Fundamental hair follicle biology and fine fibre production in animals

Abstract

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.

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

“…The in vitro approach coupled with histological, immunohistochemical and in situ hybridisation methodology may be applied to facilitate investigation of intrinsic morphology and hair shaft elongation in such follicles. Of particular interest will be the patterns of keratinocyte proliferation and differentiation and role of candidate regulatory molecules (Galbraith, 2010) in producing the recognised hair growth phenotypes.…”

“…The production of hair by follicles, which have epidermal and dermal constituents similar to other tissues of the integument, is a complex process. This has also been the subject of review in this symposium (Galbraith, 2010). It has parallels in fundamental regulatory mechanisms involving stem cells, and programmed cellular proliferation and differentiation, which occurs in typical development from conception to maturity of multicellular animals.…”

Genetics of fibre production and fleece characteristics in small ruminants, Angora rabbit and South American camelids

“…Except for the Extension locus located on chromosome 14 (Vage et al, 2003), other loci affecting colour patterns in sheep have yet to be identified. Further details on the biology of pigment production have been provided by Galbraith (2010). Several wool-keratin genes, which are often clustered in families, have been cloned in the last decades.…”

Relationships between integumental characteristics and thermoregulation in South American camelids

“…Hair fibre, synthesised from follicles located on the external integumental surface of the body (Galbraith, 2010a), is commonly regarded as a unique mammalian feature. It is assumed that mammalian hair evolved about 200 million years ago (Ruben, 1995;Meng and Wyss, 1997;Grigg et al, 2004).…”

“…goats, camels, South American camelids (SACs) and yak). The artificial selection resulted in marked changes with regard to follicle number, type, distribution, growth and even natural shedding (Allain and Renieri, 2010;Antonini, 2010;Galbraith, 2010a). The impact of these genetic manipulations on the adaptation and acclimatisation of the animals is not completely understood.…”