Actin Gene Expression in the Developing Sea Urchin (Development, Kinetic Model).

Abstract

The sea urchin, Strongylocentrotus purpuratus, contains two sizes of actin messenger RNA (1.8 and 2.2 kb) that are expressed in different amounts during the first 48 hours of development. The 1.8 kb actin message is selectively expressed in the ectoderm of the 72 hour embryo, while the 2.2 kb RNA is selectively expressed in the endoderm/mesoderm. These two actin messenger RNAs code for actins indistinquishable by two-dimensional electrophoresis: however, differences in the actins were identified by tryptic peptide analysis using high pressure liquid chromatography. We have not determined if these differences are phsysiologically significant. To assist in the study of gene expression in this developmental system, we have constructed a kinetic model which considers the changes in the number of cells per embryo and the overall rate of transcription. We have applied this kinetic model to the accumulation of actin messenger RNA which occurs early in sea urchin embryogenesis. This analysis demonstrates that the rapid increase in cell number profoundly influences the kinetics of mRNA accumulation, and that failure to take into account the work performed by each cell can lead to significant misinterpretations of data on the expression of specific genes.