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At least 1,369 records · Page 76Linked to original sources
PubMed1999

The melanocyte-stimulating hormone receptor (MC1-R) gene as a tool in evolutionary studies of artiodactyles.

The complete coding region of the melanocyte-stimulating hormone receptor (MC1-R) gene was characterized in species belonging to the two families Bovidae and Cervidae; cattle (Bos taurus), sheep (Ovis aries), goat (Capra hircus), muskox (Ovibos moschatus), roe deer (Capreolus capreolus), reindeer (Rangifer tarandus), moose (Alces alces), red deer (Cervus elaphus) and fallow deer (Dama dama). This well conserved gene is a central regulator of mammalian coat colour. Examination of the interspecies variability revealed a 5.3-6.8% divergence between the Cervidae and Bovidae families, whereas the divergence within the families were 1.0-3.1% and 1.2-4.6%, respectively. Complete identity was found when two subspecies of reindeer, Eurasian tundra reindeer (R.t. tarandus) and Svalbard reindeer (R.t. platvrhynehus), were analyzed. An rooted phylogenetic tree based on Bovidae and Cervidae MC1-R DNA sequences was in complete agreement with current taxonomy, and was supported by bootstrapping analysis. Due to different frequencies of silent vs. replacement mutations, the amino acid based phylogenetic tree contains several dissimilarities when compared to the DNA based phylogenetic tree.

Animals↗
PubMed2001

Effect of low levels of dietary tyrosine on the hair colour of cats.

Experiments were conducted to investigate the basis for the change in hair colour of black cats to reddish-brown. Black cats were given purified diets based on gelatin, casein plus lactalbumin, or crystalline amino acids as protein sources. Diets that caused the colour of hair to change to reddish-brown were associated with a reduction in melanin in hair (observed by direct microscopic examination), a decreased total melanin concentration and low concentrations of tyrosine in plasma. Reddish hair coat was induced in black kittens born to queens given a tyrosine-deficient diet during pregnancy. Black hair colour was maintained or restored by diets containing a high concentration of tyrosine or phenylalanine. Current dietary recommendations for dietary tyrosine and phenylalanine for cats are below those required to support maximal melanin synthesis in black cats. The requirement appears to be greater than a combination of 4.5 g tyrosine plus 12 g phenylalanine/kg diet but less than 24 g phenylalanine alone/kg diet.

Amino Acids↗
PubMed2003

Coat colour changes associated with cabergoline administration in bitches.

Cabergoline or bromocriptine were administered orally to 60 bitches at doses of 5 microg/kg and 15 microg/kg daily, respectively, for two to 45 days for the treatment of pseudopregnancy or for oestrus induction. Seven of the dogs which received cabergoline for more than 14 days developed coat colour changes from the second week of administration to the next coat shedding. Of these, fawn-coloured bitches developed a yellowish coat colour while Argentine boar hounds became black spotted, mainly on their extremities. In previous untreated oestrous periods, these bitches had shown no coat colour changes. It is concluded that a colour shift in certain haircoats of particular breeds could be mediated through the inhibition of the secretion of melanocyte-stimulating hormone by the administration of the dopaminergic agonist cabergoline for more than two weeks. Transient coat colour changes should be considered a possible side effect when planning long-term treatment with dopaminergic agonists in dogs.

Animals↗
PubMed1991

Hair pigmentation in transgenic mice.

A mouse tyrosinase minigene, mg-Tyrs-J, in which genomic 5' noncoding flanking sequence was fused to a mouse tyrosinase cDNA, was introduced into fertilized eggs of BALB/c albino mice. Six transformed mice that exhibited brown agouti hair with some variations in the intensity of pigmentation were obtained. By crossing the founder mice with BALB/c albino mice, transgenic lines and sublines were established. Each subline expressed a characteristic phenotype with their respective band patterns in Southern blot analysis. This indicates that the character is expressed by transgenes integrated at a single location of the chromosomes. The difference in phenotypes among sublines is probably due to the position effect of the chromatin where the transgene is integrated, although a possibility that modification in the nucleotide sequence of the transgene is responsible for the difference cannot be excluded at present.

Animals↗
PubMed1999

Genetic studies of the human melanocortin-1 receptor.

Genetic approaches have suggested a critical role for the melanocortin-1 receptor in the control of pigmentation. We showed that this gene is unusually polymorphic in European populations and that, of the many variants, three in particular appear to be associated with red hair or fair skin. Family studies suggest these are inherited as an autosomal recessive trait (or at least approximate to this in many families). To date all individuals with two of these three changes (homozygote or compound heterozygote) have red hair. Early functional studies are in keeping with defective signalling through MC1R. An interested and perhaps unexpected question relates to the evolutionary factors that have given rise to such variants. Two models can be proposed, that are based on multiple alleles with minor changes in function or genetic hitch-hicking.

Animals↗
PubMed1999

Molecular pharmacology of Agouti protein in vitro and in vivo.

Agouti protein and Agouti-related protein (Agrp) are paracrine signaling molecules that act by antagonizing the effects of melanocortins, and several alternatives have been proposed to explain their mechanisms of action. Genetic crosses in a sensitized background uncover a phenotypic difference between overexpression of Agouti and loss of Mc1r function, demonstrate that a functional Mc1r is required for the pigmentary effects of Agouti, and suggest that Agouti protein can act as an agonist of the Mc1r in a way that differs from alpha-MSH stimulation. In vitro, Agouti protein inhibits melanocortin action by two mechanisms: competitive antagonism that depends on the carboxyterminus of the protein, and downregulation of melanocortin receptor signaling that depends on the aminoterminus. Our findings provide evidence of a novel signaling mechanism whereby alpha-MSH and Agouti protein function as independent ligands that inhibit each other's binding and transduce opposite signals through a single receptor.

Agouti Signaling Protein↗
PubMed2003

Hair depigmentation is a biological readout for pharmacological inhibition of KIT in mice and humans.

Deregulated activation of the KIT receptor tyrosine kinase has been implicated in several human cancers and in inflammation, making it an attractive target for therapeutic intervention. Conversely, deficiencies in KIT signaling have been implicated in human and animal hair pigmentation disorders, reflecting a role for KIT in the development and function of melanocytes. The goal of this study was to explore the potential utility of hair depigmentation as a biological readout for systemic inhibition of KIT by SU11248 5-[5-fluoro-2-oxo-1,2-dihydroindol-(3Z)-ylidenemethyl]-2,4-dimethyl-1H-pyrrole-3-carboxylic acid (2-diethylaminoethyl)amide), an oral multitargeted tyrosine kinase inhibitor with antitumor and antiangiogenic activity through targeting platelet-derived growth factor receptors, vascular endothelial growth factor receptors, KIT, and FLT3. Oral SU11248 treatment induced dose-dependent depigmentation of newly regrown hair in depilated C57BL/6 mice. Similar effects were seen after administration of a KIT-neutralizing antibody. SU11248-induced hair depigmentation was reversible with cessation of treatment. Histological and immunohistochemical evaluation of mouse skin samples supported these observations and revealed that SU11248 has no effect on levels of KIT-positive melanocytes associated with hair follicles, indicating that the inhibitory effect is at the level of melanocyte function rather than their development/survival. Similar hair depigmentation has been noted in several cancer patients receiving SU11248 in phase I trials. Strikingly, patient scalp hair exhibits bands of depigmentation and pigmentation that correspond, respectively, to periods of treatment and dosing rest periods. These data demonstrate that hair pigmentation can serve as a dose-dependent, dynamic, biological readout for KIT inhibition in mice, and, apparently, in humans.

Animals↗
PubMed2002

Sexual selection, temperature, and the lion's mane.

The mane of the African lion (Panthera leo) is a highly variable trait that reflects male condition and ambient temperature. We examined the consequences of this variation in a long-term study of lions in the Serengeti National Park, Tanzania. Mane darkness indicates nutrition and testosterone and influences both female choice and male-male competition. Mane length signals fighting success and only appears to influence male-male assessment. Dark-maned males enjoy longer reproductive life-spans and higher offspring survival, but they suffer higher surface temperatures, abnormal sperm, and lower food intake during hot months of the year. Maned males are hotter than females, and males have lighter and/or shorter manes in hotter seasons, years, and habitats. This phenotypic plasticity suggests that the mane will respond to forecasted increases in ambient temperature.

Aggression↗