摘要:

Metastases from certain primary tumors frequently exhibit specific organ preference. Animal models have been developed to induce in a reproducible fashion the formation of organ‐specific metastases by malignant melanoma cells. Some of these models rely on the use of immunodeficient mice, which can support the growth of murine as well as human malignant melanomas. Moreover, immunodeficient mice, because of their diminished ability to mount an effective immune response, allow the expression of malignant properties (e.g., preferential colonization of certain organs), which are intrinsic to transplanted melanoma cells. This review discusses the relevant factors (and limitations) of some of the animal models used to study the in vivo properties of melanoma cell

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1993.tb00619.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

To learn more of the role of calcium in the regulation of melanogenesis, we have used direct manipulation of medium calcium and pharmacological modulation of intracellular calcium to examine the consequences on unstimulated and cyclic AMP elevated tyrosinase activity and melanin synthesis and distribution in B16 melanoma cells.In unstimulated cells, calcium is clearly inhibitory to tyrosinase activity. However, in cells stimulated with cAMP‐elevating agents the requirement for extracellular calcium was changed such that cells required a minimum of 0.4–0.6 mmol medium calcium for maximum tyrosinase response to these agents.Paradoxically, pharmacologically increasing intracellular calcium in cAMP‐stimulated cells with ionophore inhibited tyrosinase activity, and the calcium‐lowering agent TMB8 and the calcium channel blocker verapamil both stimulated tyrosinase activity.When melanin synthesis was measured in cAMP‐stimulated cells, TMB8 was found to significantly increase the sensitivity and the maximum melanogenic response to α‐MSH, suggesting the presence of at least one level of endogenous calcium inhibitory control operative in these cells. In addition, TMB8 changed the distribution of melanin between the cell and the medium such that, in the presence of α‐MSH and TMB8, significantly more melanin was secreted into the medium.These data suggest that calcium is required for several steps in melanogenesis, having an apparently inhibitory effect on pre‐tyrosinase activity in unstimulated cells, but also showing evidence of a positive role in cyclic AMP‐stimulated tyrosinase activity, as well as a further possible inhibitory role in melanin mo

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1993.tb00620.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Mammalian tyrosinase exists in a variety of subcellular locations and maturation states that result from a complex post‐translational processing with possible regulatory implications. So far, SDS‐PAGE has proven to be the method of choice for the resolution of tyrosinase isoforms. However, the relatively poor sensitivity of the currently available specific activity stain based on incubation of the gels with L‐dopa until the formation of melanin has severely limited the use of electrophoresis in regulation studies. Two alternative staining procedures are presented and discussed. The first one involves the fluoro‐graphic detection of radioactive melanin after incubation of the gels in the presence of L‐[3‐14C]‐dopa. A similar method has already been used by others (Tsukamoto et al., 1992, Pigment Cell Res. [Suppl.]2:84–89), but its performance has not yet been compared to the one of the dopa procedure. The sensitivity of this method can be varied by adjusting the isotopic dilution of the tracer and/or the time of exposure of the gel, but it is at least ten times higher than the one of the colorimetric stain. Moreover, the intensity of the bands is proportional to the initial tyrosinase activity over a wide range. Using this procedure, the activity present in the different subcellular fractions of melanocytes in culture can be easily detected. The second procedure involves the formation of a colored adduct between dopaquinone and MBTH. Its sensitivity is also more than one order of magnitude higher than the one obtained with L‐dopa alone, and comparable to the one of the fluorographic method, but, as opposed to this latter, the complete staining can be performed

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1993.tb00621.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The occasional occurrence of primary extra‐cutaneous malignant melanomas (MM) has led to the hypothesis that melanocytes derived from the neural crest may be arrested in their migration and may undergo an in situ malignant transformation. However, aggregates of nevus cells have only rarely been identified by histological examination in a few organs other than skin and eye. Tyrosinase is a melanin biosynthetic enzyme that is considered one of the most specific markers of melanocytic differentiation. We have at‐tempted to detect cells committed to the melanocytic lineage, in human tissues, by means of tyrosinase gene expression. Total RNA was extracted from normal and neoplastic tissues and analyzed using a highly sensitive reverse transcription PCR assay with primers specific for the tyrosinase gene. Peripheral blood mononuclear cells (PBMC) from healthy subjects were used as negative controls. Tyrosinase transcripts were identified in a wide range of normal organs such as skin, lymph nodes, antrum, colon, kidney, lung, testis, ovary, breast, and peripheral nerve. Tyrosinase RNA was also detected in neoplastic samples including benign cutaneous nevi, lymph nodes involved by MM, breast carcinoma, liposarcoma, malignant lymphoma, and schwannoma. PBMC from patients with meta‐static MM were also positive, while no positivity was detected in blood specimens from patients with other cancers.Therefore, it appears likely that cells expressing the tyrosinase gene are present in a wide range of human tissues. Although these cells still have to be accurately identified, one could propose that they might correspond to either fully differentiated melanocytes, melanocytic precursors, or Schwann cells bearing potentialities of melanocytic differentiation. Occurrence of at least some cases of primary extra‐cutaneous MM may be ascribed to any one of these possib

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1993.tb00622.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Dendrite formation and extension, which comprise a characteristic morphology of human normal melanocytes in the skin, represent one of the functional activities of melanocytes, the ability to transfer melanosomes into neighboring keratinocytes. However, the morphology of the melanocyte in vitro is usually quite different from that observed in vivo. it is probably due to the hyperproliferative condition of the melanocytes in culture. No studies have ever compared the effects of a single factor on both dendricity and proliferation at the same time. Therefore, we have compared the effects of six growth‐promoting agents commonly used for melanocyte cultures on dendrite formation and proliferation.The addition of agents that increase the intracellular levels of cyclic adenosine monophosphate (cAMP)—dibutyryl cyclic adenosine monophosphate (db cAMP; 1 mM) or isobutylmethyl xanthine (IBMX; 0.1 mM)—had a strong effect on dendrite formation and a negative effect on proliferation. This was especially true with db cAMP. In the presence of 2% or 5% of heat‐inactivated fetal bovine serum (FBS), dendrite formation was significantly increased as was proliferation. The number of dendrites was decreased in the culture with 12‐o‐tetradecanoylphorbol‐13‐acetate (TPA), but cell growth was slightly increased. With human recombinant basic fibroblast growth factor (bFGF) (0.5, 1.0 ng/ml) in the presence of bovine pituitary extract (BPE) (60 μg/ml), cell growth was increased. With 2 ng/ml of bFGF, however, a strong inhibitory effect on proliferation was observed. However, dendrite formation was constant at all concentrations of bFGF tested (0.5, 1.0 or 2.0 ng/ml) with BPE (30 or 60 μg/ml).In this study, we have demonstrated that dendrite formation was suppressed by the reagents that stimulate melanocyte proliferation, and vice versa, with the only exception being heat‐inactivated FBS. Both dendrite formation and proliferation were induced by the heat‐inactivated FBS. This approach is crucial to the development of an adequate culture system for proliferation and/or dendrite formation of normal human melanocytes. It is necessary to keep these aspects in mind as we further investigate the biology of melanocytes, especially the cell‐to‐cell interactions between melanocytes and keratinocytes, involved in melanogenesis and melanin pigmentation in vivo. This study also provides practical and important information for a future reconstitutive skin system composed of melanocytes, keratinocytes, and fibroblasts i

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1993.tb00623.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Cytoskeletal construction of dermal chromatophores of Orgzias latipes was studied by immunofluorescence microscopy. A microtubule system was most prominent in melanophores where a large number of microtubules emanated from the center of the cell. Xanthophores had an arrangement basically similar to that of melanophores, though the radial pattern became more irregular in the peripheral region where intersecting wavy microtubules were quite frequent. Oval‐shaped leucophores exhibited the least‐developed microtubule system, where the limited number of microtubules formed a loose basket‐like architecture. Intermediate filaments were ubiquitously present in all types of chromatophores and were found to be vimentin‐immunoreactive. Examination of doubly‐labeled cells indicated that vimentin filaments had similar distribution patterns with microtubules. Orderly arranged bundles of actin filaments were found only in xanthophores, while in melanophores and xanthophores, actin expression was diffuse without displaying a conspicuous filamentous organization. Colchicine treatment induced depolymerization of microtubules and retraction of dendrites in varying degrees in cells in culture and in situ. Melanophores in culture are very sensitive to the treatment while xanthophores appeared to be more resistant in respect to the maintenance of cell m

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1993.tb00624.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The cells dissociated from developing embryos of Japanese flounder (Paralichthys olivaceus) are cultured in vitro to examine the developmental fate of their pigment cells in relation to establishment of bilaterally asymmetric integumental coloration in vivo. When neurula embryos are dissociated using trypsin–EDTA in Dulbecco's modified Ca2+–, Mg2+–free phosphate buffered saline and then cultured in vitro using L–15–based fetal calf serum–supplemented growth medium at 20°C, numerous pigment cells appear twice in the same culture with an interval of approximately 1 month even under similar culture conditions. The first group of pigment cells, which is relatively larger in cell size (about 70 μm wide) and lower in cell density, emerges within 12 hr after plating, whereas the second, which is far smaller in cell size (about 30 μm) and overwhelmingly higher in cell density than the first, does so about 1 month after plating. The timing of their appearances in vitro is in good accordance, respectively, with that observed for the larvae under normal development in vivo; the first group appears at the period corresponding to hatching, whereas the second at the period corresponding to the completion of metamorphosis. Light microscopic examinations disclose that each group of pigment cells is composed of black melanophores and reflecting leucophores, and that the population density of melanophores and leucophores in the first group at the climax of appearance is approximated as 1:4. Typical xanthophores that are distributed in the skin of the larvae of this species are scarcely observed in culture in vitro. Because of their dual synchronous appearances with about 1 month interval under the similar culture conditions, and because of their low proliferative activity during the periods from the first appearance to the second, it is presumed that both groups of pigment cells are installed with a clock set differently for their differentiation. Light and electron microscopic immunocytochemistry on cultured cells using the HNK–I antibody, which marks avian migratory neural crest cells, both disclose that the antibody cross–reacts with all these pigment cells, and that a certain number of immunoreactive unpigmented cells exist even at the time of the second appearance of pigment cells. These findings would imply that the second group of pigment cells served in a form of undifferentiated propigment cells up to metamorphosis, at which they start to differentiate under control of a clock presumably set

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1993.tb00625.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0893-5785    

DOI:10.1111/j.1600-0749.1993.tb00626.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY