Changes in the number of Merkel cells with hair cycle in discs in the back of rats

2003 Fiscal Year Final Research Report Summary

• Project/Area Number: 14570811
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Dermatology
• Research Institution: Saga University
• Principal Investigator: NARISAWA Yutaka Saga University, Medical School, Professor, 医学部, 教授 (60164498)
• Co-Investigator(Kenkyū-buntansha): MIURA Yoshihiro Saga University, Medical School, Assistant, 医学部, 助手 (20304892) ; NAKAFUSA Jyunji Saga University, Medical School, Assistant, 医学部, 助手 (50253828) ; MISAGO Noriyuki Saga University, Medical School, Assistant, 医学部, 講師 (90199977) ; SUZUKI Yasuyuki Saga University, Medical School, Assistant, 医学部, 助手 (20363434) ; HIRASHIMA Noriyuki Saga University, Medical School, Assistant, 医学部, 助手 (30346879)
• Project Period (FY): 2002 – 2003
• Keywords: Merkel cell / hair follicle / hair disc / hair cycle

Research Abstract

There are many unclear propblems in the embryological origin, differentiation and function of Merkel cells. The hair disc is an important research target of functional analysis of Merkel cells because relatively many Merkel cells are present in hair discs. It has been well known that hair follicle, as well as many Merkel cells, are also important elements constituting hair discs.
Hair follicles undergo a unique cyclic change. Mechanism of anagen, catagen, and telogen in the hair, cycle in hair follicles has not been elucidated. Interestingly, it has been reported that the population of Merkel cells in hair discs were related to the hair cycle in mice. In this study, we present an obvious evidence of the hair cycle dependency of Merkel cell population in hair discs of normal mice and rat skin.
Hair was depilated from the back in mice, and epidermal sheets were prepared on days 0,1,3,5,8,12,17, and 18 after depilation to investigate changes in the number of Merkel cells with the hair cycle in three dimensions. The number of Merkel cells changed with the hair cycle.
Next, we three-dimensionally observed time-course changes in the number of Merkel cells in hair discs starting in the embryonic period. Using rat back skin, changes in the number of Merkel cells during the morphogenesis of hair discs and later hair cycle were investigated. Epidermal sheets of rat back skin were prepared fom the 18th embryonic day till day 100 after birth. During the first hair cycle, which is the developmental step of hair follicle morphogenesis, and the second and third cycles, which are regeneration of the hair follicles, Merkel cells in hair discs increased during the early, to middle phase of anagen and decreased during the middle phase of anagen to catagen and telogen in embryos and after birth. These three-dimensional findings clearly demonstrated that the Merkel cell distribution in hair discs changes with the hair cycle.
Moreover, morphological variation of Merkel cells, oval and dendritic cell types, at the light microscopic level has been reported. The time-course frequencies of the two types were three-dimensionally investigated, respectively. The number of "oval cell type. Merkel cells was 5.6 per hair disc, being not markedly affected by the hair cycle. In contrast, the number of dendritic cell type Merkel cells markedly changed with the hair cycle, This difference between oval and dendritic cell type Merkel cells may suggest some functional differences of two types such as some kinds of secretory function related to the hair cycle.