Cymric, a Maternal and Zygotic HTK-16-Like SHARK Family Tyrosine Kinase Gene, Is Disrupted in Molgula occulta, a Tailless Ascidian.

Abstract

AbstractWe describe the cloning and expression of a nonreceptor tyrosine kinase, cymric (Uro-1), a HTK-16-like (HydraTyrosineKinase-16) gene, identified in a subtractive screen for maternal ascidian cDNAs in Molgula oculata, an ascidian species with a tadpole larva. The cymric gene encodes a 4-kb mRNA expressed in gonads, eggs, and embryos in the tailed M. oculata but is not detected in eggs or embryos of the closely related tailless species Molgula occulta. There is a large insertion in cymric in the M. occulta genome, as shown by transcriptome and genome analyses, resulting in it becoming a pseudogene. The cymric amino acid sequence encodes a nonreceptor tyrosine kinase with an N-terminal region containing two SH2 domains and five ankyrin repeats, similar to the HTK-16-like gene found in other ascidians. Thus, the ascidian cymric genes are members of the SHARK (Src-homology ankyrin-repeat containing tyrosine kinase) family of nonreceptor tyrosine kinases, which are found throughout invertebrates and missing from vertebrates. We show that cymric is lacking the tyrosine kinase domain in the tailless M. occulta, although the truncated mRNA is still expressed in transcriptome data. This maternal and zygotic HTK-16-like tyrosine kinase is another described pseudogene from M. occulta and appears not to be necessary for adult development.