Analysis of intronless genes involved in oscillation and differentiation

The genomes of higher eukaryotes are replete with intron-containing genes. Transcription of these genes produces precursor mRNAs containing intervening sequences, which are subsequently removed and the exons spliced together to form the mature mRNA. However, a small proportion of eukaryotic protein-coding genes are intronless and therefore bypass post-transcriptional splicing events. Although a large proportion of intronless genes are known to code for certain types of proteins, their specific role in the genome of higher organism is perplexing. This research set out to elucidate the functions of intronless genes in humans by studying their involvement in the expression pattern of oscillatory gene that occurs in the pre-somitic mesoderm of developing embryo. Twenty-seven (27) human homologs of mouse oscillatory genes were analysed to determine the number of exons present in them using various bioinformatics databases. The result obtained identified two intronless genes –NRARP and ID1 – which are associated with the Notch signalling pathway of the segmentation clock. This represented 7.4% of the total oscillatory genes analysed. No intronless gene was found in the Wnt and FGF signalling pathways – two other pathways famous for oscillatory gene expression. The proteins encoded by the intronless genes are involved in several important biological processes including angiogenesis, cell cycle control and in the regulation of cellular senescence. Although oscillatory genes had fewer numbers of introns compared to the non-oscillatory genes, the intronless genes were not implicated in the regulation of the precise timing events of the segmentation clock. This result may also point to the fact that the rapid expression rate of the oscillatory genes in the PSM may favour the reduced intron length of the oscillatory genes.