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W Chavin

Publications and source records attributed to W Chavin.

At least 55 records · Page 3Linked to original sources
PubMed1975

Ultrastructure of the integumental melanophores of the Australian lungfish, Neoceratodus forsteri.

The integumental melanophores of Australina lungfish, Neoceratodus forsteri, were examined by light and electron microscopy and found to possess essentially the same structural characteristics observed in other vertebrates. The epidermal melanophores are located in the intermediate epidermis and possess round perikarya and slender dendrites extending into nearby intercellular spaces. The dermal melanophores are found immediately below the basement membrane as well as in the deeper dermis. These cells possess flattened nuclei and dendrites running parallel to the basement membrane. Each melanophore contains numerous oval or elliptical, intensely electron-dense melanosomes, relatively large mitochondria, systems of vacuolar endoplasmic reticulum, groups of free RNP particles, and some microfilaments. Only a few, short microtubules could be demonstrated in the perinuclear cytoplasm of the dermal melanophore, while a relatively large number of late premelanosomes are found both in perikarya and dendritic processes of epidermal melanophores. These premelanosomes exhibit a particulate internal structure in cross section. Both melanosomes and premelanosomes occur singly in the cytoplasm of epidermal cells, thereby confirming the existence of the epidermal melanin unit in the lowest vertebrates thus far examined electron microscopically.

Animals↗
PubMed1975

Ultrastructure of the integumental melanophores of the South Americal lungfish (Lepidosiren paradoxa) and the African lungfish (Protopterus sp.).

The integumental melanophores of two genera of lungfish, Lepidosiren paradoxa and Protopterus sp. were examined by light and electron microscopy. Both species possess both epidermal and dermal melanophores with fine structural characteristics basically similar to those of other vertebrates. The epidermal melanophores of both species are located in the intermediate epidermis, and possess thin perikarya containing round nuclei, and slender dendrites extending into the nearby intercellular spaces. The dermal melanophores occur immediately beneath the basement membrane, and possess flat perikarya and dendrites running horizontally between the collagen fibers of the dermis. The integument of both species does not possess an epidermal melanin unit or a dermal chromatophore unit. As in other vertebrates, each melanophore contains numerous oval, electron-opaque melanosomes, relatively large mitochondria, vacuolar endoplasmic reticula, and groups of RNP particles. Although micro filaments running randomly between other organelles occur regularly, microtubules were not demonstrated. Premelanosomes at various stages of differentiation were best illustrated in the dermal melanophores of Protopterus, and it is concluded from the observation of their fine structure that the morphological development of lungfish melanosomes closely parallels that of higher vertebrates. On the basis of melanophore morphology, Lepidosiren and Protopterus appear to be more closely related to each other than to Neoceratodus.

Africa↗
PubMed1975

Fetal bovine serum: a multivariate standard.

Chemical and endocrine parameters were investigated in commercially available fetal bovine sera intended for use as culture media supplements. A high degree of serum variability was present both within and between suppliers in all major categories investigated. It is suggested that caution be employed in the interpretation of results from experiments utilizing serum supplements without specific quantitation of possible interfering or modulating factors.

Animals↗
PubMed1975

Melanogenesis in human melanomas.

A number of biochemical aspects of melanogenesis were studied in 15 variously melanized human melanomas. The tryosinase activity was correlated with the degree of melanoma varied from 3,667 to 46,183 tryosinase units, in partially melanotic melanoma it varied from 14 to 75 tryrosinase units. The subcellular distribution of tryrosinase activity was limited to the particulate fraction )144,000 x g) of the partially melanotic and amelanotic melanomas. However, the melanotic melanomas contained the enzyme in both particulate and soluble fractions, with the greater tyrosinase activity in the particulate fraction. Electrophoretic resolution of tyrosinase isozymes in the soluble fraction or lipase-solubilized tyrosinase derived from the particulate fraction revealed three isozymes in melanotic melanomas. The isozyme of intermediate mobility always was the dominant form. In partially melaotic melanomas, the solubilized tyrosinase showed six isozymes. Three were similar to those of melanotic melanomas. The remaining three isozymes showed slower mobilities, possibly with greater molecular weights than the isozymes derived from melanotic melanomas. Inhibitors of tyrosinase were present in melanomas. Increased tyrosinase activity occurred after storing the homogenate at 0-4degree, removing of supernatant from the homogenate sediment, and washing the 144,000 x g particulate fraction, which suggested the presence of water-soluble, loosely bound inhibitor (s) in the soluble fraction of partially melanotic melanoma. Another inhibitor was released from the 144,000 x g particulate fraction of melanotic melanoma after lipase digestion. These substances inhibit both the isolated dominant tyrosinase isozyme(human) and mushroom tyrosinase. As inhibition of tyrosinase activity may produce regression of abnormal cell growth, the inhibitors may provide an approach to melanoma chemotherapy.

Catechol Oxidase↗