Keratinocytes Play a Role in Regulating Distribution Patterns of Recipient Melanosomes In Vitro

Melanosomes in keratinocytes of Black skin are larger and distributed individually whereas those within keratinocytes of Caucasian skin are smaller and distributed in clusters. This disparity contributes to differences in skin pigmentation and photoprotection, but the control of these innate distribution patterns is poorly understood. To investigate this process, cocultures were established using melanocytes and keratinocytes derived from different racial backgrounds and were examined by electron microscopy. Melanosomes transferred to keratinocytes were categorized as individual or in various clusters. Melanosome size was also determined for individual and clustered melanosomes. Results indicate that, in our model system, melanosomes in keratinocytes from different racial backgrounds show a combination of clustered and individual melanosomes. When keratinocytes from dark skin were cocultured with melanocytes from (i) dark skin or (ii) light skin, however, recipient melanosomes were individual versus clustered in (i) 77% vs 23% and (ii) 64% vs 36%, respectively. In contrast, when keratinocytes from light skin were cocultured with melanocytes from (iii) dark skin or (iv) light skin, recipient melanosomes were individual versus clustered in (iii) 34% vs 66% and (iv) 39% vs 61%, respectively. These results indicate that recipient melanosomes, regardless of origin, are predominantly distributed individually by keratinocytes from dark skin, and in membrane-bound clusters by those from light skin. There were also differences in melanosome size from dark or light donor melanocytes. Melanosome size was not related to whether the melanosomes were distributed individually or clustered, however, in cocultures. These results suggest that regulatory factor(s) within the keratinocyte determine recipient melanosome distribution patterns

Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy

We review HB stars in a broad astrophysical context, including both variable and non-variable stars. A reassessment of the Oosterhoff dichotomy is presented, which provides unprecedented detail regarding its origin and systematics. We show that the Oosterhoff dichotomy and the distribution of globular clusters (GCs) in the HB morphology-metallicity plane both exclude, with high statistical significance, the possibility that the Galactic halo may have formed from the accretion of dwarf galaxies resembling present-day Milky Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the second-parameter problem is presented. A technique is proposed to estimate the HB types of extragalactic GCs on the basis of integrated far-UV photometry. The relationship between the absolute V magnitude of the HB at the RR Lyrae level and metallicity, as obtained on the basis of trigonometric parallax measurements for the star RR Lyrae, is also revisited, giving a distance modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are studied. Finally, the conductive opacities used in evolutionary calculations of low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and Space Scienc

Activation Of Β-Catenin Signaling In Cd133-Positive Dermal Papilla Cells Drives Postnatal Hair Growth

The hair follicle dermal papilla (DP) contains a unique prominin-1/CD133-positive (CD133+) cell subpopulation, which has been shown to possess hair follicle-inducing capability. By assaying for endogenous CD133 expression and performing lineage tracing using CD133-CreERT2; ZsGreen1 reporter mice, we find that CD133 is expressed in a subpopulation of DP cells during the growth phase of the murine hair cycle (anagen), but is absent at anagen onset. However, how CD133+ DP cells interact with keratinocytes to induce hair regenerative growth remains unclear. Wnt/β-catenin has long been recognized as a major signaling pathway required for hair follicle morphogenesis, development, and regeneration. Nuclear Wnt/β-catenin activity is observed in the DP during the hair growth phase. Here we show that induced expression of a stabilized form of β-catenin in CD133+ DP cells significantly accelerates spontaneous and depilation-induced hair growth. However, hair follicle regression is not affected in these mutants. Further analysis indicates that CD133+ DP-expressed β-catenin increases proliferation and differentiation of epithelial matrix keratinocytes. Upregulated Wnt/β-catenin activity in CD133+ DP cells also increases the number of proliferating DP cells in each anagen follicle. Our data demonstrate that β-catenin signaling potentiates the capability of CD133+ DP cells to promote postnatal hair growth

Activation of β-Catenin Signaling in CD133-Positive Dermal Papilla Cells Drives Postnatal Hair Growth

<div><p>The hair follicle dermal papilla (DP) contains a unique prominin-1/CD133-positive (CD133+) cell subpopulation, which has been shown to possess hair follicle-inducing capability. By assaying for endogenous CD133 expression and performing lineage tracing using <i>CD133-CreER</i>^<i>T2</i>; <i>ZsGreen1</i> reporter mice, we find that CD133 is expressed in a subpopulation of DP cells during the growth phase of the murine hair cycle (anagen), but is absent at anagen onset. However, how CD133+ DP cells interact with keratinocytes to induce hair regenerative growth remains unclear. Wnt/β-catenin has long been recognized as a major signaling pathway required for hair follicle morphogenesis, development, and regeneration. Nuclear Wnt/β-catenin activity is observed in the DP during the hair growth phase. Here we show that induced expression of a stabilized form of β-catenin in CD133+ DP cells significantly accelerates spontaneous and depilation-induced hair growth. However, hair follicle regression is not affected in these mutants. Further analysis indicates that CD133+ DP-expressed β-catenin increases proliferation and differentiation of epithelial matrix keratinocytes. Upregulated Wnt/β-catenin activity in CD133+ DP cells also increases the number of proliferating DP cells in each anagen follicle. Our data demonstrate that β-catenin signaling potentiates the capability of CD133+ DP cells to promote postnatal hair growth.</p></div

Nuclear β-catenin is detected in the DP during anagen.

<p>Skin biopsies of normal C57BL/6 mice were collected at the indicated age and processed for paraffin sections. (<b>A-F</b>) Expression of β-catenin (green color) was visualized by immunofluorescence staining and counterstained with DAPI (blue nuclei). The DP was circled by white dashed lines in each hair follicle. (<b>J-L</b>) Same β-catenin immunostaining as in (A-F) (green color) without DAPI counterstaining. (<b>M-R</b>) DAPI staining of skin tissue sections used in (A-F) (blue nuclei). Scale bar: 100 μm</p

Expression of ΔN-β-catenin in CD133+ DP cells accelerates hair follicle differentiation.

<p>5-μm-thick paraffin sections from P35 <i>CD133-CreER</i>^<i>T2</i>; <i>Rosa-rtTA; tetO-Ctnnb1</i>^ΔN mutant mice and control littermates were processed for immunofluorescence staining of following markers: Sox9 for outer root sheath (control: <b>A</b>; mutant: <b>E</b>); Gata3 for inner root sheath (control: <b>B</b>; mutant: <b>F</b>); AE13 and AE15 for hair keratins (control: <b>C</b>, <b>D</b>; mutant: <b>G</b>, <b>H</b>); versican for anagen DP (control: <b>I</b>; mutant: <b>J</b>). Sections were nuclear counterstained with DAPI (blue). <b>K</b>. The numbers of versican+ DP cells in each hair follicle were counted and compared between <i>CD133-CreER</i>^<i>T2</i>; <i>Rosa-rtTA; tetO-Ctnnb1</i>^ΔN mutant mice and control littermates (mean ± s.d). A minimum of three skin biopsies from three pairs of mutant and control mice was analyzed. Two-tailed paired Student’s t-test was employed to calculate statistical significance. (<b>L-M</b>) β-catenin expression in hair follicle was examined by immunohistochemistry. Images shown are representative of at least three replicates at each indicated age. Scale bars: 200 μm for A-J; 100 μm for L-M.</p

Endogenous CD133 expression in postnatal murine hair follicles and lineage tracing using <i>ZsGreen1</i> reporter mice.

<p>(<b>A-F</b>) Frozen sections of back skin biopsies of normal C57BL/6 mice at each indicated age were immunostained with an anti-CD133 antibody. CD133 was expressed in a subpopulation of cells in the DP (circled by white dashed line) of P28 to P38 anagen hair follicles (<b>A-E</b>) but not in hair follicles that in catagen or later (<b>F</b>). (<b>G-L</b>) Lineage tracing of CD133+ DP cells using <i>CD133-CreER</i>^<i>T2</i>; <i>ZsGreen1</i> reporter mice. The DP is co-stained for the expression of alkaline phosphatase (red), which is a specific DP marker. GFP+ cells were first detected in DPs at P28 (<b>G</b>) and present throughout the entire anagen (<b>H-K</b>). An average of 20% of telogen hair follicles contained a small population of GFP+ cells in the DP (<b>L</b>). (<b>M</b>-<b>R</b>) Images of ZsGreen1 expression (green) in CD133+ DP cells during the hair cycle without staining for alkaline phosphatase expression. Green fluorescent DP cells were indicated with red arrows. For every indicated mouse age, at least three mice were analyzed. Scale bar: (A-F), 100 μm; (G-R), 200 μm</p

Increased proliferation in both matrix keratinocytes and DP cells in <i>CD133-CreER</i>^<i>T2</i>; <i>Rosa-rtTA; tetO-Ctnnb1</i>^ΔN hair follicles.

<p>Co-expression of Ki67 (green) and Lef1 (red) was examined in skin samples collected from <i>CD133-CreER</i>^<i>T2</i>; <i>Rosa-rtTA; tetO-Ctnnb1</i>^ΔN mice and control littermates at P32 (control: <b>A</b>; mutant: <b>E</b>) and P35 (control: <b>B</b>; mutant: <b>F</b>). Paraffin slides from BrdU-incorporated skin biopsies co-stained with anti-versican antibody showing enlarged DP compartment in hair follicles of from <i>CD133-CreER</i>^<i>T2</i>; <i>Rosa-rtTA; tetO-Ctnnb1</i>^ΔN mice with increased numbers of proliferating DP cells and matrix cells (<b>G</b>) than in littermate controls (<b>C</b>). Cyclin D1 staining indicated accelerated cell cycle progression in hair matrix cells when ΔN-β-catenin was expressed in CD133+ DP cells (<b>H</b>). Images shown are representative of at least three replicates at each indicated age. Total cell number (<b>I</b>) and number of Lef1+ DP cells (<b>J</b>) in each hair follicle at P28 and P35 were counted and compared between <i>CD133-CreER</i>^<i>T2</i>; <i>Rosa-rtTA; tetO-Ctnnb1</i>^ΔN mice and control littermates. 20 hair follicles were counted for each mouse (mean ± s.d.). For each indicated age, at least three pairs of mutant and control mice were used. Scale bars: 200 μm for A-C and E-G; 100 μm for D and H.</p

Expression of ΔN-β-catenin in CD133+ DP cells does not block hair follicle regression.

<p>Back skin biopsies from <i>CD133-CreER</i>^<i>T2</i>; <i>Rosa-rtTA; tetO-Ctnnb1</i>^ΔN mutant mice (<b>H-K</b>) and control littermates (<b>D-G</b>) were stained with H&E and photographed at indicated stages. Scale bars: 100 μm. (<b>L</b>) The numbers of hair follicles at P35 were counted and compared between <i>CD133-CreER</i>^<i>T2</i>; <i>Rosa-rtTA; tetO-Ctnnb1</i>^ΔN mutant mice and control littermates (mean ± s.d.). A minimum of three skin biopsies from three pairs of mutant and control mice was analyzed. Two-tailed paired Student’s t-test was employed to calculate statistical significance.</p