Pigment types of various color genotypes of horses

Hair samples of various colors of horses were analyzed for content of both eumelanin and pheomelanin by a procedure using high performance liquid chromatography. The results are in accord with generally accepted genetic hypotheses accounting for the various colors. However, the results support the hypothesis that the chestnut/sorrel group of colors is conditioned by the extension locus, not the brown locus. The results also indicate that the brown locus is a likely contributor to some rare color phenotypes.     

Pink-eyed dilution, a coat color mutation in the Japanese field vole (Microtus montebelli)

Inheritance of dilute coat color with pink eye in the Japanese field vole (Microtus montebelli) was investigated by mating of the dilute mutant with a normal agouti vole and a white vole. As the results, it was cleared that an autosomal recessive gene p is responsible for the pink-eyed dilution in M. montebelli.     

影响麦长管蚜体色变化的主导因素

研究麦长管蚜Macrosiphum avenae(Fabricius)体色变化生态主导因素,田间红色麦长管蚜种群对不同抗蚜性寄主的反应和自然条件下,不同体色麦长管蚜的生殖力以及后代种群体色变化情况。结果显示:在实验温度范围内,麦长管蚜种群中红体色蚜虫所占比例随温度升高而增加,在28,29,30,31℃时,红体色蚜虫所占比例分别为6.66%,38.30%,70.60%和65.24%。麦长管蚜体色变化过程中,温度起到重要的作用,而与光周期和寄主营养的关系甚微。红体色麦长管蚜在不同抗蚜性的品种上其种群消长情况存在差异。田间红绿体色麦长管蚜经2代观测,平均蚜量比值分别为9.96和15.85,生殖力差异不显著。在小麦抽穗期到乳熟期红体色麦长管蚜个体比例随着田间条件的改变逐代升高(分别由第1代的17.55%和14.70%增至第2代的29.80%和42.2%)。     

Molecular and pharmacological characterization of dominant black coat color in sheep

Dominant black coat color in sheep is predicted to be caused by an allele E ^D at the extension locus. Recent studies have shown that this gene encodes the melanocyte stimulating hormone receptor (MC1-R). In mouse and fox, naturally occurring mutations in the coding region of MC1-R produce a constitutively activated receptor that switches the synthesis from phaeomelanin to eumelanin within the melanocyte, explaining the black coat color observed phenotypically. In the sheep, we have identified a Met→Lys mutation in position 73 (M73K) together with a Asp → Asn change at position 121 (D121N) showing complete cosegregation with dominant black coat color in a family lineage. Only the M73K mutation showed constitutive activation when introduced into the corresponding mouse receptor (mMC1-R) for pharmacological analysis; however, the position corresponding to D121 in the mouse receptor is required for high affinity ligand binding. The pharmacological profile of the M73K change is unique compared to the constitutively active E92K mutation in the sombre mouse and C123R mutation in the Alaska silver fox, indicating that the M73K change activates the receptor via a mechanism distinct from these previously characterized mutations. Received: 18 September 1997 / Accepted: 14 October 1998     

Coat color dilution in mice because of inactivation of the melanoma antigen MART-1

Melanoma antigen recognized by T cells 1 (MART-1) is a melanoma-specific antigen, which has been thoroughly studied in the context of immunotherapy against malignant melanoma and which is found only in the pigment cell lineage. However, its exact function and involvement in pigmentation is not clearly understood. Melanoma antigen recognized by T cells 1 has been shown to interact with the melanosomal proteins Pmel17 and OA1. To understand the function of MART-1 in pigmentation, we developed a new knockout mouse model. Mice deficient in MART-1 are viable, but loss of MART-1 leads to a coat color phenotype, with a reduction in total melanin content of the skin and hair. Lack of MART-1 did not affect localization of melanocyte-specific proteins nor maturation of Pmel17. Melanosomes of hair follicle melanocytes in MART-1 knockout mice displayed morphological abnormalities, which were exclusive to stage III and IV melanosomes. In conclusion, our results suggest that MART-1 is a pigmentation gene that is required for melanosome biogenesis and/or maintenance.     

Allelic heterogeneity at the equine KIT locus in dominant white (W) horses

White coat color has been a highly valued trait in horses for at least 2,000 years. Dominant white (W) is one of several known depigmentation phenotypes in horses. It shows considerable phenotypic variation, ranging from ~50% depigmented areas up to a completely white coat. In the horse, the four depigmentation phenotypes roan, sabino, tobiano, and dominant white were independently mapped to a chromosomal region on ECA 3 harboring the KIT gene. KIT plays an important role in melanoblast survival during embryonic development. We determined the sequence and genomic organization of the ~82 kb equine KIT gene. A mutation analysis of all 21 KIT exons in white Franches-Montagnes Horses revealed a nonsense mutation in exon 15 (c.2151C>G, p.Y717X). We analyzed the KIT exons in horses characterized as dominant white from other populations and found three additional candidate causative mutations. Three almost completely white Arabians carried a different nonsense mutation in exon 4 (c.706A>T, p.K236X). Six Camarillo White Horses had a missense mutation in exon 12 (c.1805C>T, p.A602V), and five white Thoroughbreds had yet another missense mutation in exon 13 (c.1960G>A, p.G654R). Our results indicate that the dominant white color in Franches-Montagnes Horses is caused by a nonsense mutation in the KIT gene and that multiple independent mutations within this gene appear to be responsible for dominant white in several other modern horse populations.     

Chromosomal assignment of the canine melanophilin gene (MLPH): a candidate gene for coat color dilution in Pinschers

Pinschers affected by coat color dilution show a specific pigmentation phenotype. The dilute pigmentation phenotype leads to a silver-blue appearance of the eumelanin-containing fur and a pale sandy color of pheomelanin-containing fur. In Pinscher breeding, dilute black-and-tan dogs are called "blue," and dilute red or brown animals are termed "fawn" or "Isabella fawn." Coat color dilution in Pinschers is sometimes accompanied by hair loss and a recurrent infection of the hair follicles. In human and mice, several well-characterized genes are responsible for similar pigment variations. To investigate the genetic cause of the coat color dilution in Pinschers, we isolated BAC clones containing the canine ortholog of the known murine color dilution gene Mlph. RH mapping of the canine MLPH gene was performed using an STS marker derived from BAC sequences. Additionally, one MLPH BAC clone was used as probe for FISH mapping, and the canine MLPH gene was assigned to CFA25q24.     

The lichen cushion: A functional perspective of color and size of a dominant growth form on glacier forelands

Mat-forming lichens dominating high-latitudinal habitats vary in color and geometry. Widespread species are light greenish yellow (usnic acid) and reflect solar radiation, whereas melanic species absorbing most solar wavelengths are spatially more restricted. Color thereby influences lichens’ energy budget and thus their hydration and photosynthetically active periods. By using well-defined cushions from early successional stages on glacier forelands – three melanic^(m) and three usnic^(u) mat-forming lichens with hair-like branches (Alectoria ochroleuca^(u), Gowardia nigricans^(m)), hollow terete branches (Cladonia uncialis^(u), Cetraria muricata^(m)), and flat branches (Flavocetraria nivalis^(u), Cetraria islandica^(m)) – we quantified hydration traits and analyzed how color and cushion size affect water loss rate (WLR) and duration of active periods. Main findings: 1) WLR declined with cushion size and was highest in melanic lichens. 2) Active periods were longer for usnic than for melanic lichens and increased with size in all groups. 3) Size, color, and taxon nested in color significantly influenced WLR and duration of active periods in linear mixed models. 4) Hair lichen cushions had shorter active periods than growth forms with terete or flat branches due to their more open canopy architecture and lower water holding capacity (WHC). 5) WHC measured for isolated branches highly underestimated WHC for intact cushions.     

Total body water and ECFV measured using bioelectrical impedance analysis and indicator dilution in horses.

The purposes of this study were 1) to determine the compartmentation of body water in horses by using indicator dilution techniques and 2) to simultaneously measure bioelectrical impedance to current flow at impulse current frequencies of 5 and 200 kHz to formulate predictive equations that could be used to estimate total body water (TBW), extracellular fluid volume (ECFV), and intracellular fluid volume (ICFV). Eight horses and ponies weighing from 214 to 636 kg had catheters placed into the left and right jugular veins. Deuterium oxide, sodium thiocyanate, and Evans blue were infused for the measurement of TBW, ECFV, and plasma volume (PV), respectively. Bioelectrical impedance was measured by using a tetrapolar electrode configuration, with electrode pairs secured above the knee and hock. Measured TBW, ECFV, and PV were 0.677 +/- 0.022, 0.253 +/- 0.006, and 0.040 +/- 0.002 l/kg body mass, respectively. Strong linear correlations were determined among measured variables that allowed for the prediction of TBW, ECFV, ICFV, and PV from measures of horse length or height and impedance. It is concluded that bioelectrical impedance analysis (BIA) can be used to improve the predictive accuracy of noninvasive estimates of ECFV and PV in euhydrated horses at rest.     

Explicit evidence for a missense mutation in exon 4 of SLC45A2 gene causing the pearl coat dilution in horses

Four loci seem responsible for the dilution of the basic coat colours in horse: Dun (D), Silver Dapple (Z), Champagne (CH) and Cream (C). Apart from the current phenotypes ascribed to these loci, pearl has been described as yet another diluted coat colour in this species. To date, this coat colour seems to segregate only in the Iberian breeds Purebred Spanish horse and Lusitano and has also been described in breeds of Iberian origin, such as Quarter Horses and Paint Horse, where it is referred to as the ‘Barlink Factor’. This phenotype segregates in an autosomal recessive manner and resembles some of the coat colours produced by the champagne CH^CH and cream C^Cr alleles, sometimes being difficult to distinguish among them. The interaction between compound heterozygous for the pearl C^prl and cream C^Cr alleles makes SLC45A2 the most plausible candidate gene for the pearl phenotype in horses. Our results provide documented evidence for the missense variation in exon 4 [SLC45A2:c.985G>A; SLC45A2:p.(Ala329Thr)] as the causative mutation for the pearl coat colour. In addition, it is most likely involved as well in the cremello, perlino and smoky cream like phenotypes associated with the compound C^Cr and C^prl heterozygous genotypes (known as cream pearl in the Purebred Spanish horse breed). The characterization of the pearl mutation allows breeders to identify carriers of the C^prl allele and to select this specific coat colour according to personal preferences, market demands or studbook requirements as well as to verify segregation within particular pedigrees.     

Novel insights into Sabino1 and splashed white coat color patterns in horses

Within the framework of genome‐wide analyses using the novel Axiom^® genotyping array, we investigated the distribution of two previously described coat color patterns, namely sabino1 (SBI), associated with the KIT gene (KI16+1037A), and splashed white, associated with the PAX3 gene (ECA6:g.11429753C>T; PAX3^C70Y), including a total of 899 horses originating from eight different breeds (Achal Theke, Purebred Arabian, Partbred Arabian, Anglo‐Arabian, Shagya Arabian, Haflinger, Lipizzan and Noriker). Based on the data we collected we were able to demonstrate that, besides Quarter horses, the PAX3^C70Y allele is also present in Noriker (seven out of 189) and Lipizzan (three out of 329) horses. The SB1 allele was present in three breeds (Haflinger, 14 out of 98; Noriker, four out of 189; Lipizzan one out of 329). Furthermore, we examined the phenotypes of SB1‐ and PAX3^C70Y‐carrier horses for their characteristic white spotting patterns. None of the SB1/sb1‐carrier horses met the criteria defining the Sabino1 pattern according to current applied protocols. From 10 heterozygous PAX3^C70Y‐carrier horses, two had nearly a splashed white phenotype. The results of this large‐scale experiment on the genetic association of white spotting patterns in horses underline the influence of gene interactions and population differences on complex traits such as Sabino1 and splashed white.