Primary Hair Follicles Research Articles

Improved fetal hair follicle development by maternal supplement of selenium at nano size (Nano-Se)

To investigate the effect of maternal and dietary selenium on antioxidant status and hair follicle development in 110-day fetal skin from cashmere goats, eighty selected cashmere goats (n=80) were randomly divided in two groups, C group (fed with the basal diet) and S group (fed with the basal diet with 0.5mg/kg Nano-Se). Nano-Se was supplemented from 30days prior to gestation to fetal day 110. Samples of fetus on day 110 have shown that the expression of GSH-Px, IGF-1 and IGF-1R, as well as the activities of GSH-Px and SOD, were significantly higher in S group than those in C group. The MDA level was significantly lower in S group. The concentrations of IGF-1, Se and T-AOC in both fetal serum and skin were significantly increased in S group. Weights of fetal liver and kidney tissues were also significantly increased in S group. Histology assay indicated that there was no significant difference in the number of primary hair follicles between the two groups. However, the number of secondary hair follicles and the secondary to primary follicle (S/P) ratio was significantly higher in S group than those in C group, indicating that the Nano-Se supplement could promote the development of secondary follicles. Our results demonstrate that maternal supplement of Nano-Se could influence antioxidant status in the fetal skin, the resulted low ROS could up-regulate IGF-1 and IGF-1R, which improve the fetal hair follicle development and promote the growth development of fetal. Results of present study suggest that maternal dietary supplements of Nano-Se during gestation could be used to improve the hair follicle development and promote growth development in Cashmere goat fetus.

Dynamic Signals for Hair Follicle Development and Regeneration

Hair follicles form during embryonic development and, after birth, undergo recurrent cycling of growth, regression, and relative quiescence. As a functional mini-organ, the hair follicle develops in an environment with dynamic and alternating changes of diverse molecular signals. Over the past decades, genetically engineered mouse models have been used to study hair follicle morphogenesis and significant advances have been made toward the identification of key signaling pathways and the regulatory genes involved. In contrast, much less is understood in signals regulating hair follicle regeneration. Like hair follicle development, hair follicle regeneration probably relies on populations of stem cells that undergo a highly coordinated and stepwise program of differentiation to produce the completed structure. Here, we review recent advances in the understanding of the molecular signals underlying hair follicle morphogenesis and regeneration, with a focus on the initiation of the primary hair follicle structure placode. Knowledge about hair follicle morphogenesis may help develop novel therapeutic strategies to enhance cutaneous regeneration and improve wound healing.

Identification of cannabinoid type 1 receptor in dog hair follicles

In veterinary medicine, there is an increasing interest in the study of the endo-cannabinoid system and the possible use of the cannabinoids for the treatment of several diseases. Cannabinoid receptors (CB) are widely distributed in human and laboratory animal tissues, justifying the involvement of the endo-cannabinoid system in a great number of metabolic ways. Since there are no data regarding cannabinoid receptors in hair follicles of domestic animals, we investigated the presence and localization of CB1 receptor in dog hair follicles. By using a goat anti-CB1 polyclonal antibody, we observed CB1 receptor in the proximal part of both primary and secondary hair follicles. Staining was localized in the inner root sheath cells. We suppose that the endo-cannabinoid system is involved in the molecular mechanisms regulating hair follicle activity in dog. The identification of CB1 receptor at the level of the inner root sheath may help in the understanding of hair follicle biology and the possibility that cannabinoid molecules could be considered as suitable therapeutic tools in dog.

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.

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.

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

Reciprocal Requirements for EDA/EDAR/NF-κB and Wnt/β-Catenin Signaling Pathways in Hair Follicle Induction

Wnt/beta-catenin and NF-kappaB signaling mechanisms provide central controls in development and disease, but how these pathways intersect is unclear. Using hair follicle induction as a model system, we show that patterning of dermal Wnt/beta-catenin signaling requires epithelial beta-catenin activity. We find that Wnt/beta-catenin signaling is absolutely required for NF-kappaB activation, and that Edar is a direct Wnt target gene. Wnt/beta-catenin signaling is initially activated independently of EDA/EDAR/NF-kappaB activity in primary hair follicle primordia. However, Eda/Edar/NF-kappaB signaling is required to refine the pattern of Wnt/beta-catenin activity, and to maintain this activity at later stages of placode development. We show that maintenance of localized expression of Wnt10b and Wnt10a requires NF-kappaB signaling, providing a molecular explanation for the latter observation, and identify Wnt10b as a direct NF-kappaB target. These data reveal a complex interplay and interdependence of Wnt/beta-catenin and EDA/EDAR/NF-kappaB signaling pathways in initiation and maintenance of primary hair follicle placodes.

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.

Immunohistochemical evaluation of intermediate filament nestin in dog hair follicles.

Hair follicles (HFs) are self-renewing structures that reconstitute themselves through the hair cycle. They maintain reservoirs of stem cells (SC) that are thought to reside in the bulge area, a region localized in the lowermost permanent portion of HFs. In mice and humans, HF bulge cells express nestin and present stem features as pluripotency. Nestin is a class VI intermediate filament protein; it was first described as a specific marker of CNS stem cells, but recent studies suggest that it may represent a more general stem cell marker (Wiese et al., 2004; Hoffman, 2006). Bulge cell characteristics have mainly been studied in mice and humans, but recently, a bulge-like region was identified also in dog HFs (Pascucci et al., 2006). In this work we investigate the presence and localization of nestin in dog HFs with the aim of evaluating its expression and to correlate it with the location of the bulge-like region. Immunostaining of skin samples collected from healthy dogs was performed by using a rabbit anti-nestin polyclonal antibody. The presence of a population of immunoreactive cells was revealed in the hair follicle middle region, at the arrector pili muscle insertion level. An immunohistochemical signal was detected only in primary hair follicles throughout the hair cycle. These observations led us to conclude that nestin positive cells are located in the bulge-like region of dog HFs and strengthen our hypothesis regarding the correlation between this region and the dog HF stem compartment.

Edar and Troy signalling pathways act redundantly to regulate initiation of hair follicle development

The development of ectodermal organs requires signalling by ectodysplasin (Eda), a tumor necrosis factor (TNF) family member, its receptor Edar and downstream activation of the nuclear factor kappaB (NF-kappaB) transcription factor. In humans, mutations in the Eda pathway components cause hypohidrotic ectodermal dysplasia, a syndrome characterized by missing teeth, sparse hair and defects in sweat glands. It has been postulated that Eda acts redundantly with another TNF pathway to regulate ectodermal organogenesis. A potential candidate is Troy (or TNFRSF19 or Taj), a TNF receptor which is homologous with Edar in its ligand-binding domain, and is expressed in an overlapping pattern. We have characterized Troy null mice and crossed them with Eda-deficient mice. Single Troy mutants had no defects in ectodermal organs. Analysis of the double mutants revealed an essential role for Troy in hair follicle development. In mice, hair follicles develop in three different waves. Only primary hair follicles are missing in Eda single mutants, whereas the compound mutants lacked also the follicles of the second wave, as well as all hair follicles in the middle of crown leading to focal alopecia. Assessment of NF-kappaB activity with a transgenic reporter construct indicated that Eda is the main activator of NF-kappaB signalling in developing skin appendages and surprisingly that the functional overlap of Troy and Eda signalling pathways is mediated by NF-kappaB independent pathways.

Effects of field bean (Vicia fabaL. var.minor) dietary supplementation on plasma thyroid hormones, insulin, insulin-like growth factor-1 concentrations and mohair characteristics in growing Angora goat kids

Twenty-two Angora kids were used to study the effect of a dietary supplementation with field bean (Vicia faba L. var. minor) on hair follicle activity, mohair characteristics and plasma total thyroxine (T4), triiodothyronine (T3), insulin (INS) and insulin-like growth factor-1 (IGF-1) concentrations. At birth, their mothers were divided in two groups (S: supplemented, C: control), the S group being supplemented with 300 g/head/day of whole field bean. At weaning, diet of kids from S group was supplemented with 80 g/head/day of whole field bean. At weaning, secondary hair follicle activity (S: 0.91 ± 0.01, C: 0.84 ± 0.02, p < 0.01) and staple length (S: 5.82 ± 0.13 cm, C: 5.16 ± 0.14 cm, p < 0.001) were greater in the S group. At 155 days of age, secondary fibre diameter (S: 16.54 ± 0.35 μm, C: 18.09 ± 0.31 μm, p < 0.01) was higher in the C kids. Concentrations of total plasma T4 and T3 were higher (p < 0.001) in S (120 ± 12 and 4.87 ± 0.92 ng/ml respectively) than in C kids (92 ± 8 and 2.97 ± 0.77 ng/ml respectively). At weaning, T4 values were negatively correlated (p < 0.05) with the secondary fibre diameter and the T3/T4 ratio was positively correlated (p < 0.05) with the secondary to primary hair follicle ratio. At 155 days of age, both T3 and T3/T4 values were positively correlated (p < 0.01) with staple length. Plasma INS (0.11 ± 0.03 ng/ml) and total IGF-1 concentrations (232 ± 13 ng/ml) were not affected by diet. Improvements of diet quality in kids positively affected fibre diameter and length and follicle activity rate. We suggest that increased circulating thyroid hormones concentrations, but not those of INS and IGF-1, may contribute to the beneficial actions of nutritional supplementation on anatomical growth and mohair production of kids.

Demonstration of β-glucan receptors in the skin of aquatic mammals—a preliminary report

Using immunohistochemistry, the study clearly demonstrates three important β-glucan receptors (Ficolin/P35, MBL, Dectin-1; members of the lectin-complement pathway of innate immunity) in the integument of six marine and freshwater aquatic mammals (Northern fur seal, Common seal, Walrus, Coypu, Capybara, Otter), but only weakly in two dolphin species. Most of the non-dolphin mammals exhibited strong reactions, especially with regard to the skin glands (tubular apocrine glands, sebaceous glands), for L-Ficolin/P35 and MBL. Distinct reaction staining could also be observed in the epidermis and the outer epithelial sheath of primary hair follicles.

The Wnt inhibitor, Dickkopf 4, is induced by canonical Wnt signaling during ectodermal appendage morphogenesis

Ectodermal appendage morphogenesis requires continuous epithelial–mesenchymal cross-talk during development. Canonical Wnt signaling has been shown to be pivotal during this process and its inhibition leads to the absence of any morphological or molecular signs of appendage formation, including hair follicles (HFs). In the mouse, primary HFs arise in utero starting just before E14.5, when the first morphological signs of a placode are discernible. In this study, our goal was to identify novel factors expressed during primary HF morphogenesis. We performed transcriptional profiling of the developing epidermis at 12 h intervals between E12.5 and E15.5. One of the significantly differentially expressed genes was the Wnt inhibitor Dickkopf 4, Dkk4. We show that Dkk4 mRNA increases sharply in the dorso-lateral epidermis around E14 and then decreases until E15.5. Using whole mount in situ hybridization, we show that Dkk4 mRNA is localized to the pre-placodes at sites of presumptive epithelial–mesenchymal interactions during appendage morphogenesis, including the dental lamina, mammary gland, eccrine gland, and primary and secondary HFs. In silico analysis, reporter gene assays as well as in vitro transfections of LEF1 and β-catenin show that Dkk4 is a potential downstream target of canonical Wnt signaling. In addition, we demonstrate a direct physical interaction between LEF1/β-catenin complex and the Dkk4 promoter using ChIP. We propose that Dkk4 acts in a negative feedback loop to attenuate canonical Wnt signaling, and may facilitate a switch to the non-canonical Wnt planar cell polarity (PCP) pathway that is involved in cell movements during morphogenesis.

Generation of the primary hair follicle pattern

Hair follicles are spaced apart from one another at regular intervals through the skin. Although follicles are predominantly epidermal structures, classical tissue recombination experiments indicated that the underlying dermis defines their location during development. Although many molecules involved in hair follicle formation have been identified, the molecular interactions that determine the emergent property of pattern formation have remained elusive. We have used embryonic skin cultures to dissect signaling responses and patterning outcomes as the skin spatially organizes itself. We find that ectodysplasin receptor (Edar)-bone morphogenetic protein (BMP) signaling and transcriptional interactions are central to generation of the primary hair follicle pattern, with restriction of responsiveness, rather than localization of an inducing ligand, being the key driver in this process. The crux of this patterning mechanism is rapid Edar-positive feedback in the epidermis coupled with induction of dermal BMP4/7. The BMPs in turn repress epidermal Edar and hence follicle fate. Edar activation also induces connective tissue growth factor, an inhibitor of BMP signaling, allowing BMP action only at a distance from their site of synthesis. Consistent with this model, transgenic hyperactivation of Edar signaling leads to widespread overproduction of hair follicles. This Edar-BMP activation-inhibition mechanism appears to operate alongside a labile prepattern, suggesting that Edar-mediated stabilization of beta-catenin active foci is a key event in determining definitive follicle locations.

NF-κB transmits Eda A1/EdaR signalling to activate Shh and cyclin D1 expression, and controls post-initiation hair placode down growth

A novel function of NF-kappaB in the development of most ectodermal appendages, including two types of murine pelage hair follicles, was detected in a mouse model with suppressed NF-kappaB activity (c(IkappaBalphaDeltaN)). However, the developmental processes regulated by NF-kappaB in hair follicles has remained unknown. Furthermore, the similarity between the phenotypes of c(IkappaBADeltaN) mice and mice deficient in Eda A1 (tabby) or its receptor EdaR (downless) raised the issue of whether in vivo NF-kappaB regulates or is regulated by these novel TNF family members. We now demonstrate that epidermal NF-kappaB activity is first observed in placodes of primary guard hair follicles at day E14.5, and that in vivo NF-kappaB signalling is activated downstream of Eda A1 and EdaR. Importantly, ectopic signals which activate NF-kappaB can also stimulate guard hair placode formation, suggesting a crucial role for NF-kappaB in placode development. In downless and c(IkappaBalphaDeltaN) mice, placodes start to develop, but rapidly abort in the absence of EdaR/NF-kappaB signalling. We show that NF-kappaB activation is essential for induction of Shh and cyclin D1 expression and subsequent placode down growth. However, cyclin D1 induction appears to be indirectly regulated by NF-kappaB, probably via Shh and Wnt. The strongly decreased number of hair follicles observed in c(IkappaBalphaDeltaN) mice compared with tabby mice, indicates that additional signals, such as TROY, must regulate NF-kappaB activity in specific hair follicle subtypes.

Forschungsaktivitäten und Innovationen in der Haarpflege - zukünftige Perspektiven in der Haarforschung

The activities in the segment of hair research essentially concentrate on four ranges: i) hair morphogenesis, ii) hair growth and hair loss, iii) hair shape as well as iv) hair colour and hair greying. While doing so, we try to identify the different regulating molecular mechanisms, which underlie the different phases of hair follicle gro wth for the purpose of focused interventions on these processes. Indeed, we understand until today numerous signals, which play a role in the primary hair follicle development. But how this know ledge will help us to influence the transformation period from the telogen to the anagen, is not yet clear. Another research priority lies in the localisation of the stem cells, which are essential for the cyclic regeneration of the hair follicle. Ubersicht

Multiple Roles for Elastic Fibers in the Skin

Dermal elastic fibers are believed to have a primary role in providing elastic stretch and recoil to the skin. Here we compare the structural arrangement of dermal elastic fibers of chick skin and different animal species. Most elastic fibers in chick skin are derived from cells that line the feather follicle and/or smooth muscle that connects the pterial and apterial muscle bundles to feather follicles. Elastic fibers in the dermis of animals with single, primary hair follicles are derived from cells lining the hair follicle or from the ends of the pili muscle, which anchors the muscle to the matrix or to the hair follicle. Each follicle is interconnected with elastic fibers. Follicles of animals with primary and secondary (wool) hair follicles are also interconnected by elastic fibers, yet only the elastic fibers derived from the primary follicle are connected to each primary follicle. Only the primary hair follicles are connected to the pili muscle. Human skin, but not the skin of other primates, is significantly different from other animals with respect to elastic fiber organization and probably cell of origin. The data suggest that the primary role for elastic fibers in animals, with the possible exception of humans, is movement and/or placement of feathers or hair.

Bone Morphogenetic Protein Signaling Regulates Postnatal Hair Follicle Differentiation and Cycling

Hair follicle morphogenesis and cycling were examined in transgenic mice that overexpress the bone morphogenetic protein (BMP) inhibitor Noggin under the control of the neuron-specific enolase promoter. The Noggin transgene was misexpressed in the proximal portion of the hair follicle, primarily the matrix cells, apart from the usual expression in neurons. Transgene expression appeared only after induction of both the primary (tylotrich) and secondary (nontylotrich) pelage hair follicles had already occurred, thus allowing examination of the role of BMP signaling in follicles that had been induced normally in the presence of BMPs. The overexpression of Noggin in these animals resulted in a dramatic loss of hair postnatally. There was an apparently normal, but shortened period of postnatal hair follicle morphogenesis, followed by premature initiation of hair follicle cycling via entry into the first catagen transformation. This resulted in a complete loss of hair shafts from the nontylotrich hair follicles in these mice while the tylotrich hair follicles were normal. The onset of anagen of the first postnatal hair follicle cycle was also accelerated in the transgenic mice. Our results show that BMP signaling is specifically required for proper proliferation and differentiation during late morphogenesis of nontylotrich hair follicles and that inhibition of this signaling pathway may be one of the triggers for the onset of catagen when the follicles are in anagen and the onset of anagen when the follicles are in telogen. Ectopic sebocyte differentiation was another hallmark of the phenotype of these transgenic mice suggesting that BMP signaling may be an important determinant of lineage selection by common progenitor cells in the skin. BMPs likely promote a hair follicle-type differentiation pathway of keratinocytes while suppressing the sebaceous differentiation pathway of skin epithelium.

Effect of testosterone and oestradiol-17beta on canine hair follicle culture.

Skin biopsies were taken from four body sites (head, thorax, flank and perineum) of three male entire Beagles and the primary hair follicles were isolated. Culture conditions were established to keep the hair follicles growing for up to 7 days. Additionally, hair follicles were incubated in supplemented medium (containing insulin, transferrin, glutamine and sodium selenite) with or without the addition of testosterone (T) (1, 10 or 100 ng/ml) or oestradiol-17beta (E2beta) (0.01, 0.1 or 1 ng/ml), respectively and the daily growth of hair follicles was measured. In vitro daily growth of hair follicles from the thorax was stimulated by the low concentration of both hormones, but the growth of those from the flank was inhibited by the high concentration of both hormones. Hair follicles from the head were positively influenced by the lowest concentration of T and the medium concentration of E2beta. The daily growth of hair follicles from the perineum was not significantly influenced by either hormone.