Roles of the proteasome and inhibitor of DNA binding 1 protein in myoblast differentiation.

This study was conducted to further understand the mechanism that controls myoblast differentiation, a key step in skeletal muscle formation. RNA sequencing of primary bovine myoblasts revealed many genes encoding the ubiquitin-proteasome system were up-regulated during myoblast differentiation. This up-regulation was accompanied by increased proteasomal activity. Treating myoblasts with the proteasome-specific inhibitor lactacystin impeded myoblast differentiation. Adenovirus-mediated overexpression of inhibitor of DNA binding 1 (ID1) protein inhibited myoblast differentiation too. Further experiments were conducted to determine whether the proteasome promotes myoblast differentiation by degrading ID1 protein. Both ID1 protein and mRNA expression decreased during myoblast differentiation. However, treating myoblasts with lactacystin reversed the decrease in ID1 protein but not in ID1 mRNA expression. Surprisingly, this reversal was not observed when myoblasts were also treated with the mRNA translation inhibitor cycloheximide. Direct incubation of ID1 protein with proteasomes from myoblasts did not show differentiation stage-associated degradation of ID1 protein. Furthermore, ubiquitinated ID1 protein was not detected in lactacystin-treated myoblasts. Overall, the results of this study suggest that, during myoblast differentiation, the proteasomal activity is up-regulated to further myoblast differentiation and that the increased proteasomal activity improves myoblast differentiation partly by inhibiting the synthesis, not the degradation, of ID1 protein.-Leng, X., Ji, X., Hou, Y., Settlage, R., Jiang, H. Roles of the proteasome and inhibitor of DNA binding 1 protein in myoblast differentiation.

Multiple alternative splicing and differential expression patterns of the glycogen synthase kinase-3ß (GSK3ß) gene in Schizothorax prenanti.

Glycogen synthase kinase-3 (GSK-3) is a key protein kinase involved in numerous cellular processes, including embryonic development, protein synthesis, glycogen metabolism, mitosis and apoptosis. However, our knowledge of Schizothorax prenanti GSK-3 is very limited. In this study, we cloned and characterized the S. prenanti GSK3ß gene. Using qPCR, we found that the GSK3ß gene was widely expressed in eleven tissues of S. prenanti and had especially high expression levels in the liver and brain. Moreover, we screened and sequenced more than 100 positive clones to identify the alternative transcripts of GSK3ß. Five novel isoforms of GSK3ß were identified in different S. prenanti tissues; these were different from the GSK3ß isoforms previously reported in the other species. We named the five transcripts as GSK3ß1, GSK3ß2, GSK3ß3, GSK3ß4 and GSK3ß5. These consisted of 1266, 1153, 902, 836 and 654 base pairs, respectively. Our studies provide useful information for further research on the S. prenanti GSK3ß gene.

Multiple alternative splicing and differential expression pattern of the glycogen synthase kinase-3ß (GSK3ß) gene in goat (Capra hircus).

Glycogen synthase kinase-3ß (GSK3ß) has been identified as a key protein kinase involved in several signaling pathways, such as Wnt, IGF-Ι and Hedgehog. However, knowledge regarding GSK3ß in the goat is limited. In this study, we cloned and characterized the goat GSK3ß gene. Six novel GSK3ß transcripts were identified in different tissues and designated as GSK3ß1, 2, 3, 4, 5 and 6. RT-PCR was used to further determine whether the six GSK3ß transcripts existed in different goat tissues. Bioinformatics analysis revealed that the catalytic domain (S_TKc domain) is missing from GSK3ß2 and GSK3ß4. GSK3ß3 and GSK3ß6 do not contain the negative regulatory sites that are controlled by p38 MAPK. Furthermore, qRT-PCR and western blot analysis revealed that all the GSK3ß transcripts were expressed at the highest level in the heart, whereas their expression levels in the liver, spleen, kidney, brain, longissimus dorsi muscle and uterus were different. These studies provide useful information for further research on the functions of GSK3ß isoforms.

Molecular characterization and expression patterns of the actinin-associated LIM protein (ALP) subfamily genes in porcine skeletal muscle.

The actinin-associated LIM protein (ALP) subfamily has important functions in cell signal transduction, cell proliferation, and integration of cytoskeletal architecture. To detect their functions in pig skeletal muscle, we cloned and characterized the pig ALP subfamily genes, drew their genomic structure maps, and detected their tissue expression patterns. We identified a new spliced variant of PDLIM3 in pig skeletal muscle and named it as PDLIM3-4, which was only expressed in the heart and skeletal muscle. Our results showed that PDLIM3-4 was expressed in adult pig skeletal muscle with the highest expression level, and both PDLIM3-4 isoform and PDLIM4 had different expression profiles during the prenatal and postnatal stages of skeletal muscle development among the three pig breeds. These studies provide useful information for further research on the functions of pig ALP subfamily genes in skeletal muscle development.