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At least 19 recordsLinked to original sources
PubMed1978

Stimulation of dendritogenesis in the epidermal melanocytes of newborn mice by melanocyte-stimulating hormone.

The number of dendrites and the total length of dendrites in the epidermal melanocytes positive for the dopa reaction were shown to increase when newborn mice were injected with alpha-MSH or DBc-AMP. Moreover, both indices of the degree of dendritogenesis increased when skin explants of newborn mice were cultured in medium containing alpha-MSH or DBc-AMP. Electron-microscopic observation showed that the number of melanosomes was also increased by alpha-MSH treatment. Many mature melanosomes were observed in the dendrites of the epidermal melanocytes of alpha-MSH-injected mice. Highly dendritic melanocytes seem to be the cells stimulated by MSH to form melanosomes and translocate them to dendrites. Dendritogenesis stimulated by the hormone was suppressed by actinomycin D or cycloheximide, suggesting that the dendritogenesis in the epidermal melanocytes requires de novo transcription and translation.

Animals↗
PubMed1976

Effects of melanocyte stimulating hormone and theophylline on human melanocytes in vitro.

The effects of MSH on the human melanocyte in vitro were studied. The addition of MSH up to the concentration of 40 mug/ml into the culture medium did not produce appreciable change on the morphology of the melanocyte. The melanocyte, however, responded to the simultaneous addition of MSH and theophylline with marked increase in the length and complexity of the dendritic process. Melanin synthesis, as indicated by the uptake of tyrosine in the presence of an inhibitor of protein synthesis, was remarkably activated by the simultaneous addition of MSH and theophylline. MSH alone activated the melanin synthesis only slightly, but the increase in the uptake of tyrosine was significant statistically. These results were discussed in terms of the MSH-cyclic AMP cascade in which theophylline worked as an inhibitor of cyclic AMP phosphodiesterase, and increased the intracellular level of cyclic AMP by inhibiting catabolism of cyclic AMP.

Cyclic AMP↗
PubMed1976

Stimulation by melanocyte stimulating hormone and dibutyryl adenosine 3'5'-cyclic monophosphate of DNA synthesis in human melanocytes in vitro.

The proliferation of human melanocytes in vitro was stimulated by MSH. This stimulation was further intensified by the simultaneous addition of theophylline with MSH. Theophylline alone stimulated proliferation moderately. Dibutyryl cyclic AMP strongly stimulated the proliferation, but sodium butyrate, 5'-AMP and cGMP did not. The stimulation by dibutyryl cyclic AMP was continued up to 4 days so far tested. These findings are directly opposed to those on mouse melanoma cells in culture which responded with retarded growth to MSH and cyclic AMP. It is suggested that the difference of proliferation control may explain the different reaction of the melanocyte and the melanoma cells. The epidermal melanocytes seem to belong to the exceptional group of the cells which responded to cyclic AMP with accelerated proliferation.

Adult↗
PubMed1976

Melanocyte-stimulating hormone receptors on cultured guinea-pig melanocytes.

Guinea-pig melanocytes in mixed epidermal cell cultures bind melanocyte-stimulating hormone in a distinct focal surface area in their perinuclear field and thus follow the same pattern previously described for Cloudman melanoma cells. The labeling index ranged from 18 to 34%. Pretreatment of cultures with trypsin leads to destruction of melanocyte-stimulating hormone receptors whereas neuraminidase has no such effect.

Cell Line↗
PubMed1979

The epidermal melanocyte system in patients with malignant melanoma. Quantitative and qualitative investigation of dopa positive melanocytes.

The results from this study indicate that in 5 out of 22 patients increased activity of the melanocytes in the vicinity (a few mm to 1 cm) of the tumour is to be found. In 8 out of 22 patients suspect cells were also found a few mm to 1 cm from the tumour; a finding which accounts for the frequent recurrence following close excision of the melanoma. Furthermore, it was ascertained that the total melanocyte population is increased in 14 out of 22 patients. An increased melanocyte population can contain a greater number of instabile cell forms that can easier be malignantly transformed under the influence of external factors.

Cell Count↗
PubMed1979

Pure melanocyte cultures: differential serum requirements of guinea pig keratinocytes and melanocytes in primary epidermal cell cultures.

Contrary to melanocytes guinea pig keratinocytes do not attach and grow in primary epidermal cell cultures if plated in media containing guinea pig serum. This phenomenon is based on the low content or lack of guinea pig serum of a factor(s) promoting keratinocyte attachment. This factor, which is contained in fetal calf serum, binds to the keratinocyte cell surface and can be removed by trypsin. Guinea pig epidermal cell cultures plated in medium containing guinea pig serum therefore lead to pure or almost pure melanocyte cultures.

Animals↗
PubMed1979

Immunological block to synthetic alpha-melanocyte-stimulating hormone: melanocyte interaction by antibodies isolated from cell-column immunoadsorbents.

Antibodies to formalin-fixed, syngeneic melanoma cells were prepared in mice, purified by immunoaffinity chromatography, and tested for binding activity to viable melanoma cells. The radiolabeled antibodies detected congruent to 9 X 10(6) melanoma antigenic sites/cell. The calculated average association constant (Ka) for the antibody population was 7 to 10 X 10(7) M-1. The antibody was shown to block the binding of melanocyte-stimulating hormone in competitive cell surface binding studies. Results are discussed conceptually in terms of the potentially important role that the humoral immune response may play in the phenomenon of tumor progression.

Animals↗
PubMed1979

Serum melanocyte-stimulating hormone levels and pituitary melanocyte-stimulating hormone content during pseudopregnancy in the rat.

Pseudopregnancy (PSP) was induced in rats by vaginal stimulation and the levels of MSH in serum and pituitary were examined. One hour after vaginal stimulation, the serum MSH level was increased, and a cyclical variation was observed by the second day of PSP. There were two surges of about 50 pg/ml, one in the morning and the other at night. On the sixth day of PSP, the pattern of serum levels still showed two peaks, but while the nocturnal peak remained at 50 pg/ml, the diurnal value was halved. The pituitary MSH content also underwent cyclical variations; the lowest levels coincided with the peak levels in serum. These observations raise the possibility that MSH is involved in PSP.

Animals↗
PubMed1978

Changes of organelles associated with the differentiation of epidermal melanocytes in the mouse.

Electron microscopic observations on normally differentiating and alpha-MSH (melanocyte-stimulating hormone)-treated epidermal melanocytes of newborn mouse skin were carried out. The process of melanocyte differentiation from premelanosome-containing melanoblasts was investigated in detail with respect to melanosomes as markers. Melanoblasts containing unmelanized premelanosomes gradually decreased in number after birth, while the number of melanocytes rapidly increased. The epidermis of alpha-MSH-treated 3-day-old mice and normal 6-day-old mice contained melanocytes with numerous fully melanized melanosomes, and with no or only a few melanoblasts. Changes in other organelles in differentiating melanocytes were also noticeable. Golgi apparatus and RER (rough endoplasmic reticulum) decreased in number during the normal or alpha-MSH-induced differentiation of the epidermal melanocytes, though the number of mitochondria showed no notable change. The number of SER (smooth endoplasmic reticulum) per cell did not change in the cells of newborn mice, while in alpha-MSH-treated cells the number increased significantly. These results led us to an assumption that Golgi apparatus or RER transforms into other forms of organelles including melanosomes and SER during the differentiation of melanocytes.

Animals↗
PubMed1978

Organ culture of mammalian skin and the effects of ultraviolet light and testosterone on melanocyte morphology and function.

Scrotal skin of black Long-Evans rats and human thigh skin were maintained in vitro as organ cultures for as long as 14 days, and examined histologically using the combined skin splitting and Dopa techniques. Selected rat skin cultures received testosterone in the culture medium and/or were irradiated with ultraviolet light (290-320 nm UVL). With increased time in culture, scrotal melanocytes round up and there is an increase in epidermal pigmentation. Human skin behaves similarly; after eight days in vitro human melanocytes also become rounded, but remain strongly Dopa-positive. Addition of exogenous testosterone to cultured rat skin maintains dendritic morphology of melanocytes, but cell body size is still reduced. UVL irradiation stimulates melanocytes in rat skin cultures, maintaining their dendritic morphology and increasing epidermal and dermal pigmentation. Cultured skin receiving both UVL and testosterone illustrates a synergistic effect. Electron microscopic examination of cultured rat skin shows the presence of large melanosome complexes in keratinocytes, much larger than those found in vivo. Melanocytes appear to be active as they contain an extensive Golgi zone, rough endoplasmic reticulum, and melanosomes in various stages of formation. Dermis contained many dermal melanocytes and macrophages laden with melanosomes, correlating with the increased visible dermal pigmentation in vitro. This UVL stimulation of melanocytes in our skin organ cultures contrasts with the lack of melanogenic stimulation found in melanoma cell cultures. Our findings suggest that the intact epidermal melanin unit may be necessary for UVL stimulation of melanocytes.

Animals↗
PubMed1975

Mitotic activity in non-neoplastic melanocytes in vivo as determined by histochemical, autoradiographic, and electron microscope studies.

Mitotic figures were demonstrated in the differentiated melanocytes of normal epidermal and nonepidermal tissues without the presence of external stimuli. These dividine melanocytes were present in human and mouse skin, mouse hair, chick feathers, and embryonic chick retinal pigment epithelium. In normal adult human epidermis, dividing melanocytes, though rare, were found in the nonstimulated areas. L-3,4-dihydroxyphenylalanine reaction on the melanocytes during mitosis demonstrated activity of the melanin-forming enzyme, tyrosinase, and ultrastructural studies demonstrated the characteristic melanosomes in variour stages of maturation. Other ultrastructural characteristics of the melanocytes during mitosis, except for the Golgi apparatus, which was smaller and less complex, were similar to those seen in well-differentiated nondividing melanocytes. Autoradiographic studies of thymidine incorporation into mouse skin indicated that 0.7% of epidermal melanocytes, when slightly stimulated, are in the S phase. Thus, in vivo differentiation of non-neoplastic melanocytes (to produce pyrosinase and melanosomes) does not preclude their replication by mitotic division.

Animals↗
PubMed1975

The gene action and function of two dopa oxidase positive melanocyte mutants of the fowl.

Ultrastructural and autoradiographic analysis revealed the developmental genetic differences between the dopa oxidase positive pk and I mutations of the fowl. The differences were revealed by the results of five measurements involving homozygous mutant melanocytes, heterozygous melanocytes, and standard melanocytes at each of the loci. The measurements were: ultrastructural comparisons of melanosomes in pigmented epithelial (PE) and neural crest derived (NC) melanocytes, the number of 3H-dopa and 3H-leucine grains/mu2 of melanosome, the 3H-dopa/3H-leucine ratio, and the percentage of cytoplasmic 3H-leucine grains that were melanosomal. The pk mutation altered both PE and NC melanosomes. +/pk melanocytes were characterized by suppressed 3H-dopa/mu2 and 3H-dopa/3H-leucine values. +/pk cells, however, had the same percentage of melanosomal 3H-leucine grains as the "pk" standard. The I mutation altered only NC melanosomes. +/I melanocytes were characterized by 3H-dopa/mu2 and 3H-dopa/3H-leucine values similar to the "I" standard. +/I cells had a lower percentage of melanosomal 3H-leucine grains that the "I" standard, however. These data suggest that pk is a structural mutation affecting melanin binding to the premelanosome, while I seems to be a control gene mutation partially suppressing the production of premelanosomal components in NC melanocytes.

Animals↗
PubMed1979

The effects of UVB and 7, 12, dimethylbenz(alpha)anthracene (DMBA) on epidermal melanocytes of the tail in C57BL mice.

The morphological and numerical changes in the epidermal melanocyte system of the tail of C57BL mice were studied after exposure to 7, 12 dimethylbenz(alpha)anthracene (DMBA) followed by UVB irradiation. The dorsal aspect of the tail was exposed for 5 days per week, for a total duration of 10 weeks, to a daily dosage of 0.1 J/cm2 UVB (peak 310 nm). Once a week, 0.2 ml of 0.15% DMBA in acetone was locally applied to the irradiated areas. Biopsies were studied by the combined skin-splitting DOPA and electron microscopic techniques. After 10 weeks of DMBA treatment the following changes were observed: DMBA treatment the following changes were observed: the original brick-like arrangement of melanocytes became confluent, melanocytes were irregularly shaped, dendrites shortened and clumped together, and the outer root sheaths of the hair follicles became covered with melanocytes. There was a significant increase in the number of DOPA positive melanocytes at the end of the first week in DMBA and DMBA + UVB treated skin. Ultrastructurally, an increase in melanosome formation in melanocytes and transfer into keratinocytes was found, as well as redistribution of melanosomes from singlets and doublets into larger groups. Damage of melanocytes by the DMBA treatment was seen, but no inflammation or tumor formation was observed.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1979

Effects of aging and chronic sun exposure on melanocytes in human skin.

Both aging and sun exposure have well-documented effects on the human melanocyte system. Paired biopsies of habitually exposed and nonexposed skin from adjacent anatomic sites were obtained from 8 donors aged 28 to 80 yr in order to study the combined effect of chronic actinic irradiation and chronologic aging. Density of dopa-positive melanocytes was roughly twofold higher in the exposed than in the nonexposed skin at all ages, suggesting an irreversible effect of sun exposure. Melanocyte density declined approximately 6 to 8% of the surviving population per decade in both sites. Dopa-positivity of individual melanocytes was consistently greater in the chronically exposed skin than in the nonexposed skin of the same subject and did not vary with age. These data strengthen and expand earlier observations of age-related melanocyte changes, and explain the apparent paradox of a generalized increase in pigmentation and simultaneous decrease in melanocyte density which frequently accompany advancing age. In addition, the present study suggests that the principal effect of chronic sun exposure on the human pigmentary system is not premature "aging" as currently recognized histologically, but rather activation and/or proliferation of the exposed melanocytes.

Adult↗
PubMed1978

Mitotic activity of epidermal melanocytes in UV-irradiated mouse skin.

The role of mitosis in the increase in the epidermal melanocyte population following repeated ultraviolet (UV) irradiation has been studied in C57B1 mice. Cumulative labeling with 3H-methyl-thymidine (3HTdr) was used in combination with autoradiography. A 4-6 fold increase in the melanocyte population was associated with an isotope labeling of 65-80% of the melanocytes. This indicates that cell division during the irradiation period can account for the total increase in the number of melanocytes. Labeled melanocytes were also found in the epidermis from unirradiated skin. Thus, the epidermal melanocytes seem to constitute a dynamic cell population under continuous renewal.

Animals↗
PubMed1979

on the extracellular sheath of dermal melanocytes in nevus fusco-ceruleus acromiodeltoideus (Ito) and Mongolian spot. An ultrastructural study.

The dermal melanocytes in the lesions of nevus of Ito and Mongolian spot were shown to possess the extracellular sheath composed of both fine filaments and granules (2-5 nm in diameter). In the case of nevus of Ito, the granular component appeared to predominate in the shealth, which measured up to 3 micrometers in width and was estimated to cover about 97% of the total surface of dermal melanocytes. No ultrastructural changes were appreciable on the melanocyte shealth in nevus of Ito according to the difference in the age of patients (39 and 64 years), or in the lasting period of the dermal melanocytosis. By contrast, the melanocyte sheath in the case of Mongolian spot was much less developed than in nevus of Ito, predominantly filamentous in texture, and showed a marked decline with advance of the age of infants (from 2 mo to 6 yr). Many of the dermal melanocytes in Mongolian spot showed a partial disruption of their cytolemma, resulting in discharges of melanosomes free into the connective tissue matrix. Significance of these findings was discussed in relation to the differtial fate of melanocytes within the human dermis.

Adult↗