Polymorphism in the first intron of follicle stimulating hormone beta gene in three Chinese pig breeds and two European pig breeds.

Follicle stimulating hormone (FSH) is a pituitary gonadotropin that plays a key role in the regulation of gonadal function in mammal. The gonadotropic hormones are composed of two subunits, the common alpha subunit and the hormone-specific beta subunit, which determine the binding to specific receptors and induction of biological response. The aim of this study was to investigate the polymorphism of the first intron of FSH-beta gene present in different pig breeds and its influence on the expression of FSH-beta gene. Genomic DNA was isolated from blood of three Chinese local pig breeds and two European pig breeds. The first intron of FSH-beta gene was amplified by polymerase chain reaction (PCR) and the PCR product was then determined by sequencing. The correlation between the expression level of FSH-beta gene and the sequence polymorphism was evaluated by RT-PCR using 29 heterozygous pig breeds. Three patterns of the PCR amplified fragments were observed in five different pig breeds. They are 500bp, 220bp, and 500/220bp in length representing three different genotypes with respect to the size of the first intron of FSH-beta gene. After sequencing the whole intron 1 of FSH-beta, we have found that the different size of the PCR amplified fragments was attributed to an insertion element, which was only found in the larger fragment. The insertion, specific in pig genome, showed high similarity to short interspersed nucleotide elements (SINE). Moreover, The Chinese pig breeds, Xiang, Nuogu and Kele pig, exhibited a statistically significant higher frequency of the allele with this SINE in FSH-beta gene than the European pig breeds did. To elucidate whether the SINE insertion affects the expression of FSH-beta gene, 29 heterozygous Chinese and European pig breeds were tested by RT-PCR. The results confirmed that the major transcript in the heterozygous pigs was from SINE- allele but not detected from SINE+ allele. These data suggested that the SINE insertion negatively regulated the expression of FSH-beta gene and the dominant character related to propagation was gained from the SINE- allele of FSH-beta locus in heterozygous breeds of pigs.