Tissue expression of four troponin I genes and their molecular interactions with two troponin C isoforms in Caenorhabditis elegans

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.

Spaceflight results in increase of thick filament but not thin filament proteins in the paramyosin mutant of Caenorhabditis elegans

“…This suggests that the transcriptional control of C. elegans contractile protein is different from that of mice, and that there are different transcriptional control responses to microgravity for thick and thin filament proteins in C. elegans. Recently we have determined that the unc-27(e155) animal, the null mutant of the major body-wall troponin I gene, produced UNC-27 only 20 % of the wild-type (Ruksana et al, 2005). As there are three body-wall type troponin I genes in the worm, two other troponin I genes can produce the product.…”

C. Elegans Model for Studying Tropomyosin and Troponin Regulations of Muscle Contraction and Animal Behavior

“…The three body wall troponin I isoforms interacts with the body wall and pharyngeal troponin C isoforms, reciprocally, but the pharyngeal TnI-4 interacts only with the pharyngeal TnC-2. Our results suggest that body wall TnI genes have evolved following duplication of the pharynx gene and provide important data about gene duplication and functional differentiation of nematode troponin I isoforms (Ruksana et al, 2005). Recently we confirmed that the N-terminal part of troponin I interacts with troponin C of the worm (Amin and Kagawa, unpublished).…”

“…Isolated mutants of troponin I and troponin T are found only in the abundant body wall isoform genes of tni-2/unc-27 and mup-2/tnt-1, which are expressed in body wall muscles, respectively (Table 1). Some differences of expression control and tissue localization of the three troponin I genes are detected between these three muscle groups, but functional differences have not been found in comparisons of the amino acid sequences (Ruksana et al, 2005). It is of interest to know how three isoforms of troponin I and troponin T interact each other and are utilized in different tissues.…”

“…The N-terminal extension is found in vertebrate cardiac and all invertebrate troponin I isoforms. There is a C-terminal hydrophilic regions in the three troponin I isoforms of C. elegans (Ruksana et al, 2005). This may be important for interactions with other proteins.…”

“…An RNAi experiment for tni-3 produced egg-laying defects, while similar experiment with tni-4 RNAi caused arrest at gastrulation (Table 1). These show that body wall troponin I isoforms are important for animal motility and egg-laying and that the pharynx troponin I is essential for animal development (Ruksana et al, 2005).…”