sentence: Large-scale cDNA sequencing projects in mammals have revealed that eukaryotic cells contain numerous polyadenylated noncoding RNAs ( ncRNAs ) that are expected to play physiological roles , especially in the regulation of gene expression ( Okazaki et al ., 2002 ; Mattick , 2004 ; Carninci et al ., 2005 ; Tomilin , 2008 ) .