Abstract
The skin carries a number of appendages, including hair follicles and a range of glands, which develop under the influence of EDAR signalling. A gain of function allele of EDAR is found at high frequency in human populations of East Asia, with genetic evidence suggesting recent positive selection at this locus. The derived EDAR allele, estimated to have reached fixation more than 10,000 years ago, causes thickening of hair fibres, but the full spectrum of phenotypic changes induced by this allele is unknown. We have examined the changes in glandular structure caused by elevation of Edar signalling in a transgenic mouse model. We find that sebaceous and Meibomian glands are enlarged and that salivary and mammary glands are more elaborately branched with increased Edar activity, while the morphology of eccrine sweat and tracheal submucosal glands appears to be unaffected. Similar changes to gland sizes and structures may occur in human populations carrying the derived East Asian EDAR allele. As this allele attained high frequency in an environment that was notably cold and dry, increased glandular secretions could represent a trait that was positively selected to achieve increased lubrication and reduced evaporation from exposed facial structures and upper airways.
Highlights
The skin acts as a barrier to the immediate environment, relying in particular on its outermost layer of dead cells to protect the body from desiccation and infection
The sebaceous glands are associated with hair follicles and secrete sebum composed of a complex combination of lipids [25]
Measurement of gland sizes on tissue sections showed that the sebaceous glands associated with each hair follicle are larger in transgenic than in wild type animals (Figure 1D)
Summary
The skin acts as a barrier to the immediate environment, relying in particular on its outermost layer of dead cells to protect the body from desiccation and infection. Living tissues require some direct contact with the environment for exchange of nutrients, water and air. These external contacts are facilitated by a battery of glands that produce a diverse array of secretions and carry out very diverse functions. In addition to maintaining tissue moisture, many glandular secretions act as a barrier to infection [1]. The basic structure of a gland consists of an epithelial sheet, which contains the cells responsible for producing and secreting the glandular product, and a supporting connective tissue carrying blood vessels. Glands that are required to secrete large volumes into a limited number of ducts or in a short space of time (e.g. saliva, milk, tears) are more complex, having a branched epithelium to increase the amount of secreting epithelial surface within a given volume of tissue [1]
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