"Dynamics of myosin heavy chain gene regulation in slow skeletal muscle: Role of natural antisense RNA".

Clay E. Pandorf, Fadia Haddad, Roland R. Roy, Anqi X. Qin, V. Reggie Edgerton, and Kenneth M. Baldwin

Department of Physiology and Biophysics, University of California, Irvine, Irvine, CA 92697

Corresponding Author: cpandorf@uci.edu

Abstract:

The evolutionarily conserved skeletal muscle myosin heavy chain (MHC) genes’ order and close tandem proximity on the same chromosome is intriguing and may be important for their coordinated regulation. We investigated type II MHC gene regulation in slow-type muscle fibers undergoing a slow to fast MHC transformation in response to inactivity, seven days after spinal cord isolation (SI) in rats. We examined the transcriptional products of both the sense and antisense strands across the IIa-IIx-IIb MHC gene locus. A strand-specific RT-PCR approach was utilized to study the expression of the mRNA, the primary transcript (pre-mRNA), the antisense RNA overlapping the MHC genes, and both the intergenic sense and antisense RNAs. Results show that each MHC’s mRNA and pre-mRNA have a similar response to SI, suggesting regulation of these genes at the transcriptional level. In addition, we detected previously unknown antisense strand transcription that produced natural antisense transcripts (NATs). RT-PCR mapping of the RNA products revealed that the antisense activity resulted in the formation of three major products: aII, xII, and bII NATs, antisense products of the IIa, IIx, and IIb genes, respectively. The aII NAT begins in the IIa-IIx intergenic region, in close proximity to the IIx promoter, extends across the 27 kb IIa MHC gene, and continues to the IIa MHC gene promoter. The expression of the aII NAT was significantly upregulated in muscles after SI, was negatively correlated with IIa MHC gene expression, and was positively correlated with IIx MHC gene expression. The exact role of the aII NAT is not clear; however, it is consistent with the inhibition of IIa MHC gene transcription. In conclusion, NATs may mediate crosstalk between adjacent genes, which may be essential to the coordinated regulation of the skeletal muscle MHC genes during dynamic phenotype shifts.

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