Abstract:

BACKGROUND: There are many researches on the mouse skin morphology and development in embryonic period, but we have a poor understanding of the histomorphological evolution process of the skin and hair follicle after birth.
OBJECTIVE: To explore the morphological changes and rules of the newborn mouse skin and hair follicle development.
METHODS: The thickness of the back skin from the 1-12-day-old mice was analyzed using Image J software through conventional paraffin-embedded section and hematoxylin-eosin staining methods. The morphology of the hair follicle was observed under an optical microscope, and the number of hair follicles and vesicle-shaped structures were recorded. The development of hair follicles according to the developmental characteristics was divided into four periods, in comparison with Ralf Paus staging.
RESULTS AND CONCLUSION: On the early stage of hair follicle formation (1-4 days), the newborn mice appeared with thinnest skin [(405.36±26.60) μm in thickness] on the day of birth, and there was no adipose tissue in hypodermis and few hair bulbs in epidermis. On day 2, the skin was thickened to (927.11±27.25) μm, with more dermal fibroblasts, and the horny cells from the stratum basale migrated to forming hair papilla. On days 3-4, the skin was thinned to (738.60±82.07) μm, increasing hair follicles and expanded hair bulbs were observed, with the dermis covered by dermal sheath. On the middle stage of hair follicle formation (5-7 days), the skin was thickened again on day 5, and became thickest [(2 369.57±34.06) μm in thickness] on day 7, there were increased number of hair follicles, hair bulbs and vesicle-shaped structures, the internal dermal sheath was extended into the epidermis to form hair roots, the dermal sheath was differentiated into external root sheath, and the internal root sheath extended deeply to form a closed germinal matrix. On the later stage of hair follicle formation (8-9 days), the skin thickness was decreased to (1 743.37±75.05) μm on day 8 and (1 987.07 ±18.65) μm on day 9; the hair papilla was surrounded by hair matrix; hair canal and hair shaft gradually formed, and the growing internal root sheath extended into the deep layer, forming more hair roots. On the maturation sage of hair follicle (10-12 days), the skin was thickened to          (2 399.33±27.00) μm; the number of both hair follicles and vesicle-shaped structures was about 30; the hair shaft lengthened, reaching the muscle layer, which grew upward through the hair canal and further crossed the epidermis to form the hair that could be observed by the naked eye. These findings suggest that there is synchronical or non-synchronical correlation between the skin development and hair follicle formation at the neonatal mouse back, presenting with the ascendant curve. The development process of hair follicle is imbalanced and different, and staging of hair follicle formation is available for observing the differentiation progress of hair follicle.

中国组织工程研究杂志出版内容重点：组织构建；骨细胞；软骨细胞；细胞培养；成纤维细胞；血管内皮细胞；骨质疏松；组织工程

Key words: Mice, Skin, Hair Follicle, Histology, Tissue Engineering