real-time PCR

Black holes in higher dimensional gravity theory with corrections quadratic in curvature

Static spherically symmetric black holes are discussed in the framework of higher dimensional gravity with quadratic in curvature terms. Such terms naturally arise as a result of quantum corrections induced by quantum fields propagating in the gravitational background. We focus our attention on the correction of the form ${\mathcal{C}}^{2}={C}_{\ensuremath{\alpha}\ensuremath{\beta}\ensuremath{\gamma}\ensuremath{\delta}}{C}^{\ensuremath{\alpha}\ensuremath{\beta}\ensuremath{\gamma}\ensuremath{\delta}}$. The Gauss-Bonnet equation in four-dimensional spacetime enables one to reduce this term in the action to the terms quadratic in the Ricci tensor and scalar curvature. As a result the Schwarzschild solution which is Ricci flat will be also a solution of the theory with the Weyl scalar ${\mathcal{C}}^{2}$ correction. An important new feature of the spaces with dimension $D>4$ is that in the presence of the Weyl curvature-squared term a necessary solution differs from the corresponding ``classical'' vacuum Tangherlini metric. This difference is related to the presence of secondary or induced hair. We explore how the Tangherlini solution is modified by ``quantum corrections,'' assuming that the gravitational radius ${r}_{0}$ is much larger than the scale of the quantum corrections. We also demonstrated that finding a general solution beyond the perturbation method can be reduced to solving a single third order ordinary differential equation (master equation).

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.

Verlaufskontrolle bei andrologischen Patienten unter HCG/HMG-Therapie unter besonderer Berücksichtigung des Spermiogramms und der somatischen Entwicklung

Between 1971 and 1976, 47 patients were treated in the department for andrology with daily alternating HCG/HMG injections. This treatment provides an attempt for examination of effects of a combined HCG/HMG therapy with a larger group of patients. As a condition for the HCG/HMG treatment a testicular biopsy was performed. It could be shown that in 70% of the cases there was no normal tabulus diameter, that the germinal epithelium was mostly low, and that in the germinal epithelium in 53,8% of the cases a spermiogenesis was demonstrable, but only in 3% of the cases sufficient spermatozoa existed. Most of the patients presented a disorganisation and desquamation of the germinal epithelium. During treatment no further testicular biopsies were made so that no statements can be given on the change of the tubules. Concerning the observation of the patients' sperm count it could be proved that, as a result of the HCG/HMG treatment, 33,3% of the patients showed an increase of motility and in 37,5% of the patients the number of spermatozoa increased. The paper describes two patients showing normal sperm count already after 8 to 12 weeks. Furthermore de Kretsers' observations on large decrease of spermatozoal number after the 150th day of treatment, and Paulsens' observations on hot flushes in some patients due to interruption of treatment, could be confirmed. The somatic development during HCG/HMG treatment showed an increase of volume of the testicles and an increase of the secondary hair. These changes also appeared already within 12 weeks after the beginning of treatment. In 38,5% of studied cases erections and ejaculations appeared already after 8 to 12 weeks as far as this didn't occur before treatment. In four cases pregnancy resulted from treatment. There was one early abortion. In all other cases gravidity and birth were normal. Only in one case negative side effects as a lack of concentration resulted. This study provides evidence that an alternating HCG/HMG treatment can be quite successful. Gonadotropin levels and the result of testicular biopsy have to be considered for clinical evaluation of treatment and therapeutic results.

Analysis of the Temporal Requirement for Eda in Hair and Sweat Gland Development

EDA signaling is important in skin appendage initiation. Its possible involvement in appendage subtype determination and postinduction stage appendage development, however, has not been studied systematically. To address these issues we manipulated Eda-A1 transgene expression in a tetracycline-regulated conditional mouse model, where the transgene is the only source of active ectodysplasin (Eda). We find that Eda-A1 restores sweat glands and all hair subtypes in Tabby, but each requires its action at an idiosyncratic time of development: by E17 for guard, by E19 for awl, and starting at E18 for zigzag/auchen hair. Guard and awl hairs were indistinguishable from their wild-type counterparts; but restored zigzag and auchen hairs, although recognizable, were somewhat smaller and lacked characteristic bends. Notably, secondary hair follicle formation of awl, auchen, and zigzag hairs required higher Eda-A1 expression level than did guard hair or sweat glands. Furthermore, Eda-A1 expression is required until the early dermal papilla stage for guard hair germs to make follicles, but is dispensable for their maturation. Similarly, sweat gland pegs require Eda-A1 at an early stage to form mature glands. Thus we infer that EDA signaling is needed for the determination and development of various skin appendages at spatiotemporally restricted intervals.

The River of Stem Cells

In this issue of Cell Stem Cell, Greco et al. (2009) characterize the hair germ as a novel stop between bulge stem cell and transient amplifying cells during hair regeneration. The work implies stem cell states can be regulated to form different numbers of intermediate stops, depending on physiological requirements.

The Tcl1 oncogene defines secondary hair germ cells differentiation at catagen–telogen transition and affects stem-cell marker CD34 expression

Overexpression of the TCL1 gene family plays a role in the onset of T-cell leukemias in mice and in humans. The Tcl1 gene is tightly regulated during early embryogenesis in which it participates in embryonic stem (ES)-cells proliferation and during lymphoid differentiation. Here, we provide evidences that Tcl1 is also important in mouse hair follicle (HF) and skin homeostasis. We found that Tcl1(-/-) adult mice exhibit hair loss, leading to alopecia with extensive skin lesions. By analysing Tcl1 expression in the wild-type (wt) skin through different stages of hair differentiation, we observe high levels in the secondary hair germ (HG) cells and hair bulges, during early anagen and catagen-telogen transition phases. The loss of Tcl1 does not result in apparent skin morphological defects during embryonic development and at birth, but its absence causes a reduction of proliferation in anagen HFs. Importantly, we show the that absence of Tcl1 induces a significant loss of the stem-cell marker CD34 (but not alpha6-integrin) expression in the bulge cells, which is necessary to maintain stem-cell characteristics. Therefore, our findings indicate that Tcl1 gene(s) might have important roles in hair formation, by its involvement in cycling and self-renewal of transient amplifying (TA) and stem-cell (SC) populations.

Sequence of a Cashmere goat type I hair keratin gene and its expression in skin

The keratin family includes the epithelial (soft) keratins and the hair (hard) keratins, which can be divided into two subfamilies—the acidic type I and the basic or neutral type II. A cDNA is isolated and sequenced from a cDNA library constructed with poly (A) +RNA derived from the goat skin. Because the gene sequence of the known type I hair keratins 8C1 is in accordance with that of the hHa1, this keratin can be identified as the goat hair keratin gHa1 cDNA (GenBank Accession No. AY510110.1). The 413 amino acid sequence derived is compared with the Sheep 8C1 type I mRNA and they exhibit the highest homology (97.8%). In in situ hybridization, it has revealed a strong expression in the cortex of both primary and secondary hair follicles.

The Ludwig pattern of androgenetic alopecia is due to a hierarchy of androgen sensitivity within follicular units that leads to selective miniaturization and a reduction in the number of terminal hairs per follicular unit

Hair follicles exist within follicular units (FUs). In utero the central primary hair follicles are surrounded by smaller secondary follicles. Each FU is nourished by a single arborizing arrector pili muscle that attaches circumferentially around the primary follicle with variable attachment to other follicles. Androgenetic alopecia (AA) miniaturizes susceptible scalp hair follicles in a distinctive and reproducible fashion manifesting in different patterns between men and women. We hypothesized that there is an additional layer to the patterning in AA, with a hierarchy of susceptibility within FUs to AA, and that the diffuse hair loss seen in women with AA is due to a reduction in the number of terminal hairs per FU rather than uniform miniaturization of entire FUs. We compared the mean numbers of FUs and terminal hairs per FU in 4-mm scalp punch biopsies in 24 women with AA with those in 21 controls. There was no significant difference in the number of FUs; however, women with AA had 2.40 terminal hairs per FU compared with 3.38 in the control group (P=0.0001) associated with a mean increase of 0.6 vellus hairs per FU. Complete miniaturization of all hairs within the FU was not seen. Diffuse hair loss in women with AA is due to a reduction in the number of terminal hairs per FU and an increase in the number of vellus hairs. This supports the hypothesis of a hierarchy of susceptibility within FUs to AA. Further investigation is required to ascertain whether secondary and tertiary hair follicles are more susceptible than primary follicles.