Genomic organization and neonatal expression of the bovine myostatin gene.

Myostatin belongs to the Transforming Growth Factor-beta (TGF-beta) superfamily and is expressed in developing and mature skeletal muscle. Biologically, the role of myostatin seems to be extremely well conserved during evolution since inactivating mutations in myostatin gene cause similar phenotype of heavy muscling in both mice and cattle. In this report we have analysed the genomic structure and neonatal expression of the bovine myostatin gene. The molecular analysis shows that the bovine myostatin gene consists of three exons and two introns. The sizes of the first and second exons are 506 and 374 base pairs (bp) respectively. The size of the third exon was found to be variable in length (1701 or 1812 or 1887 nucleotides), whereas the size of the two introns is 1840 and 2033 bps. In the first exon of bovine myostatin, a single transcription initiation site is found at 133 bps from the translation start codon ATG. Sequencing the 3' untranslated region indicated that there are multiple polyadenylation signals at 1301, 1401 and 1477 bp downstream from the translation stop codon (TGA). Furthermore, 3' RACE analysis confirmed that all three polyadenylation sites are used in vivo. Using quantitative RT-PCR we have analysed neonatal expression of myostatin gene. In both the M. biceps femoris and M. semitendinosus, the highest level of myostatin expression was observed on day 1 postnatally, then gradually reduced on days 8 and 14 postnatally. In contrast, in the M. gastrocnemius, myostatin expression was highest on day 14 and lowest on day 8. These results indicate that myostatin gene structure and function is well conserved during evolution and that neonatal expression of myostatin in a number of predominantly fast twitch muscles is differentially regulated.

The pebble GTP exchange factor and the control of cytokinesis.

Several G proteins of the Rho family have been shown to be required for cytokinesis. The activity of these proteins is regulated by GTP exchange factors (GEFs), which stimulate GDP/GTP exchange, and by GTPase activating proteins (GAPs), which suppress activity by stimulating the intrinsic GTPase activity. The role of Rho family members during cytokinesis is likely to be determined by their spatial and temporal interactions with these factors. Here we focus on the role of the pebble (pbl) gene of Drosophila melanogaster, a RhoGEF that is required for cytokinesis. We summarise the evidence that the primary target of PBL is Rho1 and describe genetic approaches to elucidating the function of PBL and identifying other components of the PBL-activated Rho signalling pathway.

Myostatin, a transforming growth factor-beta superfamily member, is expressed in heart muscle and is upregulated in cardiomyocytes after infarct.

Myostatin is a secreted growth and differentiating factor (GDF-8) that belongs to the transforming growth factor-beta (TGF-beta) superfamily. Targeted disruption of the myostatin gene in mice and a mutation in the third exon of the myostatin gene in double-muscled Belgian Blue cattle breed result in skeletal muscle hyperplasia. Hence, myostatin has been shown to be involved in the regulation of skeletal muscle mass in both mice and cattle. Previous published reports utilizing Northern hybridization had shown that myostatin expression was seen exclusively in skeletal muscle. A significantly lower level of myostatin mRNA was also reported in adipose tissue. Using a sensitive reverse transcription-polymerase chain reaction (RT-PCR) technique and Western blotting with anti-myostatin antibodies, we show that myostatin mRNA and protein are not restricted to skeletal muscle. We also show that myostatin expression is detected in the muscle of both fetal and adult hearts. Sequence analysis reveals that the Belgian Blue heart myostatin cDNA sequence contains an 11 nucleotide deletion in the third exon that causes a frameshift that eliminates virtually all of the mature, active region of the protein. Anti-myostatin immunostaining on heart sections also demonstrates that myostatin protein is localized in Purkinje fibers and cardiomyocytes in heart tissue. Furthermore, following myocardial infarction, myostatin expression is upregulated in the cardiomyocytes surrounding the infarct area. Given that myostatin is expressed in fetal and adult hearts and that myostatin expression is upregulated in cardiomyocytes after the infarction, myostatin could play an important role in cardiac development and physiology.