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First published online November 14, 2008
Journal of Experimental Biology 211, 3653-3660 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.023903

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Weight and nutrition affect pre-mRNA splicing of a muscle gene associated with performance, energetics and life history

James H. Marden^1,*, Howard W. Fescemyer¹, Marjo Saastamoinen², Suzanne P. MacFarland¹, J. Cristobal Vera¹, Mikko J. Frilander³ and Ilkka Hanski²

¹ Department of Biology, 208 Mueller Laboratory, Pennsylvania State University, University Park, PA 16802, USA
² Department of Biological and Environmental Sciences, University of Helsinki, Viikinkaari 1, PL 65, 00014 Helsinki, Finland
³ Institute of Biotechnology, University of Helsinki, Viikinkaari 9, PL 56, 00014 Helsinki, Finland

View larger version (43K): [in this window] [in a new window]   Fig. 1. Variable N-terminal region of protein isoforms produced by alternative splicing of the Tnt gene in fall armyworm moths and Glanville fritillary butterflies. Alternative exons are colored. Traces on the right show capillary electrophoresis separation of PCR products generated by primers that hybridize on either side of the alternative exon region and from which we determined fragment size and relative abundance. Fragment size measurements match predicted sizes from sequence data. Red peaks are internal size standards. Inset shows western blot of moth flight muscle protein separated by SDS-PAGE and hybridized with MAC 145 antibody specific to insect Tnt. Relative abundances of Tnt F transcripts from the same individuals (below each lane) show agreement with the Tnt F protein isoforms. Specifically, these data show that Tnt F was the predominant protein form when Tnt F transcript relative abundance was high, and was about half of the protein when Tnt F was about 50% of the transcript pool. (Adult moth photo courtesy of Renn Tumlison.)

View larger version (9K): [in this window] [in a new window]   Fig. 2. Duration of the final larval instar and adult fresh body mass for moths reared in different feeding treatments (N=108). Labels indicate the number of days that larvae were fed prior to removal of food (i.e. F1S were fed 1 day, then starved until pupation) or the number of days starved prior to feeding until pupation (i.e. S4F were starved 4 days, then fed until pupation). Two groups were fed the whole time (F).

View larger version (29K): [in this window] [in a new window]   Fig. 3. Tnt F (means ± s.d.) in flight muscles of groups of moths (N=108) representing different larval feeding treatments (A) and in relation to body mass (B,C). Ratios are arcsine transformed to achieve normality; right axis in B shows the scale of untransformed relative abundances. Labels in A indicate the number of days fed during the final larval stage prior to removal of food or the number of days starved prior to feeding until pupation (as in Fig. 2). C shows regression lines and the least squares means from a multivariate model with body mass and feeding treatment (no significant interaction). (D) Peak flight metabolic rate in relation to relative abundance of Tnt F in female moths.

View larger version (21K): [in this window] [in a new window]   Fig. 4. Relative abundances of the six isoforms of Tnt in the fall armyworm moth in relation to total mass (body+added load) and larval feeding treatment (fully fed versus fed 2 days then starved). Lines in the large plot show individual regressions for each of the four treatment groups for the most abundant isoform, Tnt F. Smaller plots show effects of total mass (solid lines) or nutrition (dashed lines for Tnt D at total mass >100 mg) in the remaining five isoforms.

View larger version (9K): [in this window] [in a new window]   Fig. 5. Relative abundance of Tnt F in fall armyworm moths as a function of total mass (body+added load). Superimposed on the plot are gray points showing the unladen body mass of the weight-manipulated individuals, with horizontal lines connecting their unladen mass to their total mass after attachment of a weight load. The vertical distance from the fitted line to the gray points is the difference between the observed and predicted Tnt F relative abundance if there had been no adjustment of Tnt F to the added weight. The reduced unladen body mass of the fully fed weight-loaded moths was presumably caused by the increased cost of activity over 5 days while weight loaded or by active reduction in body mass, or both.

View larger version (7K): [in this window] [in a new window]   Fig. 6. Relative abundance of Tnt A in the flight muscles of Glanville fritillary female butterflies in relation to (A) the number of times per day butterflies were observed perching with open wings (basking; thermoregulation in preparation for flight) and (B) the rate of reproduction (number of eggs laid per day). The relationships in A and B both show statistical significance that is independent of initial body mass.

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