**3.4 The polymorphisms of these genes**

550 A Bird's-Eye View of Veterinary Medicine

quality traits and blood parameters have been reported in this region. Porcine *CGA* gene is mapped between 58,190,063 and 58,192,283 on chromosome 1, and 21 QTLs have been mapped to the corresponding region, most of which are fat related traits. The position of *TSHB* gene on porcine chromosome 4 is from 109,815,329 to 109,816,276. 49 QTLs including ADG, backfat thickness (BFT) and meat quality related traits have been mapped to this position. Unfortunately, *TRHR* and *TSHR* genes had not yet been annotated in Sscrofa 9 in

Radiation hybrid (RH) mapping is a kind of somatic cell genetics tool for mapping candidate genes into a framework of microsatellites/sequence-tagged sites. First, RH panels are constructed by using a lethal dose of X-rays to fragment the chromosomes of the donor cell and the chromosome fragments with known genetic markers are retained randomly in the host cells. The frequency of breakage between pairs of markers in a panel of RH clones can be used to calculate the relative physical distances of the genetic markers or genes. Several porcine RH panels have been produced, among which the whole-genome highresolution IMpRH panel constructed by Yerle et al. (1998) is the most frequently used one. The porcine *TRHR* gene was localized to the microsatellite *SW969* on chromosome 4 by RH mapping using the IMpRH panel (Jiang et al., 2011). 44 Quantitative trait loci affecting BFT, daily gain, and carcass and meat quality traits have been mapped to the same region. *TSHR* gene has been mapped between microsatellites *SW1083* and *SW581* on porcine chromosome 7 (Sato et al., 2006), and 50 QTLs including BFT, ADG, carcass length and muscle related

TRH is present not only in the hypothalamus but also in many other brain loci as a neuromodulator / neurotransmitter. Besides, expression of *TRH* gene is found in gastrointestinal tract, pancreas, reproductive tissues, heart, spleen, adrenals and thymus. Its receptor, *TRHR* is also found in gastrointestinal tract, pancreas, testis and adrenals. Paracrine effects of TRH on gastrointestinal tract and pancreas have been suggested. Furthermore, *TSHR* is widely expressed in many organs and tissues such as pituitary, heart, skeletal muscle and adipose. Species-specific expression of HPT genes in certain tissues might exist. For example, *TRHR* was detected in medaka spleen (Mekuchi et al., 2010) but undetectable in bovine spleen (Takata et al., 1998), and *TSHB* has been reported in the liver and reproductive organs of red drum (Cohn et al., 2010) but undetectable in the same organs

Tissue distribution of HPT genes in pigs have been investigated by using real-time quantitative RT-PCR with RNA samples from 15 different organs/tissues including brain, hypot4halamus, pituitary, thyroid, lung, kidney, gastrointestinal tract, muscle and fat tissue (Jiang 2011). Highest expression level of *TRH* was found in the brain, and considerable level of *TRH* also expressed in testis, spleen, fat tissue, small intestine and pancreas in addition to hypothalamus. Porcine *TRHR* mRNA was detected in almost all the investigated organs/tissues except the spleen, with high expression levels in the brain, hypothalamus,

the year 2009.

**3.2 The RH mapping** 

traits have been mapped to the same position.

**3.3 Expression analysis** 

of ducks (Hsieh et al., 2007).

Polymorphism in human *TRH* gene has been reported to be associated with blood pressure variations and hypertension (Kokubo et al., 2006). By re-sequencing the whole coding region of porcine *TRH* gene, eight sequence variations were identified (Jiang 2011). Among these polymorphisms, only ss325994920 (Figure 2) is a missense mutation which would bring a Val to Met amino acid mutation into pFE22 and pSE14 peptides.

Mutations in the *TRHR* could result in central hypothyroidism which causes growth retardation, pudginess and sluggishness (Collu et a., 1997). Further *TRHR* polymorphism has been identified responsible for human lean body mass variations in a genome-wide association study (Liu et al., 2009). Re-sequencing the coding sequences and flanking regions of porcine *TRHR* gene identified seven polymorphic loci (Figure 5a). Two of them locate in the intron 1 which has been proven to encompass important regulatory elements.

Mice with *CGA* gene knockout were viable, but exhibited severe growth insufficiency and infertility (Kendall et al., 1995). While no inactivating mutations of *CGA* gene has been detected in humans and mice, cases of nonsense mutations of *TSHB* gene have been continuously reported in humans which cause growth retardation and fat metabolism disorders (McDermott et al., 2002; Baquedano et al., 2010). 14 new polymorphic loci of porcine *CGA* gene (Figure 5b) and 5 polymorphisms of *TSHB* gene (Figure 5c) were identified and confirmed by re-sequencing (Jiang et al., 2011b). Four of the *CGA* polymorphisms locate in the promoter region. The single nucleotide polymorphism ss181129018 of *TSHB* gene locates on the first coding exon and brings amino acid change to the signal peptide of TSH β subunit.

*TSHR* is sensitive to point mutations and most of the reported human mutations existed in the last exon 10 (Davis et al., 2006). Re-sequencing the last exon of porcine *TSHR* gene detected three polymorphisms in the exon (Figure 5d), but all were synonymous mutations.
