Alternative splicing of the Endo16 transcript produces differentially expressed mRNAs during sea urchin gastrulation

Abstract

The Endo16 gene codes for an RGD-containing calcium-binding protein that is found on the basal surfaces and in the extracellular matrix of cells of the invaginating archenteron during sea urchin gastrulation. Previously, we have-shown that Endo16 is a single copy gene and we have determined the coding sequence and analyzed the temporal and spatial expression of a 6.6-kb mRNA. In this report we demonstrate that two additional longer Endo16 mRNAs are produced by differential splicing rather than alternative promoter usage. cDNA clones for two 8.5-kb mRNAs have been isolated and analyzed. The two 8.5-kb mRNAs are identical to each other in the coding region and differ only in their 3' UTRs. The extended open reading frame of the 8.5-kb mRNAs code for domains already identified in the 6.6-kb mRNA, including two different types of calcium-binding motifs and a region with a highly conserved cysteine pattern similar to that found in Ecm1 in the mouse. The 6.6- and 8.5-kb mRNAs show overlapping but distinct temporal as well as spatial expression patterns during gastrulation.