Introduction
The Pit-1, which is also called growth hormone factor-1, is a pituitary specific transcription factor that has been shown to positively regulate the expression of GH, prolactin (PRL) and thyrotrophin b subunit (TSH-b) (Nelson et al., 1988) and to play a role in pituitary cell differentiation and proliferation (Anderson and Rosenfeld, 1994). Mutations in the Pit-1 gene lead to the absence of growth hormone and pituitary hypoplasia in mice (Li et al., 1990) and a syndrome of congenital hypothyroidism, dwarfism, and prolactin deficiency in human (Pfaffle et al., 1992). Therefore, the Pit-1 gene may be a good candidate for genetic-marker associated effects upon growth traits. Detecting genetic variations in the Pit-1 gene and relating them to growth traits could be helpful in the discovery of useful genetic markers that can be used to facilitate selection and breeding through MAS programs.
Polymorphisms in the Pit-1 gene have been associated with production traits in pigs and cattle. Pit-1 was found to be related to weaning weight, average daily gain (Yu et al., 1995), backfat thickness (Yu et al., 1995; Stancekova et al., 1999), birth weight (Yu et al., 1996), and lean to fat ratio in pigs (Stancekova et al., 1999). In cattle, pit-1 was found to be associated with body weight, and milk, protein, and fat yields (Renaville et al., 1997).
The objectives of this study were to examine the Pit-1 gene for possible mutations using PCR-SSCP and PCR-RFLP, and to test the association of these polymorphisms with growth traits in Angus beef cattle.