The tyrosinase activity of Himalayan mouse skin homogenates was measured over a range of temperatures using two sensitive radiometric assay--namely, (1) the measurement of 14C-tyrosine incorporation into melanin, and (2) the measurement of 3HOH released as a by-product of 3H-tyrosine hydroxylation. Results show that Himalayan tyrosinase is maximally active at temperatures well below normal body temperature (15 degree C to 25 degree C). These results are in support of Danneel's visual observations ('41) that "ferment" activity of Himalayan rabbit skin is absent at temperatures above 25 degree C. Further results suggest the presence of a tyrosinase inhibitor in Himalayan mouse skin. First, removal of a low molecular weight fraction from Himalayan skin homogenates resulted in an increase in tyrosinase activity. Second, recombination of the low molecular weight fraction to the homogenate from which it was originally separated resulted in a decrease in tyrosinase activity when assayed at 37 degree C, but no decrease when assayed at 25 degree C. It is proposed that at the normal body temperature of 37 degree C, tyrosinase from Himalayan skin is strongly bound to an inhibitor. At lower body temperatures, the affinity of the enzyme for the inhibitor decreases, thus allowing the synthesis of melanin to increase. This change in affinity of the enzyme for the inhibitor could be regulated by temperature-induced conformational changes in either the enzyme or the inhibitor or both.
This scanning electron- and light-microscopic study traces the morphogenesis of the yolk-sac vascular system and extraembryonic coelom in the chick blastoderm. The fate of the mesodermal cells in both the area opaca vasculosa (AOV) and the area pellucida (AP) is followed, and the cellular patterning in these two areas is compared. We describe new details of the formation of coelom lining in the AOV, and new observations of the tendency of the intravascular blood island cells of the AOV to become flattened and attenuated. The morphogenesis of the blood system and coelom is analyzed in terms of polarized morphological patterns with coordinates in two modes:proximodistal (from the AP to the AOV) and dorsoventral (from the ectoderm to the endoderm). By highlighting differences in the methods of formation of blood vessels and coelom lining in the AP and AOV, this paper resolves some paradoxes in the literature.
The effect of temperature on pigment synthesis in adult and juvenile Himalayan mice was investigated. Since pigment synthesis only occurs in actively growing hair, adult mice were plucked to induce hair growth. The extent of darkening of the hair was recorded by photography against a reference scale. The presence of pigment granules in hair follicles was investigated histologically. Housing adult and juvenile mice at 15 degrees C results in the synthesis of pigment in growing hair follicles whereas housing at 30 degrees C results in the absence of pigment granules in the growing hair follicles.
We have investigated the temporal and the causal basis of blood tissue specification in the chick embryo. Earlier workers have shown that the prospective blood-forming area is specified in a horseshoe-shaped area at the posterior side of the embryo. We found that cultured explants from the posterior marginal zone at stages XI to XIII (consisting of the posterior marginal zone and part of Koller's sickle) have a high propensity to form haemoglobin (Hb), which could be inhibited at stage XI by adding antibody against basic fibroblast growth factor (bFGF) to the neutral culture medium; this treatment had no effect from stage XII onwards. The same result was found when whole embryos were cultured with an antiserum raised against bFGF, or with heparin. In another series of experiments, we found that cultured pieces from the inner-core of stage XIII epiblasts (with or without hypoblast tissue) were able to form Hb, whereas inner-core pieces from the pre-hypoblast stages, namely stages X and XI, did not form Hb. The capacity to form Hb, however, could be conferred upon the inner-core pieces from stage X epiblasts if bFGF at a concentration of 75–150 ng/ml was added to the culture medium. Furthermore, and most pertinently, the capacity to form Hb could be conferred on stage X inner-core pieces when they were co-cultured with hypoblast from a stage XIII embryo in a sandwich explant. Thus the inductive role of the hypoblast appears to be mediated via bFGF.(ABSTRACT TRUNCATED AT 250 WORDS)
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.