Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 9/15/2006
Publication Date: 11/3/2006
Citation: Nichols, K., Broman, K., Gahr, S.A., Rexroad III, C.E., Sundin, K., Young, J., Phillips, R., Wheeler, P., Thorgaard, G. 2006. The genetic architecture of development rate in rainbow trout: QTL, QTL x maternal environment, and candidate gene expression. [abstract]. 4th Ecological Genomics Symposium.
Technical Abstract: Embryonic development rate is associated with optimal emergence timing in salmonid fishes, and has important implications for the survivability and performance of juveniles as they emerge from the gravel for feeding. Furthermore, embryonic development rate has been associated with both juvenile growth performance and adult age at sexual maturity. We have identified a major embryonic development rate quantitative trait locus (QTL), accounting for greater than 20% of the variation in this trait, in line crosses of rainbow and steelhead trout (Oncorhynchus mykiss). We tested whether this and other detected QTL exhibit significantly different additive effects in different maternal cytoplasmic environments, and have begun to identify candidate genes and their expression in this region. For QTL mapping, doubled haploid mapping progeny were produced by androgenesis using eggs from nine different females (or maternal cytoplasmic environments). Line crosses used include an Oregon State University (OSU) female Shasta-type rainbow trout line crossed with the Clearwater River (CW) steelhead. Briefly, unfertilized eggs were irradiated to destroy the maternal nuclear DNA component, and then fertilized with sperm from one OSU x CW F1 individual. After fertilization, diploidy is restored by preventing the first embryonic cleavage. Time from fertilization to hatch was recorded for each individual reared in a constant 11 deg C environment. Six QTL were associated with development rate, and both maternal cytoplasmic environment (MCE) and QTL x MCE significantly contributed to variation in development rate. Additive effects of the major QTL, tth-OC-8a, were not significantly different among MCE, but some minor effect QTL (tth-OC-b and tth-OC-9) did exhibit significant QTL x MCE. In a separate study to identify candidate genes in the region of the major development rate QTL, we have mapped two genes in the region and followed the expression of these genes during embryonic development. These genes, growth hormone receptor (GHR) and a negative growth and differentiation gene (GADD45-beta) are duplicated, and one duplicate maps to the region of the development rate QTL. Embryonic expression of the duplicates is quite different early in development for GADD45-beta, but very similar for GHR. Additional fine mapping, molecular evolution, and expression analyses are underway to further define the identity of and variation within genes functionally associated with this trait. This QTL region is also associated with spawn timing in rainbow trout, and shows greatly reduced recombination rates in both male and female maps. Further dissection of this region can have important implications in understanding the genetic and evolutionary mechanisms regulating life history differences within O. mykiss.