This study confirmed the characteristics of the coat color expression patterns of Korean brindle cattle(Chikso) and Hanwoo. And the mutation of genes related to the expression of coat color were systematically studied using molecular genetic methods. This study was conducted to better explain the mechanism of coat color gene expression cattle breeding and to establish a basis for impro ving the ratio of whole brindle color in Koream brindle cattle.

In the first experiment, the objective was to determine the breed differences in the 3''-untranslated region (UTR) of MC1R mRNA, which may be used to distinguish Korean brindle cattle (Chikso) from other breeds. We investigated the relationship between the variation of 3''-UTR of the MC1R mRNA and coat color among different breeds and the Korean brindle cattle with different coat colors. MC1R mRNA expression levels were determined in accordance with the coat color and hair colors of the tail. Total cellular RNA was extracted from the hair follicles of the tails in Hanwoo, Korean brindle cattle, Holstein and Hanwoo × Holstein crossbred cattle. After cDNA synthesis, PCR was performed. Sequences of the 3''-UTR of MC1R mRNA were analyzed. The 3''-UTR of the MC1R mRNA from different breeds of cattle did not show any variations. There were no variations in the 3''-UTR of the MC1R mRNA in Korean brindle cattle with different coat colors. The levels of MC1R mRNA expression in hair follicles of the tail varied substantially among the Korean brindle cattle with different coat colors, except yellow coat color. Correlation between the MC1R mRNA expression in the hair follicles of the tail and coat color may be present in the Korean brindle cattle, but not between the variations of 3''-UTR of MC1R mRNA and coat color.

In the second experiment, the aim was to determine the relationship between the coat color appearance of Korean brindle cattle and the changes of relevant hormone levels that may affect the hair pigmentation during different stages of growth and maturation. In mature cattle, levels of both ACTH and DHEA in Korean brindle cattle with brown color were significantly higher than those with black color (p<0.05). Levels of α-MSH in Korean brindle cattle with whole brindle (?50%) color were significantly higher than those with brown color (p<0.05). In calves of Korean brindle cattle at 2 to 6 months, the concentration of estradiol was significantly higher in calves with whole brindle color than those with part brindle color (p<0.05), when the coat color was first confirmed. After 6 month of coat color confirmation, levels of testosterone and ACTH increased in calves with part brindle color and were significantly higher than those with whole brindle color (p<0.05). In calves of Korean brindle cattle at 1 or 2 months, there were no significant differences in hormone levels of estradiol, ACTH, DHEA and α-MSH between the calves with brindle color and brown color, except estradiol before brindle color appearance. Changes of relevant hormone levels at different stages of growth and maturation may affect the pigmentation of coat during the development of cattle.

In the third experiment, the aim was to identify coat color associated genes that are differentially expressed in mature Korean brindle cattle (KBC) with different coat colors and in Hanwoo cows. KBC calves, before and after coat color appearance, were included. Total cellular RNA was isolated from the tail hair cells and used for microarray. The number of expressed coat color associated genes/probes was 5813 in mature KBC and Hanwoo cows. Among the expressed coat color associated genes/probes, 167 genes were the coat color associated genes listed in the Gene card database and 125 genes were the pigment and melanocyte genes listed in the Gene ontology_bovine database. There were 23 genes/probes commonly listed in both databases and their expressions were further studied. Out of the 23 genes/probes, MLPH, PMEL, TYR and TYRP1 genes were expressed at least two fold higher (p<0.01) levels in KBC with brindle color than either Hanwoo or KBC with brown color. TYRP1 expression was 22.96 or 19.89 fold higher (p<0.01) in KBC with brindle color than either Hanwoo or KBC with brown color, respectively, which was the biggest fold difference.
The hierarchical clustering analysis indicated that MLPH, PMEL, TYR and TYRP1 were the highly expressed genes in mature cattle. There were only a few genes differentially expressed after coat color appearance in KBC calves.

In the fourth experiment, the aim was to identify the correlation between coat color and expression of coat color-associated genes that are differentially expressed in Korean brindle cattle with different coat colors and in Hanwoo. Using Real Time PCR, we investigated relative levels of 11 coat color-associated gene tran scripts. Eleven coat color-associated genes transcripts were DCT-a, DCT-b, PPARG-a, PPARG-b, PMEL-a, PMEL-b, TYR-a, TYR-b, TYRP1-a, TYRP1-b and TYRP1-c. Levels of DCT-a, DCT-b, TYRP1-a, TYRP1-b and TYRP1-c transcripts in Korean brindle cattle with black coat color was significantly higher(p<0.05) than those in Hanwoo. Levels of DCT-a, DCT-b and TYRP1-a transcripts in Korean brindle cattle with brindle coat color was significantly higher(p<0.05) than those in Hanwoo.
The five out of 11 gene transcripts that were significant different in expression were determined by Real Time PCR. Experiments were repeated three times. The five genes transcripts were DCT-a, DCT-b, PPARG-a, TYRP1-b and TYRP1-c. Levels of DCT-a, DCT-b and TYRP1-b transcripts in Korean brindle cattle with black coat color was significantly higher(p<0.05) than those in Hanwoo. Levels of DCT-a and DCT-b Korean brindle cattle with brindle coat color and Korean brindle cattle with brown coat color were significantly higher(p<0.05) than those in Hanwoo.

As a result of this study, we could more fully understand the mechanism of the coat color expression patterns and regulation of highly expressed genes, and further improve the expression of whole brindle color in Korean brindle cattle.