1. Changes in Different Melanocyte Populations During Hair Follicle Involution (Catagen) 
Andreya Sharov, Desmond J. Tobin, Tatyana Y. Sharova, Ruzanna Atoyan, Vladimir A. Botchkarev 
Journal of Investigative Dermatology 
Volume 125, Issue 6, Pages (December 2005)
DOI: /j X x
Copyright © 2005 The Society for Investigative Dermatology, Inc Terms and Conditions

2. Figure 1
Dynamic changes in the hair follicle pigmentary unit during catagen. The hair cycle was induced in the back skin of 8-wk-old tyrosine-related protein 2 (Trp2)–LacZ mice by depilation. Skin was harvested at the different time points on days 14–22 after depilation. Cryostat sections (8-μm thickness) of the back skin of postnatal Trp2–LacZ mice at defined stages of catagen were processed for X-gal staining. (A, B) Anagen VI. Trp2-positive melanocytes are visible in the interfollicular epidermis (small arrowhead), dermis (large arrowhead), the bulge area of the HF (small arrow), outer root sheath (medium arrows), and in the precortex area above the follicular papilla (A, B, large arrows). (C, D) Catagen I–II. Subset of the pre-cortex melanocytes (large arrows) is seen in the follicular papilla (small arrows). (E, F) Catagen IV–VI. Melanocytes are seen in the dermis (arrowheads), the outer root sheath (small arrows), follicular papilla (medium arrow), and the pre-cortex area (large arrow). (G–J) Serial high-resolution light microscopic images were obtained from the catagen hair follicles of C57BL/6 mice. Melanocyte-like cells are seen in the follicular papilla (FP) (arrows) of late catagen HF. (K) Catagen VIII. Melanocytes are seen in the epidermis (small arrowhead), dermis (large arrowheads), the bulge (small arrow), secondary hair germ (medium arrow), and follicular papilla (large arrow). (L) Histomorphometry of the epidermal and dermal melanocytes shows significant increase in number of the melanocytes located in the intrafollicular dermis during catagen, compared to the late anagen (mean+SEM, p<0.05, Student's t test).In (I–K), insets show a high magnification of the labeled areas. Scale bars=100 μm.
Journal of Investigative Dermatology  , DOI: ( /j X x)
Copyright © 2005 The Society for Investigative Dermatology, Inc Terms and Conditions

3. Figure 2
Expression of the Fas receptor, TUNEL, c-kit, and Bcl-2 in subpopulations of the hair follicle melanocytes during catagen. The back skin cryosections of tyrosine-related protein 2 (Trp2)–LacZ transgenic mice at distinct stages of catagen were processed for the double immuno-visualization of β-galactosidase (β-gal) and TUNEL (A–C), CD95/Fas receptor (D, E), c-kit (F–I), Bcl-2 (J–L), and Ki-67 (M). Nuclei are counterstained by DAPI. (A) Catagen II. Colocalization of β-gal and TUNEL (yellow fluorescence) in the hair bulb melanocytes located close to the hair shaft (large arrows). Single TUNEL positive keratinocytes are seen in the hair matrix (small arrows). (B) Catagen VI. Disappearance of TUNEL-positive melanocytes from the regressing hair shaft. Melanocytes located close to the follicular papilla (large arrow) are TUNEL-negative. TUNEL-positive cells are also visible in the epithelial strand (small arrows). (C) Telogen. Lack of co-localization of TUNEL (small arrow) and β-gal (large arrows) in the secondary hair germ. (D) Catagen II. Expression of the Fas-receptor (red or yellow fluorescence, large arrows) on melanocytes located close to the hair shaft, as well as in the inner root sheath (small arrowhead) and in the hair shaft (large arrowhead). Melanocytes located close to the follicular papilla do not show Fas expression (green fluorescence, small arrows). (E) Catagen VI. Disappearance of Fas-positive melanocytes from the regressing hair shaft in catagen VI HF. Melanocytes located closely to the follicular papilla (small arrows) are Fas-negative. Fas-positive keratinocytes are visible in the regressing hair shaft (large arrows). (F) Catagen II. Trp2 positive melanocytes are visible in the follicular papilla (small arrows). Strong c-kit expression is seen in the hair matrix keratinocytes (large arrows). Inset shows a high magnification of the labeled area. (G) Catagen III–IV. c-kit expression in some melanocyte localized in the follicular papilla (yellow fluorescence, small arrow) and in the hair matrix keratinocytes (red fluorescence, large arrow). (H) Catagen V. c-kit expression in the melanocytes localized in the connective tissue sheath around the follicular papilla (green/yellow fluorescence, arrow). (I) Catagen VI. Decrease of c-kit expression in the melanocytes localized in the follicular papilla (green fluorescence, arrow). (J) Catagen II. Bcl-2 expression in the follicular papilla fibroblasts (red fluorescence, large arrow) and melanocytes located in the follicular papilla (yellow fluorescence, small arrow). Melanocytes located above the follicular papilla are Bcl-2 negative (green fluorescence, arrowhead). (K) Catagen IV. Some of the melanocytes located in the regressing outer root sheath express Bcl-2 (red/yellow fluorescence, large arrows), whereas the others are Bcl-2 negative (green fluorescence, small arrows). (L) Catagen VII. Two melanocytes located in the secondary hair germ close to the follicular papilla express Bcl-2 (red/yellow fluorescence, large arrows), whereas the melanocyte located far above the follicular papilla is Bcl-2 negative (green fluorescence, small arrow). (M) Ki-67 expression is seen in the epidermis, sebaceous glands (arrowheads), as well as in single cells of the secondary hair germ (large arrows), whereas follicular melanocytes remain Ki-67 negative (small arrow). Inset shows high magnification of the labeled area. Abbreviations: CH, club hair; FP, follicular papilla; ES, epithelial strand; SHG, secondary hair germ. Scale bar=50 μm.
Journal of Investigative Dermatology  , DOI: ( /j X x)
Copyright © 2005 The Society for Investigative Dermatology, Inc Terms and Conditions

4. Figure 3
Model illustrating changes in distinct subpopulations of the hair follicle (HF) melanocytes during catagen. Melanocyte subpopulations of the HF are heterogeneous in their dynamics during catagen. Melanocytes located in the outer root sheath express Bcl-2, are TUNEL-negative, and most likely represent surviving cells. Pigment-producing melanocytes located above the follicular papilla become divided into two distinct subpopulations: one melanocyte subpopulation closely associated with the regressing hair shaft expresses Fas receptor and is likely to undergo apoptosis, whereas the second melanocyte subpopulation most likely migrates downward into the follicular papilla, shows the expression of the c-kit receptor and Bcl-2 and, subsequently, could be seen in the HF connective tissue sheath. During the subsequent hair cycle, restoration of the HF pigmentary unit occurs most likely from the melanocytes and melanocyte stem cells that survive catagen and are located in the secondary hair germ and in the bulge.
Journal of Investigative Dermatology  , DOI: ( /j X x)
Copyright © 2005 The Society for Investigative Dermatology, Inc Terms and Conditions