First International C. elegans Experiment (ICE-first). Microgravity effects on the muscle thick filament in the paramyosin mutant of Caenorhabditis elegans

First International C. elegans Experiment (ICE-first). Microgravity effects on the muscle thick filament in the paramyosin mutant of Caenorhabditis elegans

Ryota Adachi, Tomohide Takaya, Kana Kuriyama, Noriaki Ishioka, Hiroaki Kagawa.

Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan.

The 15th International C. elegans Meeting (Los Angels, USA), 2005/06/28 (Talk).

Abstract

A variety of organ systems have been identified major biological changes in microgravity. In vertebrate skeletal muscle, greatest changes are observed in the limb antigravity muscles such as soleus. The conversion of MHC isoforms from slow to fast type is observed. At the molecular level, distinct MHC promoter sequences mediate MHC expression in response to overload and unloading in mice. Caenorhabditis elegans has no fast and slow type isoforms as is seen in vertebrate, but has similar genes or isoforms of muscle proteins. These are four genes of MHCs; two of body wall type and two of pharynx type, single gene of paramyosin; unc-15 expressing in all muscle cells, single gene of tropomyosin; tmy-1/lev-11 encoding four isoforms, two for body wall muscles, and two for pharyngeal and gut muscles by alternative splicing. MHCs and paramyosin are the major components of thick filament. The mutant unc-15(e73) animal form abnormal thick filament by the reason of amino acid substitution of Glu342 to Lys but produce normal level of paramyosin of a same size as that of wild type. To investigate the microgravity effect on C. elegans, we used wild type and the unc-15(e73) animals. In this study, ICE-First, we compared the paramyosin mutant with wild type worm subjected 10 days of microgravity, in spaceflight and ground control groups. Worms were cultivated in the liquid medium, CeMM, during the mission on International Space Station (ISS). Contrast to no significant change of the muscle fiber size in observation under microscopy and the protein quantity of wild type worm in Western analysis by using specific antibody and single worm, the atrophy of body wall muscle and increments of MHCs and paramyosin were observed in the paramyosin mutant unc-15(e73) animals after spaceflight. This indicates that the muscle abnormal mutant responds to microgravity and tends to compensate muscle function increasing muscle protein amount. On the other hand no change of thin filament proteins, actin and tropomyosin was detected by Western analysis even we used thirty worms. This result suggests that possibility of the different control of thick and thin filament proteins has not been clarified in any other experiments done before.