The four dimensions of noncoding RNA conservation.

Evolutionary conservation is widely used as an indicator of the functional significance of newly discovered genes. Although the simple search for homology at the nucleotide or amino acid sequence level has proven to be valuable for protein-coding genes, these criteria are too narrow to describe fully the selection process for long noncoding RNAs (lncRNAs). LncRNA conservation includes four dimensions: the sequence, structure, function, and expression from syntenic loci. Two recently described knockout mouse models for the lincRNAs metastasis associated lung adenocarcinoma transcript 1 (Malat1) and HOX antisense intergenic RNA (Hotair) highlight the multifaceted levels of conservation.