Studies On Skin And Hair Follicles Of The Chipmunks

The hair follicle is an appendage of the skin. It is composed of a dermal papilla, hair matrix, hair shaft, outer root sheath, inner root sheath and connective tissue sheath. Hair follicles can periodically regenerate, and a hair cycle is composed of anagen, catagen and telogen phases. We studied the hair cycle of wild chipmunks by shaving their fur and observing pigment changes in their skin. We also observed the affects of seasonal changes, shaving and other factors on the hair cycles. Changes in different growth stages of the skin and hair follicle were assessed by histological methods. Epithelial stem cells (EpSCs) and melanocyte stem cells (McSCs) were localized to the hair follicle bulge. We then compared molecular expression during the hair cycle and pigment synthesis using in situ hybridization to gain better understanding of regulatory mechanisms. The experimental results are as follows:(1) Chipmunks have six hair types:Vibrissae, Guard hair, Awl hair, Auchene hair, Zigzag hair and tail hair. Zigzag hairs are the most prevalent. The coloring of chipmunk tail hair is most unique, including white, black and alternating yellow and black from the tip to the hair root. The pigmentation of chipmunk dorsal hair follicles is organized into yellow and black stripes. The hair cycle has the following rule: immature chipmunks demonstrate synchronous growth over2-3cycles. After September, the cycle enters telogen and lasts until after hibernation, about six months when it enters a new growth cycle. During hibernation, depilation can induce re-entery to anagen. Similar to mice, regenerative hair waves become more complex in adult chipmunks. Histological sections reveal that during telogen, the skin became thinner, the hair follicle apoptosed and the number of hair follicles decreased, the epidermal surface appeared uneven.(2) During anagen, CD34and K15showed a strong positive signal in the bulge, a structure analogous to the mouse hair follicle bulge housing stem cells. Thus CD34and K15can be used as EpSC markers of hair follicles. BrdU label retention was also found in the same location. PCNA showed a strong positive signal in the epidermis, outer root sheath, hair matrix and hair medulla of hair follicles. Ki67also showed a positive signal in the bulge, the epidermis and hair matrix around the dermal papilla. CK14was detected in the epidermis and the outer root sheath. β-catenin is seen in the epidermis of the hair follicle, outer root sheath, inner root sheath and hair medulla. It was also found in the dermal papilla. (3) Exons encoding BMP2, BMP4, Noggin, Pax3, Mitf and Mc1R were amplifed by PCR from chipmunk genomic DNA. BMP2, BMP4, Noggin, Pax3, Mitf, Mc1R antisense RNA probes were also made. In situ hybridization showed a weakly positive BMP2and BMP4signal in the chipmunk anagen outer root sheath and hair medulla.(4) The chipmunk pelage was arranged with alternating yellow and black stripes, each containing a similar proportion of the6different hair types. Hairs present in the yellow stripes showed typical characteristics of Agouti hair, with a long band of pheomelanin below the black hair tips; a few of them lack black hair tips. In contrast, black stripes had no pheomelanin or only a short yellow stripe. Mart-1, TRP-1and DCT were expressed in the hair matrix of hair follicles in two stripes and pigment accumulated in the medullary layer of the hair shaft. DCT and Mart-1were also expressed in the bulge where hair follicle stem cells are localized, suggesting that McSCs and EpSCs may share a common niche or alternatively may be in close proximity. DCT and Mart-1could be used as markers for melanocyte stem cells in chipmunks.