Mol. Cell http://dx.doi.org/10.1016/j.molcel.2016.08.010 (2016)

Credit: ELSEVIER

Long non-coding RNAs (lncRNAs) are transcripts of >200 nucleotides known to modulate biological processes by targeting gene regulatory pathways. Yet, because of their limited conservation, low abundance and large size, it remains a challenge to determine the molecular mechanisms of lncRNA action in mammalian cells. Xue et al. now define an RNA motif within the mouse Braveheart (Bvht) lncRNA that is required for its function in regulating cardiomyocyte differentiation. Using in vitro chemical probing of full-length and fragment domains of Bhvt, the authors generated a secondary structure map for the 590-nucleotide Bvht, which features a central five-way junction and an unusual asymmetric G-rich internal loop (AGIL) near the 5′ end of the transcript. Deletion of the AGIL motif within Bvht (dAGIL) by CRISPR/Cas9 genome editing demonstrated that Bvht AGIL is necessary for cardiovascular cell lineage determination. Differential probing of protein microarrays identified proteins—including CNBP, a zinc-finger transcription factor abundant in heart cells—that bind the AGIL motif of Bvht. Knockout studies defined CNBP as a negative regulator of cardiomyocyte development that is antagonistic with dAGIL deletion, supporting a mechanism in which Bvht controls the cardiac cell lineage by selective binding of the negative regulator, CNBP.