ARPP-16 mRNA is up-regulated in the longissimus muscle of pigs possessing an elevated growth rate

Selection for increased growth rate in farm and laboratory animals has been used to develop lines with increased body and muscle weights. However, ver y little is known about the underlying molecular pathways and how their con stitutive genes influence this process. In this study, the differential dis play-reverse transcription PCR (DDRT-PCR) method was employed to identify l ongissimus muscle genes that are differentially expressed between a line of pigs selected for increased 200-d weight and a randomly selected control l ine. A 590-bp DDRT-PCR cDNA product was identified and isolated based on it s greater abundance in the longissimus muscle of the select line relative t o the control line animals. This DDRT-PCR product has 89% identity to the e nd of the 3'-untranslated region of the bovine 16-kDa cAMP-regulated phosph oprotein (ARPP-16) cDNA sequence. Reverse transcription PCR (RT-PCR) amplif ication of the porcine homologue of ARPP-16 and subsequent sequencing estab lished that the DDRT-PCR product corresponds to the 3'-end of the porcine A RPP-16 transcript. Semiquantitative RT-PCR verified that ARPP-16 is up-regu lated in the select line and determined that the relative expression level of ARPP16 mRNA is approximately fourfold higher (P < .01) in the select tha n in the control animals. The deduced amino acid sequence of ARPP-16 is hig hly homologous to the deduced amino acid sequences of bovine, human, and ra t ARPP-16, and RT-PCR with ARPP-16 specific PCR primers indicated that this gene is expressed in many different porcine tissues. The porcine homologue of the 19-kDa cAMP-regulated phosphoprotein (ARPP-19) was also amplified b y RT-PCR, cloned, and sequenced. The deduced amino acid sequence of ARPP19 differs from ARPP-16 only by the addition of 16 N-terminal amino acids. In all tissues studied, ARPP-19 mRNA was detected by RT-PCR amplification; how ever, the relative expression level of ARPP-19 mRNA was not differentially expressed between the select and control line animals (P > .05). The fourfo ld relative increase in ARPP-16 mRNA expression in the select line animals indicates that this gene may play an important role in the molecular pathwa y(s) that regulate postnatal skeletal muscle growth in the pig.