Anagen Phase Research Articles

Hair growth effect of minoxidil

The length and size of hair are depend on the anagen term in its hair cycle. It has been reported that the some cell growth factors, such as VEGF, FGF-5S, IGF-1 and KGF, induce the proliferation of cells in the matrix, dermal papilla and dermal papillary vascular system and increase the amount of extra cellular matrix in dermal papilla and then maintain follicles in the anagen phase. On the other hand, negative factors, like FGF-5, thrombospondin, or still unknown ones, terminate the anagen phase. If the negative factors become dominant against cell proliferation factors according to fulfilling some time set by the biological clock for hair follicles, TGF beta induced in the matrix tissues evokes apoptosis of matrix cells and shifts the follicles from anagen to catagen. Androgenetic alopecia is caused by miniaturizing of hair follicles located in the frontal or crown part of scalp and are hereditarily more sensitive to androgen. In their hair cycles, the androgen shortens the anagen phase of follicles and shifts them to the catagen phase earlier than usual. The mode of action of hair growth effect of minoxidil is not completely elucidated, but the most plausible explanation proposed here is that minoxidil works as a sulfonylurea receptor (SUR) activator and prolongs the anagen phase of hair follicles in the following manner: minoxidil (1) induces cell growth factors such as VEGF, HGF, IGF-1 and potentiates HGF and IGF-1 actions by the activation of uncoupled SUR on the plasma membrane of dermal papilla cells, (2) inhibits of TGF beta induced apoptosis of hair matrix cells by opening the Kir 6.0 channel pore coupled with SUR on the mitochondrial inner membrane, and (3) dilates hair follicle arteries and increases blood flow in dermal papilla by opening the Kir 6.0 channel pore coupled with SUR on the plasma membrane of vascular smooth muscle cells.

Expression of Prostaglandin E2 Receptor Subtypes in Mouse Hair Follicles

We investigated the mRNA distribution of the prostaglandin (PG) E2 receptor subtypes and cyclooxygenases (COXs) in hair follicles of the mouse dorsal skin. In the 3-week hair follicles, which are in the anagen phase, EP3 and EP4 mRNA were expressed in the dermal papilla cells and the outer root sheath cells located in the hair bulb region, respectively. In the 8-week hair follicles, which are in the telogen phase, the signals for both EP3 and EP4 mRNAs had disappeared. To study the hair cycle-dependent expression of mRNAs for the EPs and COXs, an area of dorsal hair was depilated from 8-week-old mice. On days 8 and 12 after depilation, EP3 and EP4 mRNA were reexpressed in the dermal papilla cells and the outer root sheath cells, and the induction of COX-2 mRNA was also observed in the outer root sheath cells, the upper area of EP4 expression site. These results suggest that EP3 and EP4 receptors may involve in the development and regrowth of the hair follicles.

Managing Cutaneous Manifestations of Hyperandrogenic Disorders

Cutaneous manifestations of hyperandrogenic disorders (acne, seborrhea, hirsutism and androgenetic alopecia) can be caused by elevated levels of free testosterone or androgen precursors. In women with normal serum levels of testosterone or androgen precursors, enhanced local conversion to testosterone, or to the more potent androgen dihydrotestosterone, may lead to increased androgen activity in the pilosebaceous unit. Large individual variations in the response to normal or elevated androgens suggests considerable differences in local androgen metabolism and androgen receptor-mediated activities, which may partly be related to genetic disposition. Androgens cause opposite effects on hair follicles in the scalp compared with the face and body, and there are large differences in the length of anagen phase. Androgens enhance sebum production and keratinization, prolong the growth phase of face and body hair, stimulate the transformation of vellus to terminal hair, and shorten the anagen phase of scalp hair. Estrogens may antagonize the androgen-induced actions on sebaceous glands and hair follicles. Treatment with oral contraceptives (OCs) reduces the production of androgens and androgen precursors and increases sex hormone-binding globulin, resulting in a decrease of free testosterone levels. According to type and dose, the estrogen and progestogen components of OCs may directly reduce the effect of androgens within sebaceous glands and hair follicles. Therefore, OCs with a predominant estrogen effect may improve mild to moderate forms of acne and seborrhea, hirsutism and androgenetic alopecia, in a time-dependent manner. In women who do not respond satisfactorily, treatment with OCs containing a progestogen with antiandrogenic activity is recommended. In many women with severe acne or hirsutism, a considerable increase in the local concentration of the antiandrogenic progestogen is required to reduce the androgenic interaction with the androgen receptor. For this therapy, an OC containing cyproterone acetate can be used. If necessary, the dose of cyproterone acetate can be increased in a stepwise manner. While androgenetic alopecia is best treated with a low-dose OC containing cyproterone acetate (optimal effect occurs after at least 12 months of therapy), severe acne and hirsutism are significantly improved after 6-12 months of regimens containing high doses of cyproterone acetate (25-100 mg/day). After termination of treatment the disorders may reappear, therefore treatment with suitable low-dose formulations is recommended to maintain the therapeutic effect.

Inducible, reversible hair loss in transgenic mice.

Telogen effluvium is a common type of hair loss. Although the morphological changes associated with telogen effluvium have been well characterized, the underlying molecular mechanisms remain unknown, and no animal models have been developed. We report here that inducible transgenic mice expressing high levels of the transcription factor, tTA (tetracycline transactivator), plus a reporter luciferase gene, show a reversible hair loss phenotype. Skin of these mice exhibits an increase in the number of hair follicles at the telogen phase, but a decreased number of follicles at the anagen phase. These changes resemble skin pathology seen in patients with telogen effluvium, which suggests that the inducible transgenic mice may be useful as a model for this disorder. Moreover, since overexpression of several other transgenes failed to cause skin pathology, the present findings also indicate types of molecular abnormalities that may cause reversible hair loss.

Laser hair removal: guidelines for management.

Laser-assisted hair removal is the most efficient method of long-term hair removal currently available. Several hair removal systems have been shown to be effective in this setting: ruby laser (694nm), alexandrite laser (755nm), diode laser (800nm), intense pulsed light source (590 to 1200nm) and the neodymium:yttrium-aluminium-garnet (Nd:YAG) laser (1064nm), with or without the application of carbon suspension. The parameters used with each laser system vary considerably. All these lasers work on the principle of selective photothermolysis, with the melanin in the hair follicles as the chromophobe. Regardless of the type of laser used multiple treatments are necessary to achieve satisfactory results. Hair clearance, after repeated treatments, of 30 to 50% is generally reported 6 months after the last treatment. Patients with dark colored skin (Fitzpatrick IV and V) can be treated effectively with comparable morbidity to those with lighter colored skin. Although there is no obvious advantage of one laser system over another in terms of treatment outcome (except the Nd:YAG laser, which is found to be less efficacious, but more suited to patients with darker colored skin), laser parameters may be important when choosing the ideal laser for a patient. Adverse effects reported after laser-assisted hair removal include erythema and perifollicular edema, which are common, and crusting and vesiculation of treatment site, hypopigmentation and hyperpigmentation (depending on skin color and other factors). Most complications are generally temporary. The occurrence of hypopigmentation after laser irradiation is thought to be related to the suppression of melanogenesis in the epidermis (which is reversible), rather than the destruction of melanocytes. Methods to reduce the incidence of adverse effects include lightening of the skin and sun avoidance prior to laser treatment, cooling of the skin during treatment, and sun avoidance and protection after treatment. Proper patient selection and tailoring of the fluence used to the patient's skin type remain the most important factors in efficacious and well tolerated laser treatment. While it is generally believed that hair follicles are more responsive to treatment while they are in the growing (anagen) phase, conflicting results have also been reported. There is also no consensus on the most favorable treatment sites.

Dermatotoxicity in the Hypotrichotic(htr) Rabbit Derived from the Japanese White(JW-NIBS) Strain Rabbit.

Utility of Japanese White rabbit mutants with hypotrichosis (htr strain) was investigated in dermal toxicity studies. In the primary irritation study, the primary irritation indices (P.I.I.) by application of hexachlorophene and 3, 3’, 4’, 5-tetrachlorosalicylanilide (TCSA) were higher in the htr rabbits than in the control, haired rabbits. The P.I.I. by application of Tween 80 and sodium lauryl sulfate (SLS) were similar between the htr rabbits and the control rabbits. In the 16-day cumulative irritation study, irritation scores induced by SLS and sodium hydroxide were lower in the htr rabbits than in the control rabbits throughout the observation periods. However, approximately 30% of the dorsal skin of the control rabbits underwent the anagen phase of the hair cycle during the cumulative periods, resulting in difficulty to apply the chemicals and to estimate the skin reactions. In the phototoxicity study, irritation scores of the htr rabbits treated with 8-methoxypsoralen and TCSA were similar to those of the control rabbits. These results revealed advantages of the htr rabbits in the administration of test chemicals and the evaluation of skin reactions, suggesting the usefulness of htr rabbits for dermal toxicity studies.

Lack of the Vitamin D Receptor is Associated with Reduced Epidermal Differentiation and Hair Follicle Growth

The active vitamin D metabolite, 1,25-dihydroxyvitamin D, acting through the vitamin D receptor, regulates the expression of genes in a variety of vitamin D-responsive tissues, including the epidermis. To investigate the role of the vitamin D receptor in mediating epidermal differentiation, we examined the histomorphology and expression of differentiation markers in the epidermis of vitamin D receptor knockout mice generated by gene targeting. The homozygous knockout mouse displayed a phenotype that closely resembles vitamin D-dependent rickets type II in humans, including the development of rickets and alopecia. Hair loss developed by 3 mo after birth and gradually led to nearly total hair loss by 8 mo. Histologic analysis of the skin of homozygous knockout mice revealed dilation of the hair follicles with the formation of dermal cysts starting at the age of 3 wk. These cysts increased in size and number with age. Epidermal differentiation markers, including involucrin, profilaggrin, and loricrin, detected by immunostaining and in situ hybridization, showed decreased expression levels in homozygous knockout mice from birth until 3 wk, preceding the morphologic changes observed in the hair follicles. Keratin 10 levels, however, were not reduced. At the ultrastructural level, homozygous knockout mice showed increased numbers of small dense granules in the granular layer with few or no surrounding keratin bundles and a loss of keratohyalin granules. Thus, both the interfollicular epidermis and the hair follicle appear to require the vitamin D receptor for normal differentiation. The temporal abnormalities between the two processes reflect the apparent lack of requirement for the vitamin D receptor during the anagen phase of the first (developmental) hair cycle, but with earlier effects on the terminal differentiation of the interfollicular epidermis.

Effect of adenovirus-mediated expression of Sonic hedgehog gene on hair regrowth in mice with chemotherapy-induced alopecia.

The Sonic hedgehog (Shh) gene is involved in the initiation of hair growth. We have shown that localized, transient, enhanced expression of the Shh gene in mouse skin mediated by an adenovirus (AdShh) vector accelerates initiation of the anagen (i.e., growth) phase of hair follicle development. Because hair regrowth in chemotherapy-induced alopecia is associated with follicle cell proliferation and active melanogenesis similar to that observed in the anagen phase of normal hair growth, we examined whether AdShh-mediated Shh expression would accelerate hair regrowth in the skin of mice with chemotherapy-induced alopecia. After establishment of cyclophosphamide-induced alopecia, in either 3- or 7-week-old mice, AdShh or a control vector (AdNull) was delivered to dorsal skin by intradermal injection. Hair regrowth and melanogenesis were assessed by histology and gross morphology. Fisher's exact test was used to compare differences in outcomes between AdShh-treated and control (AdNull-treated or not injected with any vector [naive]) mice. All statistical tests were two-sided. Northern blot analysis confirmed enhanced Shh expression after AdShh administration in 7-week-old mice. Two weeks after AdShh administration, the injection site (all of five mice) showed large, anagen-phase hair follicles with a normal distribution of melanin. In contrast, both skin treated with AdNull (all of five mice) and skin from naive mice (all of five mice) showed dystrophic hair follicles with irregular distribution of melanin (P<.001 in both comparisons). Gross morphologic observations confirmed that AdShh-treated mice, but not naive mice or AdNull-treated mice, showed skin darkening at the injection site indicative of entry into anagen phase (P<.001 in both comparisons). AdShh treatment of 3-week-old mice with cyclophosphamide-induced alopecia was followed by accelerated hair follicle recovery (19 of 22 mice); such recovery was not observed at this rate in AdNull-treated or naive skin (P<.001 for both comparisons). Localized, transient, enhanced expression of Shh gene in skin, mediated by an adenovirus vector, might be a future strategy to accelerate hair follicle regrowth after chemotherapy-induced alopecia.

RET tyrosine kinase enhances hair growth in association with promotion of melanogenesis

We first demonstrated that c-Ret protein is transiently expressed mainly in the inner and outer root sheaths of hair follicles soon after birth in the skin of normal C57BL/6 and BALB/c mice. A longer-lasting expression of activated RET protein overlapped the c-Ret expression with some preferential expression in the outer root sheath in close association with increase in the number of S-100 protein-containing cells in the area and excess melanogenesis in and around hair bulbs in the skin of RFP-RET-transgenic mice on a C57BL/6 background (RFP-RET/B6). Hair follicles in the skin of the transgenic mice continuously showed histology of the anagen phase, and the recovery period for the hair of the transgenic mice after shaving was shortened. Such growth promotion was not observed in the case of white hairs of RFP-RET-transgenic mice on a BALB/c background. These results suggest that RET works to extend the anagen phase in association with upregulation of melanin production.

Keratin K6irs is specific to the inner root sheath of hair follicles in mice and humans.

Keratins are a multigene family of intermediate filament proteins that are differentially expressed in specific epithelial tissues. To date, no type II keratins specific for the inner root sheath of the human hair follicle have been identified. To characterize a novel type II keratin in mice and humans. Gene sequences were aligned and compared by BLAST analysis. Genomic DNA and mRNA sequences were amplified by polymerase chain reaction (PCR) and confirmed by direct sequencing. Gene expression was analysed by reverse transcription (RT)-PCR in mouse and human tissues. A rabbit polyclonal antiserum was raised against a C-terminal peptide derived from the mouse K6irs protein. Protein expression in murine tissues was examined by immunoblotting and immunofluorescence. Analysis of human expressed sequence tag (EST) data generated by the Human Genome Project revealed a fragment of a novel cytokeratin mRNA with characteristic amino acid substitutions in the 2B domain. No further human ESTs were found in the database; however, the complete human gene was identified in the draft genome sequence and several mouse ESTs were identified, allowing assembly of the murine mRNA. Both species' mRNA sequences and the human gene were confirmed experimentally by PCR and direct sequencing. The human gene spans more than 16 kb of genomic DNA and is located in the type II keratin cluster on chromosome 12q. A comprehensive immunohistochemical survey of expression in the adult mouse by immunofluorescence revealed that this novel keratin is expressed only in the inner root sheath of the hair follicle. Immunoblotting of murine epidermal keratin extracts revealed that this protein is specific to the anagen phase of the hair cycle, as one would expect of an inner root sheath marker. In humans, expression of this keratin was confirmed by RT-PCR using mRNA derived from plucked anagen hairs and epidermal biopsy material. By this means, strong expression was detected in human hair follicles from scalp and eyebrow. Expression was also readily detected in human palmoplantar epidermis; however, no expression was detected in face skin despite the presence of fine hairs histologically. This new keratin, designated K6irs, is a valuable histological marker for the inner root sheath of hair follicles in mice and humans. In addition, this keratin represents a new candidate gene for inherited structural hair defects such as loose anagen syndrome.

Lectin histochemistry of glycoconjugates in the feline hair follicle and hair

The distribution of glycoconjugate in the feline hair follicle and hair was studied by light and electron microscopic histochemical methods. The hair apparatus was found to contain considerable amounts of complex carbohydrates with different saccharide residues (alpha-D-mannose, beta-D-glucose, alpha-L-fucose, beta-N-acetyl-D-glucosamine). Variations of those were detected in the plasma membrane of the hair follicle cells during the course of their differentiation and keratinization, namely, alph-D-glucose, alpha-L-fucose and beta-N-acetyl-D-glucosamine in the suprabulbar and bulbar regions. The reaction level of sialic acid residues in the plasma membrane decreased in some cell layers during the course of differentiation. The results obtained from the present study indicated that interaction between saccharide residues of neutral carbohydrates and sialyl groups during the anagen phase might contribute to cell keratinization in hair follicles and hairs. It is discussed whether the existence of glycogen in outer root sheath cells might enable these cells to provide other hair apparatus cells with energy when necessary. Moreover, it became obvious from variations in sialyl residue distribution that cell differentiation processes terminate first of all in Huxley's and Henle's layers within the suprabulbar region of the hair follicle, as followed by the hair cortex.

Expression of Calcium-Binding S100 Proteins A4 and A6 in Regions of the Epithelial Sac Associated with the Onset of Hair Follicle Regeneration

In order to elucidate the onset mechanisms of hair regrowth, we characterized the expression of metastasis and cell-growth-associated calcium-binding S100 proteins in the regenerating follicular epithelium. Hair-cycle-dependent expression of S100A4 and S100A6 was found in the epithelial sac regions (bulge area and hair germ) of mouse pelage follicles. Protein localization of S100A4 was confined to the bulge area, the region where the presumed follicular stem cells reside, during the catagen-telogen-anagen transitional periods, whereas S100A6 protein was distributed throughout the epithelial sac regions during anagen phase. Prior to entering anagen phase, however, both S100 mRNAs were upregulated in the epithelial sac. Despite the induction of extensive cell death in the bulge region after plucking, a new hair cycle was initiated following transcription of S100A6 in the hair germ. Upon wounding stimuli, both the outer root sheath and the basal layer of epidermis expressed S100A6 mRNA prior to hyper-proliferation. Once the epithelial sac was induced to transcribe both S100 genes, resting follicles were concomitantly rejuvenated. These results suggest that S100A4 and S100A6 might play important roles in the activation of stem cells at the onset of follicle regeneration.

Relation of Skin Polyamines to the Hairless Phenotype in Transgenic Mice Overexpressing Spermidine/Spermine N1-Acetyltransferase

We recently generated a transgenic mouse line with activated polyamine catabolism due to overexpression of spermidine/spermine N1-acetyltransferase. Phenotypic changes in these animals included permanent loss of hair at the age of 3 wk. We have now further explored development of hair loss during early postnatal life. The first hair cycle appeared to be completed normally in the transgenic animals. At postnatal day 15, although macroscopically indistinguishable from their syngenic littermates, the transgenic animals already showed microscopically signs of hair follicle degeneration. Wild-type mice started their second anagen phase at day 27, whereas the transgenic animals did not display functional hair follicles at that time. Hair follicles were replaced by dermal cysts and epidermal utriculi. Analysis of skin polyamines revealed that the transgenic animals continuously overaccumulated putrescine. The view that an overaccumulation of putrescine was related to the disturbed hair follicle development was strengthened by the finding that doubly transgenic mice overexpressing, both spermidine/spermine N1-acetyltransferase and ornithine decarboxylase and with extremely high levels of putrescine in the skin, showed distinctly more severe skin changes compared with the singly transgenic animals. Interest ingly, in spite of their hairless phenotype, the spermidine/spermine N1-acetyltransferase transgenic mice, were significantly more resistant to the development of papillomas in response to the two-stage skin carcinogenesis. Analysis of skin polyamines indicated that the syngenic mice tripled their spermidine content when exposed to promotion, whereas the transgenic animals showed only modest changes. These results suggest that putrescine plays a pivotal part in normal hair follicle development.

Mrp3, a mitogen-regulated protein/proliferin gene expressed in wound healing and in hair follicles.

During cutaneous wound healing, a marked increase in the local expression of growth factors results in increased migration and proliferation of the cells responsible for tissue repair. The mitogen-regulated protein (MRP)/proliferin proteins are growth factors and angiogenesis factors. Here it is demonstrated that Mrp3 is induced in wound edge keratinocytes during cutaneous wound healing and also temporally appears in the outer root sheath of the hair follicle during the late anagen phase of the hair cycle. In cultured keratinocytes, Mrp3 is induced by keratinocyte growth factor, but not by epidermal growth factor or by transforming growth factor type alpha. Transgenic mice, expressing lacZ under the combined control of the cytomegalovirus immediate early enhancer and the Mrp3 flanking sequences, demonstrate wound- and hair cycle-induced transgene expression. These results show that elements within the flanking regulatory sequences of the Mrp3 gene are involved in the activation of Mrp3 in response to these events. The results reported here suggest that MRP3 may participate in wound healing and hair follicle cycle as a growth factor and/or angiogenesis factor.

Biological actions of oligomeric procyanidins: Proliferation of epithelial cells and hair follicle growth

Hair is composed of epithelial and mesenchymal cells. Interactions between epithelial and mesenchymal cells are considered to be important both in hair morphogenesis in embryonic skin and in the progress of the hair cycle through the anagen, catagen, and telogen phases in adult skin. 1 Inner root sheath cells, outer root sheath cells, and hair matrix cells are all types of epithelial cell. Dermal papilla cells are a type of mesenchymal cell. 2 These mesenchymal-epithelial interactions are assumed to stimulate stem cells to proliferate, to induce the anagen phase in the hair cycle, and to produce hair. Stem cells are hypothesized to exist in the bulge area in the outer root sheath, 3 in the matrix, 4 or between the bulge and the matrix 5; however, stem cell sites have not been elucidated positively. Hair growth stimulants are expected to prolong the anagen phase or to promote hair epithelial cell proliferation following anagen induction. 6 For in v i t ro evaluation of hair growth stimulants, tissue culture methods 7 and organ culture methods using dissected hair follicles 8 or sectioned skin 9 have been reported. For in v i v o evaluation of hair growth stimulants, methods using murine models such as C3H mouse, l° C57BL mouse, II or nude mousel2; rabbit13; and stump-tailed macaque 14 have been reported.

Differentiation of hair growth cycle from scalp hair roots for the diagnosis of glucose-6-phosphate dehydrogenase deficiency in neonates.

Hair analysis can be used as a screening tool in the diagnosis of genetic diseases. The scalp hair roots of 67 normal neonates and 39 neonates with glucose-6-phosphate dehydrogenase (G6PD) deficiency were analysed using Fourier transform infrared (FT-IR) microspectroscopy to differentiate the stages of the hair growth cycle and to diagnose the genetic disorder on the basis of spectral differences. We have demonstrated that FT-IR microspectroscopy is a rapid and effective noninvasive diagnostic method to differentiate scalp hair roots of normal neonates into the anagen, catagen or telogen phases of the hair growth cycle, using IR spectral differences within the 3000-2800 cm(-1) region and the IR peak area ratio of 2854 cm(-1)/2873 cm(-1) or 1084 cm(-1)/amide II band (p<0.001). Moreover, G6PD-deficient neonates could be accurately diagnosed from telogen phase hair roots owing to significant differences in IR peak area ratios of 2854 cm(-1)/2873(-1) or 1084 cm(-1)/amide II band compared to normal values in healthy neonates. The result suggests that the application of FT-IR microspectroscopy may be capable not only of differentiating the hair growth cycle into anagen, categen or telogen phases but also of detecting G6PD deficiency. Hair root analysis promises to be a useful complement to serum and urine analysis in the diagnosis of genetic diseases.

μ-Crystallin, Thyroid Hormone-binding Protein, is Expressed Abundantly in the Murine Inner Root Sheath Cells

In an attempt to investigate the genes expressed during the development of mouse hair follicles, we employed RNA differential display and identified a cDNA encoding micro-crystallin, that is a major component of kangaroo lens and a cytosolic NADP-regulated thyroid hormone-binding protein in human kidney. In northern blot study, mu-crystallin transcripts were detected in skin at the highest level among the mouse tissues, whereas lower but detectable in the eye, brain, kidney, heart, lung, and liver. Furthermore, in mouse skin, the gene expression of mu-crystallin followed hair cycle fundamentally, increased significantly during mid- and late anagen phases and decreased during the catagen, telogen, and early anagen phases. In situ hybridization revealed that mu-crystallin gene starts to be activated in hair cone of anagen III, and that in anagen VI, its expression is detected predominantly in the cuticle layer of the inner root sheath from the upper hair bulb to the middle portion of the keratogenous zone and in the Huxley's layer through the keratogenous zone. The expression was not detected in catagen, telogen, and early anagen hair follicles, and any other skin components. These results suggest the possible involvement of mu-crystallin in the development of mouse hair follicles during the anagen phase.

Congenital hypotrichosis due to short anagen

Two children with congenital hypotrichosis are described. Both presented with persistent short, fine hair since birth. Evidence is provided that the short hair observed in these patients is due to a short anagen phase of the hair cycle, with a normal rate of hair growth. Shortening of the anagen phase of the scalp hair cycle leads to a decrease in the maximal hair length and an increase in the number of hairs in telogen, resulting in an increase in hair shedding. Scanning electron microscopy showed a widely spaced cuticular pattern, a finding typically seen in hair of thin calibre. One patient had affected family members with an apparently autosomal dominant mode of inheritance. The disorder appears to resolve spontaneously during puberty and adulthood.

Gene Structure, Chromosomal Localization, and Expression Pattern of Capn12, a New Member of the Calpain Large Subunit Gene Family

We report the identification of mouse Capn12, a new member of the calpain large subunit gene family. It possesses potential protease and calcium-binding domains, features typical of the classical calpains. In situ hybridization and Northern blot analysis demonstrate that during the anagen phase of the hair cycle the cortex of the hair follicle is the major expression site of Capn12. The gene was sequenced in its entirety and consists of 21 exons spanning 13 kb with an exon–intron structure typical of the calpain gene family. The last exon of the mouse Actn4 gene overlaps the 3′ end of Capn12 but in the opposite orientation. This overlap between the two genes is conserved in the human genome. Three versions of the Capn12 mRNA transcript were identified. They occur as a result of alternative splicing, and two of these encode a protein lacking the C-terminal calmodulin-like domain. Radiation hybrid mapping localized Capn12 to mouse chromosome 7, closely linked to a marker positioned at 10.4 cM. Refined mapping of Capn5, also previously localized to chromosome 7, indicated that it was not closely linked to Capn12, mapping tightly linked to a marker positioned at 48.5 cM.

Melanocyte subpopulation turnover during the human hair cycle: an immunohistochemical study.

The human hair cycle is characterized by successive phases of growth and involution that imply tissue regression and regeneration. As a consequence, the hair melanin unit has to be renewed in a cyclic manner. Actually, the behavior of human hair follicle melanocytes throughout the hair cycle has been poorly studied. Thus, the origin of melanocytes present in the bulb after human hair regeneration is still not clarified, and neither are the events that control the melanin biosynthesis activity in the human hair bulb. In this study, we showed at the cellular level that in human pigmented hair follicles, the expression of tyrosinase and tyrosinase-related protein-1 (TRP-1) was detectable during the anagen phases III/IV through VI, only in those melanocytes which were located in the bulb. During the catagen phase, the two evaluated melanogenic enzymes were detectable no more, although melanocytes were still present in the preceding bulbar area. The epithelial column of catagen follicles and the capsule of telogen follicles also contained inactive melanocytes as evidenced by pMel-17 labeling. At the induction of a new anagen hair follicle, some melanocytes were committed to cell division, but only when located in the nascent bulb close to the dermal papilla. Our results emphasize the close relationship between melanogenesis and the hair cycle and suggest that in humans, melanogenesis is restricted to anagen hair follicles not because of the regulation of tyrosinase activity, but because of melanogenic enzyme expression, e.g., tyrosinase and TRP-1. Furthermore, the fact that in the newly developing anagen hair follicles, cell-division commitment and tyrosinase and TRP-1 expression were observed in melanocytes only when located in the nascent bulb suggests a highly regio-specific melanocyte stimulation in early the anagen phase.