Abstract:
Gene duplication is a major genetic event that can produce multiple protein isoforms. Comparative
sequence and functional analysis of related gene products can provide insights into protein family
evolution. To characterize the Caenorhabditis elegans troponin I family, we analyzed gene structures,
tissue expression patterns and RNAi phenotypes of four troponin I isoforms. Tissue expression
patterns were determined using lacZ/gfp/rfp reporter gene assays. The tni-1, tni-2/unc-27 and
tni-3 genes, each encoding a troponin I isoform, are uniquely expressed in body wall, vulval and
anal muscles but at different levels; tni-4 was expressed solely in the pharynx. Expressing tni-1 and -2
gene RNAi caused motility defects similar to unc-27 (e155 ) mutant, a tni-2 null allele. The tni-3
RNAi expression produced egg laying defects while the tni-4 RNAi caused arrest at gastrulation.
Overlay analyses were used to assay interactions between the troponin I and two troponin C
isoforms. The three body wall troponin I isoforms interacted with body wall and pharyngeal
troponin C isoforms; TNI-4 interacted only with pharyngeal troponin C. Our results suggest the
body wall genes have evolved following duplication of the pharynx gene and provide important
data about gene duplication and functional differentiation of nematode troponin I isoforms.
