Biomedical subjects
Publications and source records attributed to F Hu.
Choroidal melanocytes differentiate and cease to divide early in postnatal life. They have characteristic organelles, the melanosomes, which are formed from tyrosine in a reaction catalyzed by tyrosinase. As animals become old, enzyme activity declines and the melanosomes show changes that are quantitatively and qualitatively correlated to the animal's increasing age.
Choroidal melanocytes of the eyes of postnatal animals are classified as postmitotic terminally differentiated cells. They have specific granules, the melanosomes, which undergo changes qualitatively and quantitatively correlated to the animal's increasing age. Epidermal melanocytes, which normally divide only on demand or by stimulation, are classified as intermittent mitotic cells. During their development, lentigines and nevi of the skin show progressive ultrastructural and cytochemical changes similar to those in the choroidal cells, and thus may be considered as aging populations of skin melanocytes. These facts have led to the conclusion that choroidal melanocytes may be used advantageously as a model for studying changes in cells from maturation to senescence.
Somatic cell hybrids from viral fusions of murine melanoma (PAZG) X Chinese hamster peritoneal cells (CH) were compared with respect to surface antigenicity, karyotype and tumorigenicity. One line, F57-(9), which arose from the hybridization of two CH cells and one PAZG cell, had slight (6%) CH chromosome loss but 80%PAZG chromosome loss after 10 months in culture. These cells expressed CH antigens strongly and PAZG antigens weakly. In comparison, another hybrid, F57-(7), formed from one CH and one PAZG cell, lost 20% of its chromosomes after 10 months in vitro. These cells had a stronger expression of PAZG antigens and weaker expression of CH antigens than F57-(9). These findings indicate a direct relationship between chromosome number and antigenicity; tumorigenicity, however, does not appear to depend on the chromosome numbers of the parental cells.
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Thioglycolate-induces peritoneal macrophages from melanoma-bearing mice (immune macrophages) or from control mice (control macrophages) were cultured with syngeneic melanoma cells (P51) to determine the surface characteristics of the effector cells during interaction and destruction of the target cells. After a short culture period (3 hours), immune macrophages had extensive connections via filopodia and ruffled membranes to the surfaces of the melanoma cells; control macrophages did not exhibit the same behavior. A dense region in the cytoplasm immediately beneath the macrophage plasmalemma was observed at the point of contact with the target tumor cell. With longer periods of culture (24 hours), effector cells began phagocytosis of the target cells; immune macrophages, however, had more fine filopodial connections and were more cytostatic than were controls. These observations indicate that one of the initial mechanisms of tumor cell destruction was contact-induced lysis, with phagocytosis playing a minor part.
Tyrosine hydroxylase, dopa oxidase, and peroxidase activities were studied in soluble fractions of B16 melanoma tumor homogenates by polyacrylamide gel disc electrophoresis. Stained gels were scanned photometrically and gel slices were assayed radiometrically. In these preparations, the two bands of tyrosine hydroxylating activity were completely separated from the peroxidase activity but coincided with two major bands of dopa oxidase activity. The third dopa oxidase band coincided with the single band of peroxidase activity. The soluble fraction of cultured cell homogenates had no peroxidase activity, but the two tyrosine hydroxylase bands coincided exactly with the two dopa oxidase bands. Therefore, in the soluble fraction of the murine melanoma bifunctional tyrosinase does exist as two electrophoretically separable forms which are independent of peroxidase.
Epidermal melanocytes were observed in the black but not in the white skin of black-and-white spotted guinea pigs. In experiments designed to determine whether melanocyte-stimulating hormone (MSH) affects the incorporation of thymidine by kerationcyte nuclei of the epidermal melanin unit, the labeling index was the same in all skin before MSH administration. After MSH injections, the level of (3H)thymidine incorporation in keratinocytes increased significantly in black skin but not in white. We suggest that through the mediation of melanocytes MSH indirectly afffects keratinocytes in the epidermal melanin unit.
Somatic cell hybrids were derived by fusing tumourigenic and melanogenic melanoma (PAZG) cells with normal diploid male mouse cells in vivo. Their chromosomal composition was equivalent to the sum of both parental genomes and included a Y chromosome lacking in the melanoma parent. Our study showed that in PAZG X C57BL hybrids (MP), tumourigenicity was suppressed but pigmentation was expressed.
Specific chromosomes in several mouse lines have interstitial C-bands. In situ hybridization studies indicate that these interstitial bands contain typical mouse satellite DNA.
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