Poster abstracts

Poster number 83 submitted by Bing Zhang

Mechanistic analysis of reprogramming muscle precursor cells into a neuronal fate by a large non-coding RNA

Bing Zhang (RNA Center, CWRU), Fereshteh Kenari, (RNA Center, CWRU), Saba Valadkhan (RNA Center, CWRU)

Abstract:
The results of the ENCODE project suggest that while over 93% of the human genome is transcribed into RNA, ORFs and their associated UTRs occupy only 2% of the genome (Birney et al., 2007; Mattick, 2007). Interestingly, the percentage of non-coding to protein-coding genomic sequences is much greater in higher eukaryotes compared to simpler organisms, suggesting that the non-coding sequences might be involved in the evolution of complexity (Taft et al., 2007). It is estimated that human genome contains over 70,000 large non-protein coding transcripts (lncRNAs); however, the functional mechanism of this novel class of cellular regulators is almost completely unknown. We have analyzed BORG RNA, a 2766 nucleotide long transcript originally discovered in mouse myoblasts which have been shown to contain no protein-coding capability (Takeda et al., 1998). BORG contains five repeat elements and a region that is ~65% conserved from mouse to human. We have shown that BORG is highly expressed in neural tissues in mouse, as well as in primary cultured neurons, but not astrocytes or oligodendrocytes. We made stable cell C2C12 lines overexpressing full-length BORG and induced muscle differentiation to determine if BORG overexpression affects their ability to differentiate. Surprisingly, the cells developed round cell bodies and long branched processes that interconnected to form a network, features characteristic of neuronal cells. Both immunostaining and RT-PCR data show that the BORG overexpression cells express different neuronal markers in a timely regulated way along their neuronal differentiation. To further characterize the mechanism of this neuronal differentiation, we made different truncation mutations of BORG by deleting the repeat elements one at a time, and overexpressing the truncated RNAs in C2C12 cells. Interestingly, some mutants totally lost the ability of neuronal differentiation while others could still differentiate. This study is a first step toward characterizing the mechanism by which a large non-coding RNA can reprogram muscle precursor cells, which are of mesodermal origin, to neuronal cells, which are of ectodermal origin. Taken together, our study provides an example of the crucial, and hitherto unknown, roles played by non-coding RNAs in regulation of cellular function and development.

Keywords: repeat elements, large non-protein-coding RNA, lncRNA