Biomedical Engineering Reference
In-Depth Information
Fig. 4
Structure of hair follicle. h
e bulge region of the hair follicle is the niche of HFSCs. h
e
HFSCs generate transient-amplifying cells that contribute to the formation of the hair follicle.
cells. h e HFSCs, however, lack unique markers to distinguish them from their
transient-amplifying progeny, similar to other stem cells. Accordingly, it is still
dii cult to obtain a pure population of HFSCs. h e high expression of integrin on
HFSCs suggests that strong adherence to the basement membrane is required for
them to localize in the niche and maintain their stemness. Tumbar
et al.
(2004)
reported that a purii ed HFSC population showed positive staining of integrin
β1, integrin β4 and integrin α6, although their expression was not constant and
l uctuated by hair cycle. Very recently, Kloepper
et al.
(2008) demonstrated that
immunohistochemical staining did not show signii cant dif erence in the expression
of integrin β1 between the bulge region and other parts of the outer root sheath.
More work is required to clarify the contribution of integrin molecules to the hair
follicle niche.
It has been demonstrated that CD34 expression co-localized with slow-
cycling and keratin 15-positive cells in the bulge region on the mouse hair follicle
(Trempus
et al.
2003). h ese researchers sorted CD34 and integrin α6-double
positive cells, and these cells were predominantly in the G
0
/G
1
phase and showed
a high proliferative potential
in vitro
. In contrast, CD34-negative cells were in the
G
2
/M and S phase, and the expression of integrin α6 was low. h ese results indicate
that CD34 can be used as a specii c marker for the HFSCs. In contrast, there are
several reports showing that CD34-negative cells had stem cell properties. Such
conl icting results must be clarii ed by extensive studies.
