Secondary Hair Germ Research Articles

Ber-EP4 antigen is a marker for a cell population related to the secondary hair germ.

Ber-EP4 is an antibody to a cell membrane glycoprotein of unknown function. In the skin, Ber-EP4 immunoreactivity has been reported to be localized in structures composed of basaloid epithelial cells, i.e. fetal epithelial germ cells, basal cell carcinoma, and trichoepithelioma as well as eccrine or apocrine ducts. In this study, we further characterized the follicular expression of Ber-EP4 immunoreactivity at different stages of the hair cycle of human terminal hair follicles. In addition, to clarify the location of Ber-EP4(+) cells, we compared the Ber-EP4 immunoreactivity with the expression of keratin 15 and keratin 19. Positive staining by Ber-EP4 was found in the lower part of the epithelial strand of late catagen hair follicles, in the secondary hair germ of telogen hair follicles, and in the matrix of early anagen hair follicles but not in any parts of mature anagen hair follicles. In contrast, the follicular expression of keratin 15 detected by using LHK15 antibody was restricted to two distinct parts of anagen hair follicles, i.e. the outer root sheath above the hair bulb and that of the isthmus including the bulge area, and to the outer root sheath of late catagen and telogen hair follicles. The follicular expressions of keratin 19 and that of keratin 15 were apparently superimposed, whereas keratin 15 expression was more extended. The immunoreactivity of LHK15 antibody and antikeratin 19 antibody against the secondary hair germ of telogen follicles was negative or dim. Our results suggest that Ber-EP4 reacts with the secondary hair germ and possibly a cell population related to the secondary hair germ but not with the presumptive stem cell population as revealed immunohistochemically either by the keratin 15 or keratin 19 expression.

Hair follicle predetermination.

Recent genetic and molecular studies of hair follicle (HF) biology have provided substantial insight; however, the molecular data, including expression patterns, cannot be properly appreciated without an understanding of the basic cellular rearrangements and interactions that underpin HF cyclic transformations. We present a novel interpretation of the major cellular processes that take place during HF cycling--the hypothesis of hair follicle predetermination. This hypothesis is an extension of previous models of HF cellular kinetics but has two critical modifications: the dual origin of the cycling portion of the HF, and the timing of the recruitment of stem cells. A compilation of evidence suggests that the ascending portion of the HF (hair shaft and inner root sheath) arises not from bulge-located HF stem cells that contribute to the formation of only the outer root sheath (ORS), but instead from the germinative cells localized in the secondary hair germ. In middle anagen, upon completion of the downward growth of the HF, cells derived from the bulge region migrate downward along the ORS to reside at the periphery of the HF bulb as a distinct, inactive cell population that has specific patterns of gene expression - 'the lateral disc'. These cells survive catagen-associated apoptosis and, under the direct influence of the follicular papilla (FP), transform into the hair germ and acquire the ability to respond to FP signaling and produce a new hair. Thus, we propose that the specific sensitivity of germ cells to FP signaling and their commitment to produce the ascending HF layers are predetermined by the previous hair cycle during the process of transformation of bulge-derived lateral disc cells into the secondary hair germ.

A role for p75 neurotrophin receptor in the control of apoptosis-driven hair follicle regression.

To examine the mechanisms that underlie the neurotrophin-induced, apoptosis-driven hair follicle involution (catagen), the expression and function of p75 neurotrophin receptor (p75NTR), which is implicated in apoptosis control, were studied during spontaneous catagen development in murine skin. By RT-PCR, high steady-state p75NTR mRNA skin levels were found during the anagen-catagen transition of the hair follicle. By immunohistochemistry, p75NTR alone was strongly expressed in TUNEL+/Bcl2- keratinocytes of the regressing outer root sheath, but both p75NTR and TrkB and/or TrkC were expressed by the nonregressing TUNEL-/Bcl2+ secondary hair germ keratinocytes. To determine whether p75NTR is functionally involved in catagen control, spontaneous catagen development was compared in vivo between p75NTR knockout (-/-) and wild-type mice. There was significant catagen retardation in p75NTR knockout mice as compared to wild-type controls (P<0.05). Instead, transgenic mice-overexpressing NGF (promoter: K14) showed substantial acceleration of catagen (P<0.001). Although NGF, brain-derived neurotrophic factor (BDNF), and neurotrophin 3 (NT-3) accelerated catagen in the organ-cultured skin of C57BL/6 mice, these neurotrophins failed to promote catagen development in the organ-cultured p75NTR null skin. These findings suggest that p75NTR signaling is involved in the control of kerotinocyte apoptosis during catagen and that pharmacological manipulation of p75NTR signaling may prove useful for the treatment of hair disorders that display premature entry into catagen.

E- and P-cadherin expression during murine hair follicle morphogenesis and cycling.

The role of adhesion molecules in the control of hair follicle (HF) morphogenesis, regression and cycling is still rather enigmatic. Since the adhesion molecules E- and P-cadherin (Ecad and Pcad) are functionally important, e.g. during embryonic pattern formation, we have studied their expression patterns during neonatal HF morphogenesis and cycling in C57/BL6 mice by immunohistology and semi-quantitative RT-PCR. The expression of both cadherins was strikingly hair cycle-dependent and restricted to distinct anatomical HF compartments. During HF morphogenesis, hair bud keratinocytes displayed strong Ecad and Pcad immunoreactivity (IR). While neonatal epidermis showed Ecad IR in all epidermal layers, Pcad IR was restricted to the basal layer. During later stages of HF morphogenesis and during anagen IV-VI of the adolescent murine hair cycle, the outer root sheath showed strong E- and Pcad IR. Instead, the outermost portion of the hair matrix and the inner root sheath displayed isolated Ecad IR, while the innermost portion of the hair matrix exhibited isolated Pcad IR. During telogen, all epidermal and follicular keratinocytes showed strong Ecad IR. This is in contrast to Pcad, whose IR was stringently restricted to matrix and secondary hair germ keratinocytes which are in closest proximity to the dermal papilla. These findings suggest that isolated or combined E- and/or Pcad expression is involved in follicular pattern formation by segregating HF keratinocytes into functionally distinct subpopulations; most notably, isolated Pcad expression may segregate those hair matrix keratinocytes into one functional epithelial tissue unit, which is particularly susceptible to growth control by dermal papilla-derived morphogens. The next challenge is to define which secreted agents implicated in hair growth control modulate these follicular cadherin expression patterns, and to define how these basic parameters of HF topobiology are altered during common hair growth disorders.

Basonuclin as a cell marker in the formation and cycling of the murine hair follicle

Basonuclin, a zinc-finger protein, is found in stratified squamous epithelia and hair follicles. In the basal keratinocytes of mouse epidermis, basonuclin is detected mainly in the cytoplasm. During the development of murine hair follicles, this protein concentrates in the nuclei of the basal cells that form the primary hair germs. As follicle morphogenesis proceeds, the epithelial cells possessing nuclear basonuclin invade the dermis and surround the follicular papilla. In mature anagen follicles, nuclear basonuclin is principally restricted to the basal layers of the outer root sheath and bulbar matrix; these regions are known to contain cells capable of proliferation, and to lack the features of terminal differentiation. During catagen, the compartment of cells containing nuclear basonuclin regresses, and in telogen, only a small number of these cells remain to form the secondary hair germ at the follicle base. During the next anagen, this basonuclin-containing population expands and regenerates the hair-producing portion of the follicle. It is concluded that in all hair cycles, the transient segment of the follicle originates from germinative cells possessing nuclear basonuclin.

Two- and three-dimensional demonstrations of morphological alterations of early anagen hair follicle with special reference to the bulge area.

During late telogen to early anagen secondary hair germ is newly formed by the downgrowth of a clubbed column which is indistinguishable from the bulge. Serial vertical sections demonstrated that the early anagen terminal hair follicle formed the new secondary hair germ associated with a lateral protuberance of basaloid cells which could be considered as the bulge of the new hair follicle. Interestingly, the arrector pili muscle bundle was divided into two branches, one inserted into the original clubbed end and the other into this protuberance of the secondary hair germ. CAM5.2-reactive Merkel cells were present not only in the clubbed ends of the old follicle but also in the protuberance of the new hair germ. The formation of the lateral protuberance of the new hair germ preceded the appearance of CAM5.2-reactive Merkel cells in this location. Ks19.1 immunoreactivity was observed from the clubbed end to the upper half of the new hair germ. These phenomena occurred in early anagen before the club hairs were shed. It is postulated that the early anagen hair follicle formed the area within the new hair germ equivalent to the bulge and Merkel cells either moved from the bulge of the old hair follicle or differentiated de novo from immature epithelial cells. Merkel cells or their products in the bulge may serve as attractants for the readjusting arrector pili muscle to anchor to the bulge of the new hair follicle.

Histopathology of cutaneous changes in drug-induced coma.

Present knowledge of the histopathology of cutaneous changes seen in drug-induced coma is very incomplete: Only 1 of the 11 papers on this subject mentions follicular or sebaceous gland damage, with very little attention focused on vascular changes. We made a careful study of serial sections from eight cutaneous biopsy specimens from seven patients who suffered drug-induced coma with the following findings: (a) The secretory portion of the eccrine sweat coil is the epithelium most susceptible to necrosis. It is followed by, ex aequo, eccrine sweat duct, hair follicle, and sebaceous gland, and, lastly, the epidermis. (b) In the eccrine sweat duct, the outer root sheath of the hair follicle, and the epidermis, necrosis does not usually appear first in the outermost (basal cell) layer. (c) Necrosis of the outer root sheath of the telogen "club" follicle is usually more advanced than that of the secondary hair germ, and, at times, a spared anagen bulb can be seen in closest proximity. (d) Vascular changes correlate proportionately with epidermal damage and consist of a largely neutrophilic inflammatory infiltrate and blood vessel wall damage, mainly involving arterioles. Our findings contradict the widely accepted hypothesis that pressure is the main cause of the cutaneous changes in drug-induced coma.

Investigation of germinative cells in generating and renewed anagen hair apparatus in mice using anti-bromodeoxyuridine monoclonal antibody

To elucidate the cell kinetics in generating and renewed anagen hair apparatus in mice, S-phase cells in dorsal skin of new-born and 14 to 25-day-old mice were labeled with bromodeoxyuridine (BrdU) and stained immunohistochemically using anti-BrdU monoclonal antibody. In primary hair germ, lower and outer cells were positively stained. In hair peg, the positive cells were divided into upper and lower portions. In bulbous hair peg, the lower positive cells gathered at the suprapapillary area, whereas the upper positive cells were located in the outer part of the hair apparatus. The latter positive cells were further divided in the middle and upper parts of the epithelial cord. The upper cells were going to form a sebaceous gland. From the suprapapillary group of germinative cells, hair cortex through the innermost cell layer of the outer root sheath were considered to be produced. The positive cells of the outer middle group may be important for elongation of hair apparatus and produce outer root sheath cells. At the end of anagen phase, first the suprapapillary cells became negative and then the outer root sheath cells became negative. BrdU-positive cells reappeared at the bottom of telogen hair apparatus and formed a secondary hair germ. Then, a similar cell kinetics was repeated in the renewed anagen hair apparatus. The germinative cells were separated into a few groups during the generation and cyclic changes of hair apparatus. Each cell group formed the individual part of the hair apparatus in a coordinate fashion, resulting in dynamic changes of the hair apparatus.

Hair anatomy for the clinician

The rational evaluation of hair disorders requires familiarity with follicular anatomy. Hair structure can be easily examined by studying clipped hair shafts, entire hairs gently pulled or forcibly plucked from the scalp, and scalp biopsies (sectioned vertically or transversely). Anatomic features will be different depending on whether a given hair is in the anagen, catagen, or telogen phase. Follicle size will also vary, from the minute vellus hair to the long, thick terminal hair. Each follicle can be divided into distinct regions--bulb, suprabulbar zone, isthmus, and infundibulum. Activity growing (anagen) hairs are characterized by a hair matrix surrounding a dermal papilla; inner and outer root sheaths are present and well developed. A catagen hair can be identified by its markedly thickened vitreous layer and fibrous root sheath, which surrounds an epithelial column; above this column, the presumptive club forms. A telogen hair is distinguished by its fully keratinized club, which is surrounded by an epithelial sac. Below this lies the secondary hair germ and condensed dermal papilla, waiting for the mysterious signal that initiates a new life cycle.

Distribution of Epidermal Growth Factor Receptors in Rat Tissues During Embryonic Skin Development, Hair Formation, and the Adult Hair Growth Cycle

In a previous study on neonatal rat skin (Green MR, Basketter DA, Couchman JR, Rees DA: Dev Biol 100:506-512, 1983) a close positive correlation was found between epidermal growth factor (EGF) receptor tissue distribution and areas of potential epithelial cell proliferation. We now report on the binding distribution of [125I]EGF, representing the tissue localization of available EGF receptors, during embryonic rat skin development including hair follicle formation and the adult hair growth cycle. At 16 days embryonic development a relatively low receptor density is seen over all the epidermal cell layers but by 17 days, with the onset of very rapid epidermal proliferation, labeling increases and becomes restricted to the basal epidermal cells. Between 17 and 20 days embryonic development, available receptors for EGF are consistently absent from epidermal basal cells overlaying the dermal condensates marking the first stage of hair follicle development. This restricted and temporary loss of EGF receptors above these specialized mesenchymal condensates implies a role for the EGF receptor and possibly EGF or an EGF-like ligand in stimulating the epithelial downgrowth required for hair follicle development. In the anagen hair bulb, receptors for EGF are detected over the outer root sheath and the epithelial cell layers at the base of the follicle and show a correlation with the areas of epithelial proliferation in the hair bulb. During the catagen and telogen phases of the hair cycle, receptors are observed in high numbers on all the undifferentiated or dedifferentiating cells of the degenerating epithelial strand and secondary hair germ. Dermal cells are, in general, less heavily labeled than the basal epithelial cells of skin except for the developing striated muscle (panniculus carnosus) in embryonic skin which is more heavily labeled. The data are discussed in terms of a possible role for the EGF receptor and associated EGF or EGF-like ligands in specific areas of epithelial tissue morphogenesis during embryonic skin maturation, hair follicle development, and hair cycling.