Biology of the wool follicle: an excursion into a unique tissue interaction system waiting to be re‐discovered

Thyroidectomy surgery performed late in gestation results in perturbations in wool follicle development in foetal sheep, showing the importance of thyroid hormones for wool follicle development. The aim of this study was to determine the influence of transient manipulation of thyroid hormone status at a time corresponding with foetal primary wool follicle initiation. Pregnant Merino ewes (n 5 12 per treatment) were treated daily between gestational days 55 and 64 with control (vehicle), exogenous thyroxine (T4) or propylthiouracil (PTU), an inhibitor of T4 synthesis, and conversion to the active form of the thyroid hormone (triiodothyronine). There were no significant differences in birth weight, gestational lengths and birth coat scores of the resultant lambs. The total primary and secondary follicle densities were significantly lower in lambs exposed to exogenous T4 compared with other treatments (P , 0.05). However, the T4 group displayed a higher proportion of mature secondary follicles (reflected by increased mature secondary follicle densities and mature secondary/primary follicle ratios) than the other treatment groups (P , 0.05). The skin morphology of the lambs differed 12 months later, with the T4 group having significantly higher total follicle densities compared with the PTU group, largely attributed to increased mature and total secondary follicle densities. However, this increase in wool follicle densities did not translate to differences in the fleece yields and weight, fibre diameter, staple lengths or any other fibre parameters. This study showed that transient manipulation of thyroid hormone status during foetal primary follicle initiation does have long-term consequences on the morphology of wool follicles, in particular the maturity of secondary wool follicles.

Section: Introductionmentioning

confidence: 97%

The effects of short-term manipulation of thyroid hormone status coinciding with primary wool follicle development on fleece characteristics in Merino sheep

McDowall

Edwards

Hynd

2011

“…These follicles are located in skin and have properties in common with other components of the mammalian integument (outermost layers of tissue of the body). The current background to research on hair follicles -E-mail: h.galbraith@abdn.ac.uk in commercial animal species indicates limited funding and associated activity in Europe and elsewhere including Australia (Rogers, 2006). This is despite evidence of some diversification of study on the science of integumental tissues of farm animals into areas such as foot lameness biology in cattle (Galbraith and Scaife, 2008).…”

Section: Introductionmentioning

confidence: 97%

“…Response of isolated mohair follicles to EGF EGF is one of a number of signalling molecules which are known to affect growth of fibre in sheep and has been used as a systemic treatment to assist in harvesting of wool (Rogers, 2006). Such a treatment using mouse-derived EGF was tested at two concentrations in mohair follicles (Table 3) (Figure 3a and b) and (ii) increased incidence of club hair formation (Figure 4).…”

Section: Collection and Preparation Of Hair Folliclesmentioning

confidence: 99%

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

Galbraith

2010

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.Keywords: hair follicle, in vitro culture, cashmere, mohair, sheep wool ImplicationsHair fibres are products with value depending on quality and quantity produced. We require information to optimise breeding and husbandry of fibre-producing animals. This includes better understanding of the hair follicles in skin, which produce fibre. This report reviews results from in vitro studies on follicles removed from skin of sheep and goats. It describes how: (i) var...

“…The development of primary, secondary and derived follicles in the pelage of Merino sheep has been described by Rogers (2006). Primary follicles with arrector pilae muscle, Although induction of all follicles and maturity of primaries is considered to be complete by birth at E145 to 150, growth of hair by secondaries continues to develop for a further 4 to 5 months.…”

Section: General Properties Of Integumental Tissuesmentioning

confidence: 99%

“…Changes in intracellular volume of fibroblasts and composition of the extracellular matrix of the DP occur concomitant with changes in physiological state of the hair follicle. New anagen involves proliferation and movement of stem cells from the bulge area (located below the sebaceous gland) in the mouse or from ORS in the sheep (Rogers, 2006) to form a new matrix of progenitor cells which surround the dermal papilla. These cells then proliferate and differentiate according to anatomical position to form the hair shaft, medulla, if present, and other concentric epithelial layers of the renewing follicle.…”

Section: General Properties Of Integumental Tissuesmentioning

confidence: 99%

Fundamental hair follicle biology and fine fibre production in animals

Galbraith

2010

Hair 'fine' fibre is an important commercial product of farmed and certain wild animal species. The fibre is produced in follicles embedded in skin. These have properties in common with other tissues of the integument and have importance in determining yield and quality of fibre. Means of understanding and improving these characteristics are informed by knowledge of integumental and follicle biology. This paper reviews contemporary information that identifies the major fibre-producing species and their production characteristic. It surveys knowledge describing fundamental biology of the integument and considers information derived for the hair follicle from studies on a number of species including genetically modified mice. It identifies the composition of the follicle and describes components and interrelationships between epidermal hair-fibre producing epidermis and fibroblastand connective tissue-containing dermis. The structure of different primary and secondary follicle types, and associated structures, are described. Focus is given to the alterations in anatomy and in behaviour from active to inactive state, which occurs during the hair follicle cycle. Information is provided on the anatomical substructures (hair medulla, cortex, cuticles and supporting sheaths and dermal papilla), cellular and extracellular composition, and adhesion and chemical signalling systems, which regulate development from the early embryo to post-natal state and subsequent cycling. Such signalling involves the dermis and its specialist fibroblasts, which secrete signalling molecules, which along with those from local epidermis and systemic sources, largely determine structure and function of epidermal cells. Such chemical signalling typically includes endocrine-, paracrine-, autocrine-and juxtacrine-acting molecules and interactions with their receptors located on cell membranes or intracellularly with transduction of message mediated by transcription factors at gene level. Important hormones and growth factors and inhibitors regulating morphogenic and/or mitogenic activity are identified. These mediate mechanisms associated with presence or absence in skin and development of patterning for primary or secondary follicles. Reference is made to deposition of individual keratins and keratin-associated proteins in follicle sub-structures and to fibre properties such as length, diameter, medullation, crimp and lustre. Pre-and post-natal regulation of pigmentation by melanocytes is reviewed. Brief attention is given to genomic and non-genomic variation and impact on the phenotypes expressed and the role of regulatory gene products as potential molecular markers for selection of superior animals. The importance of nutrients in providing substrates for follicular structures and enzymes and in molecules facilitating gene expression is also considered.