Progress 06/15/04 to 12/31/05
Outputs
The main objectives of this project were to characterize growth patterns of two closely related fish species exhibiting different responses to growth enhancers, zebrafish and giant danios, and consequently demonstrate their viability as animal models for comparative muscle growth studies. The initial step, which was completed at the Marine Biological Laboratory, in this research was to clone and sequence various growth-related genes from giant danios utilizing gene sequences from the zebrafish genome database. We were successful in cloning, sequencing, and verifying various genes (Myogenin, MyoD, M-cadherin, Mck, MSTN, IGF-I) from both zebrafish and giant danios. We were also able to characterize a novel Gdf11 gene from zebrafish that has potential in regulating muscle growth (Biga et al., 2005 Comp. Biochem. Physiol, B; 141:218-230). To demonstrate early-life growth differences between the species, a larval growth study was conducted. Zebrafish larvae size increased
38.9% compared to 84.2% in giant danios from hatch to 4-wk post-hatch. Interestingly, it took zebrafish larvae 3 weeks to reach the size of 1-wk post-hatch giant danio. Giant danio larvae were larger (P<0.0001) than zebrafish at all time periods measured, except hatching. Total myotome area, mean fiber area, and total epaxial fiber number all exhibited similar relationships with overall larvae length, with a significant positive relationship in giant danio (P<0.01) and no significant relationship in zebrafish. Giant danio total fiber number increased faster than mean fiber area, indicating hyperplastic muscle growth (67% of muscle growth). Hyperplasia accounted for 67% of muscle growth in the giant danio, according to calculations based on total fiber number in relation to calculated overall area. In contrast, in zebrafish larvae, hyperplasia accounts for only 47% of muscle growth. To further investigate the differential growth patterns between giant danio and zebrafish, a 17-week
growth trial was conducted to determine the effects of exogenous growth hormone on overall growth in adult giant danio and zebrafish. Fish growth increased (P<0.0001) 46 and 64% over the entire 17-week trial in both 2- and 1-year old giant danio, respectively. Interestingly, both age groups grew at a rate of 0.10g /week, suggesting that regardless of beginning size, giant danios are capable of positively responding to a growth promoting agent. In contrast, female zebrafish only exhibited an increased (P<0.0001) weight following the first injection, while males showed no overall increase (P=0.07) in growth. Collectively, the results of the larval growth study and the adult growth trial suggest that giant danios exhibit indeterminate growth and maintain the ability to respond to a growth promoting agent as adults, while zebrafish adults reach a growth plateau as they mature. This also suggests that the zebrafish and giant danio can be utilized as a direct comparative model system for
muscle growth physiology studies, with the zebrafish serving as a model organism for mammalian-type growth and the giant danio serving as a model for growth in commercially important fish species like rainbow trout.
Impacts
The expected impact of this study includes the validation of a direct comparative muscle growth model system. The results reported from this project demonstrate that the giant danio and zebrafish exhibit different growth patterns, demonstrating their viability as a comparative muscle growth model system. The giant danio exhibits indeterminate growth, consistent with most commercially raised fish species; while the zebrafish exhibits determinate growth that is characteristic of mammalian growth. The expected impact of the validation of the comparative muscle growth model system will allow more in-depth investigations into the control of muscle growth and the anticipated results are two-fold: I) The giant danio can represent commercially important fish species and ultimately lead to novel techniques for enhanced growth, and II) the zebrafish can serve as a model for muscle diseases impacting all vertebrates. Results from this project also demonstrated that research
utilizing the giant danio can take advantage of the available zebrafish genomic resources. The potential impact of these findings include the utilization of the giant danio, on a genomic research level, in physiology studies where the small size of the zebrafish is limiting. This impact has the potential of spanning all areas of physiology, not only muscle growth.
Publications
- Biga, P.R., Roberts S.R., Iliev D.B., McCauley L.A.R., and Goetz F.W. 2005. The isolation, characterization, and expression of a novel GDF11 gene and a second myostatin form in zebrafish, Danio rerio. Comp Biochem Phys. B. 141:218-230.
- Biga, P.R. and F. W. Goetz. 2006. Direct comparison of zebrafish and giant danio as model organisms for muscle growth: I. Determinate versus indeterminate growth as determined by morphometric analysis. Amer. J. Physiol.: Reg., Int., Comp. Physiol. In Review.
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