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First published online August 3, 2006
Journal of Experimental Biology 209, 3209-3218 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02365

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Decreased expression of myogenic transcription factors and myosin heavy chains in Caenorhabditis elegans muscles developed during spaceflight

Akira Higashibata^1,*, Nathaniel J. Szewczyk^2,, Catharine A. Conley², Mari Imamizo-Sato³, Atsushi Higashitani⁴ and Noriaki Ishioka¹

¹ Japan Aerospace Exploration Agency, 2-1-1, Sengen, Tsukuba, Ibaraki 305-8505, Japan
² Ames Research Center, National Aeronautics and Space Administration, M/S 239-11, Moffett Field, CA 94035-1000, USA
³ Advanced Engineering Services Co. Ltd., Tsukuba Mitsui Building, 1-6-1, Takezono, Tsukuba, Ibaraki 305-0032, Japan
⁴ Graduate School of Life Sciences, Tohoku University, Sendai 980-8577, Japan

View larger version (29K): [in a new window]   Fig. 1. Scatter plot of gene expression by DNA microarray analysis. The whole gene expression profile is plotted as gray spots. Squares and triangles indicate muscle-related genes and their transcription factors, respectively. The closed squares indicate significantly lower expression in response to spaceflight. These groups include myosin heavy chain (MHC) isoforms, troponins and tropomyosins whereas the open squares include actins and non-muscle myosins.

View larger version (16K): [in a new window]   Fig. 2. Real-time quantitative PCR analysis of myosin heavy chain (MHC)-related genes in space flown worms. Expression levels of MHCs (myo-1, -2, -3 and unc-54), paramyosin (unc-15), transcription factors (hlh-1, pha-4, peb-1, ceh-22) and actin (act-3) are shown. The mRNA levels of each gene were adjusted to that of GAPDH (gpd-2) mRNA, which was used as the internal standard. All MHC-related genes decreased in the space-flown worms. Actin levels remained unchanged in response to spaceflight. A summary of the PCR and DNA microarray values is shown in Table 2. Values in the column of real-time PCR are means ± s.e.m. (P<0.05). F, space-flown worms; G, ground controls.

View larger version (16K): [in a new window]   Fig. 3. (A) Western blot analysis of myosin heavy chains (MHCs) and paramyosin. MHC B and C were detected by anti-MHC B and C mouse monoclonal antibody (5-12), and paramyosin was detected by anti-paramyosin rabbit polyclonal antibody (R224). The protein product of gpd-2, GAPDH, was again employed as an internal standard, but the measured levels are not adjusted relative to the standard. Both MHCs and paramyosin in the flight worms show a 10% decrease in the steady-state protein levels compared to that of the ground control worms (B). The table in A summarizes the expression level. Values are means ± s.e.m. (P<0.05).

View larger version (22K): [in a new window]   Fig. 4. Model for downregulation of myosin heavy chain (MHC) gene expression in space. This downregulation is due to a reduction in the level of transcripts encoding the transcription factors that regulate body-wall and pharyngeal MHC expression. Gene expression is influenced by microgravity at the level of transcription, independent of the differences between MHC isoforms and these transcription factors in tissue expression and function.