Alternative splicing of an rnp-4f mRNA isoform retaining an evolutionarily-conserved 5'-UTR intronic element is developmentally regulated and shown via RNAi to be essential for normal central nervous system development in Drosophila melanogaster.

Two major mRNA isoforms arise via alternative splicing in the 5'-UTR of Drosophila splicing assembly factor rnp-4f pre-mRNA, designated "long" (unspliced) and "short" (alternatively spliced). The coding potential for the two isoforms is identical, raising interesting questions as to the control mechanism and functional significance of this 5'-UTR intronic splicing decision. Developmental Northerns show that two temporally distinct rnp-4f mRNA degradation episodes occur during embryogenesis.