[Research on Alu element inserted mutation in porcine FSH beta subunit gene]

The inserted fragment of FSH beta subunit gene in Laiwu pigs, an excellent local pig breed in North China, Duli pigs and Landrace pigs was amplified, cloned and sequenced. Sequence analysis showed that the length of the fragments inserted between +809 bp and +810 bp of the published sequences (D00621) were 275 bp, 277 bp and 274 bp in Laiwu, Duli and Landrace pigs, respectively. And the poly (A)s in these inserted fragments were 17, 19 and 16 adenines, respectively. They were all shorter than those in Taihu pigs(292 bp and 32 adenines, respectively) reported formerly. According to the RNA polymerase III promoter structure and Alu I restriction enzyme site in the inserted fragment, it should be regarded as an Alu element. FSH beta subunit gene was considered as one candidate gene of pig litter size trait, while RNA polymerase III promoter could promote the transcription of the neighboring chromosome sequence so as to control the expression of FSH beta subunit gene or other genes. As a result, the major difference of the inserted fragment among different pig breeds was originated from the length of poly (A) end. So it was assumed that the poly (A) structure in the inserted fragment could influence the pig litter size. Because Laiwu pigs with genotype AA had 1.2 litter size more than those with genotype BB, it could be concluded that FSH beta subunit gene was related with pig litter size traits or linked with the genes of which, and the poly(A) structure in this Alu element played a critical role.