GENOME-WIDE ASSOCIATION STUDY OF TESTES DEVELOPMENT INDICATORS IN ROOSTERS (Gallus gallus L.)

Reproductive ability is one of the main indicators of the male breeding value that depends primarily on the functional state of testes cells. Male fertility is defined by complex physiological processes affecting the formation of mature germ cells, i.e., spermatozoa in the process of spermatogenesis. The forming and accumulation of germ cells occur in the seminiferous tubules of the testes, therefore the gonad development can serve as an indicator characterizing spermatogenesis and the reproductive potential of males. A number of studies on farm animals, including poultry, have shown the genetic determinacy of this trait, with identification of respective single nucleotide polymorphisms (SNPs) and genes determining the male gonad growth and development. In the present investigation, a genome-wide association study (GWAS) of the testes development parameters in roosters (Gallus gallus L.) of the F2 resource population were conducted. For the first time, new significant SNPs and candidate genes (р < 1.05½104) determining gonad growth and development in roosters were identified. The aim of the research was to seek SNPs and identify genes associated with testes growth parameters in roosters. The object of the study were F2 roosters from a model resource population (n = 115) that was obtained by interbreeding two breeds, Russian White and White Cornish. DNA was extracted from feather pulp using a commercial kit DNK Extran-2 (OOO NPF Sintol, Russia) in accordance with the manufacturer’s protocol. Genotyping was carried out using the medium-density Illumina Chicken 60K SNP iSelect BeadChip chip. At the age of 63 days, the experimental birds were slaughtered and the mass and morphometric indices of testes (length and thickness) were examined. Based on the obtained genotypic and phenotypic data, the GWAS analysis was performed in F2 resource population roosters using PLINK 1.9 software. The examined population was characterized by a high coefficient of variation in the measured indices, 96.1 % for the testes mass and 39.1 % for the linear measurements. The mass and linear measurements of the left testis were 5-14 % higher (р  0.05) compared to the right testis. The GWAS analysis revealed 36 significant SNPs (р < 1.05½104) associated with testes growth and development parameters in 63-day-old cockerels, in particular with the mass, length and thickness of the testes, 3, 26 and 7 SNPs, respectively. SNPs were localized on chromosomes GGA1, GGA3, GGA6, GGA7, GGA12, GGA15, and GGA18. A total of 156 genes were identified in the regions of the detected SNPs, including 16 genes that coincided with the positions of these SNPs. In particular, the latter were one gene (WNT7A) associated with the testis mass, 13 genes (LHFPL1, GALNT3, TMEM198, CACNA2D3, CCDC66, CACNA1D, DENND6A, CELSR3, WNT7A, IP6K2, ERC2, ABHD6, and DEPDC5) associated with the testis length, and three genes (ESR1, POLE, and RNFT2) associated with the testis thickness. These data can be used in genomic selection of roosters aimed at increasing their reproductive potential.