Diverse developing mouse lineages exhibit high-level c-Myb expression in immature cells and loss of expression upon differentiation.
The c-myb gene encodes a sequence specific transactivator that is required for fetal hematopoiesis, but its potential role in other tissues is less clear because of the early fetal demise of mice with targeted deletions of the c-myb gene and incomplete of knowledge about c-myb's expression pattern. In the hematopoietic system, c-Myb protein acts on target genes whose expression is restricted to individual lineages, despite Myb's presence and role in multiple immature lineages. This suggests that c-Myb actions within different cell type-specific contexts are strongly affected by combinatorial interactions. To consider the possibility of similar c-Myb actions could extend into non-hematopoietic systems in other cell and tissue compartments, we characterized c-myb expression in developing and adult mice using in situ hybridization and correlated this with stage-specific differentiation and mitotic activity. Diverse tissues exhibited strong c-myb expression during development, notably tooth buds, the thyroid primordium, developing trachea and proximal branching airway epithelium, hair follicles, hematopoietic cells, and gastrointestinal crypt epithelial cells. The latter three of these all maintained high expression into adulthood, but with characteristic restriction to immature cell lineages prior to their terminal differentiation. In all sites, during fetal and adult stages, loss of c-Myb expression correlated strikingly with the initiation of terminal differentiation, but not the loss of mitotic activity. Based on these data, we hypothesize that c-Myb's function during cellular differentiation is both an activator of immature gene expression and a suppressor of terminal differentiation in diverse lineages. (+info)
WNT signaling in the control of hair growth and structure.
Characterization of the molecular pathways controlling differentiation and proliferation in mammalian hair follicles is central to our understanding of the regulation of normal hair growth, the basis of hereditary hair loss diseases, and the origin of follicle-based tumors. We demonstrate that the proto-oncogene Wnt3, which encodes a secreted paracrine signaling molecule, is expressed in developing and mature hair follicles and that its overexpression in transgenic mouse skin causes a short-hair phenotype due to altered differentiation of hair shaft precursor cells, and cyclical balding resulting from hair shaft structural defects and associated with an abnormal profile of protein expression in the hair shaft. A putative effector molecule for WNT3 signaling, the cytoplasmic protein Dishevelled 2 (DVL2), is normally present at high levels in a subset of cells in the outer root sheath and in precursor cells of the hair shaft cortex and cuticle which lie immediately adjacent to Wnt3-expressing cells. Overexpression of Dvl2 in the outer root sheath mimics the short-hair phenotype produced by overexpression of Wnt3, supporting the hypothesis that Wnt3 and Dvl2 have the potential to act in the same pathway in the regulation of hair growth. These experiments demonstrate a previously unrecognized role for WNT signaling in the control of hair growth and structure, as well as presenting the first example of a mammalian phenotype resulting from overexpression of a Dvl gene and providing an accessible in vivo system for analysis of mammalian WNT signaling pathways. (+info)
Procyanidin oligomers selectively and intensively promote proliferation of mouse hair epithelial cells in vitro and activate hair follicle growth in vivo.
We have previously reported that proanthocyanidins extracted from grape seeds possess growth-promoting activity toward murine hair epithelial cells in vitro and stimulate anagen induction in hair cycle progression in vivo. This report constitutes a comparison of the growth-promoting activity of procyanidin oligomers and the target cells of procyanidins in the skin. Results show that procyanidin dimer and trimer exhibit higher growth-promoting activity than the monomer. The maximum growth-promoting activity for hair epithelial cells with procyanidin B-2, an epicatechin dimer, reached about 300% (30 microM) relative to controls (= 100%) in a 5 d culture. Optimum concentration of procyanidin C-1, an epicatechin trimer, was lower than that of procyanidin B-2; the maximum growth-promoting activity of procyanidin C-1 was about 220% (3 microM). No other flavonoid compounds examined exhibit higher proliferative activities than the procyanidins. In skin constituent cells, only epithelial cells such as hair keratinocytes or epidermal keratinocytes respond to procyanidin oligomers. Topical application of 1% procyanidin oligomers on shaven C3H mice in the telogen phase led to significant hair regeneration [procyanidin B-2, 69.6% +/- 21.8% (mean +/- SD); procyanidin B-3, 80.9% +/- 13.0%; procyanidin C-1, 78.3% +/- 7.6%] on the basis of the shaven area; application of vehicle only led to regeneration of 41.7% (SD = 16.3%). In this paper, we demonstrate the hair-growing activity of procyanidin oligomers both in vitro and in vivo, and their potential for use as agents to induce hair growth. (+info)
Topical gene delivery to murine skin.
We topically applied naked plasmid DNA containing the luciferase or chloramphenicol acetyltransferase cDNA directly to mouse skin. Gene expression was detected in skin samples as early as 4 h after DNA application, plateaued from 16 to 72 h post-application, and had decreased significantly by 7 d post-application. Reporter gene activity following topical DNA delivery was comparable with that produced by intradermal injection of DNA. Plasmid DNA at concentrations > or =0.25 microg per microl were required to achieve maximal expression levels. Reporter gene expression following topical administration was largely confined to the superficial layers of the epidermis and to hair follicles. Surprisingly, certain cationic liposomes inhibited the efficiency of cutaneous gene transfer. This technique provides a simple, clinically relevant approach to deliver genes to the skin, with potential application in treating a variety of cutaneous disorders. (+info)
Association between mouse nude gene expression and the initiation of epithelial terminal differentiation.
Loss-of-function mutations in Whn (Hfh 11), a winged-helix/forkhead transcription factor, result in the nude mouse phenotype. To determine the whn expression pattern during development, we utilized mice in which a beta-galactosidase reporter gene was placed under the control of the wild-type whn promoter by homologous recombination (M. Nehls et al., 1996, Science 272, 886-889). Sites of reporter expression were confirmed by immunohistochemical staining for Whn protein or by in situ hybridization for whn mRNA. At all developmental stages, whn expression is restricted to epithelial cells. In addition to the skin and thymus, whn is expressed in the developing nails, nasal passages, tongue, palate, and teeth. In embryonic epidermis, suprabasal cells induce whn expression at the same time that terminal differentiation markers first appear. As the epidermis matures, whn promoter activity is found primarily in the first suprabasal layer, which contains keratinocytes in the early stages of terminal differentiation. In developing and mature anagen hair follicles, whn is expressed at high levels in the postmitotic precursor cells of the hair shaft and inner root sheath. Though principally associated with terminal differentiation, whn expression is also detected in progenitor cell compartments; in the hair bulb matrix and basal epidermal layer, a small subclass of cells expresses whn, while in the outer root sheath, whn promoter activity is induced as the follicle completes its elongation. Within these compartments, rare cells exhibit both whn expression and the nuclear proliferation marker Ki-67. The results suggest that whn expression encompasses the transition from a proliferative to a postmitotic state and that whn regulates the initiation of terminal differentiation. (+info)
UVB irradiation stimulates deposition of new elastic fibers by modified epithelial cells surrounding the hair follicles and sebaceous glands in mice.
UVB irradiation stimulates the synthesis of elastin in the skin of humans and experimental animals. In this study we localized the site and the cells that are responsible for the synthesis of murine dermal elastic fibers. SKH-1 hairless mice were irradiated with UVB and the skin removed for light microscopy, electron microscopy, in situ hybridization, immunohistochemistry, and biochemical studies. In response to chronic low doses of UVB there was an initial moderate increase in tropoelastin mRNA in the papillary dermis. By contrast, there was a continuous marked elevation of collagen alpha1(I) message localizing to sites of inflammatory cell influx throughout the upper and lower dermis. After 25 wk of UV irradiation there was a 2-fold increase in skin elastin, yet total collagen remained unchanged. Serial desmosine analysis from en face sections indicated the increase in elastin content was due to dermal elastic fibers, an increase in the size and number of the dermal cysts, and an increase in subpanniculus elastic fibers. Elastin stains of en face sections suggested that the elastic fibers in the upper dermis were exclusively derived from cells lining the epithelial root sheath and sebaceous glands. In response to UV irradiation, the elastic fibers increased in number and size, wrapping around these structures and aligning in both directions as long fibers parallel to the body axis. Electron micrographs indicated that modified epithelial cells in close proximity to the flattened epithelial cells that encircled the root sheath and sebaceous glands were the source of the elastic fibers. (+info)
Highly persistent label-retaining cells in the hair follicles of mice and their fate following induction of anagen.
We have identified some unusually persistent label-retaining cells in the hair follicles of mice, and have investigated their role in hair growth. Three-dimensional reconstruction of dorsal underfur follicles from serial sections made 14 mo after complete labeling of epidermis and hair follicles in neonatal mice disclosed the presence of highly persistent label-retaining cells associated with the first-generation follicle involved in the production of the first wave of hairs, commonly called the bulge. The label-retaining cells were most often found on the ventral surface of the first-generation follicle, five cell positions from the base, near the attachment site of the arrector pilorum muscle. No label-retaining cells were found in the hair canal, sebaceous gland, or hair germ. These label-retaining cells remained in the follicle following induction of anagen by plucking of the hairs. Surprisingly, they were not part of the first wave of mitotic activity following plucking, but instead underwent mitosis beginning 42 h after plucking. Label-retaining cells or their labeled daughters were not found in the hair germs through 48 h following induction of anagen by plucking, but instead remained in their subsebaceous follicular location even upon completion of the hair growth cycle 21 d later. These label-retaining cells are, therefore, unlikely to contribute to the formation of a new anagen follicle. (+info)
A rapid and dynamic regulation of GDNF-family ligands and receptors correlate with the developmental dependency of cutaneous sensory innervation.
Glial cell line-derived neurotrophic factor (GDNF) and neurturin (NTN) are members of the transforming growth factor-beta family and have been shown to elicit neurotrophic effects upon several classes of neurons including dopaminergic neurons, motoneurons, parasympathetic, sympathetic as well as primary sensory neurons. However, there is little information available on their roles in cutaneous innervation. Herein, we have studied the regulation of gdnf, ntn and the GDNF family receptors and examined their role in the development of facial cutaneous innervation in GDNF mutant mice. A dynamic spatial and temporal regulation of gdnf, ntn and their ligand binding receptors within the follicle-sinus complex correlate with development of distinct subclasses of sensory nerve endings. Furthermore, development of NGF-dependent myelinated mechanoreceptors, i.e. reticular and transverse lanceolate endings also require GDNF during ending formation and maintenance. In addition, ligand and receptor association seems to be intricately linked to a local Schwann cell-axon interaction essential for sensory terminal formation. Our results suggests that functionally specified nerve endings depend on different GDNF family members and that in contrast to neurotrophins, this family of neurotrophic factors may be acting at local sites of terminal Schwann cell-axon growth cone interactions and that they collaborate with neurotrophins by supporting the same populations of neurons but at different times in development. (+info)