Construction of a genetic linkage map and mapping of a female-specific DNA marker in half-smooth tongue sole (Cynoglossus semilaevis)

The half-smooth tongue sole (Cynoglossus semilaevis, hereafter, "tongue sole") is a marine flatfish with great commercial importance for fisheries and aquaculture in China. It has also been a promising model for the study of sex determination mechanisms in fish. Here, we report the construction of a genetic linkage map for the tongue sole, based on 137 markers including 103 AFLP markers, 33 microsatellite markers, and one female-specific DNA marker. Twenty-six linkage groups (LGs) were found. The total map length was 934.6 cM (Kosambi), with an average spacing of 8.4 cM, covering 64.4% of the estimated genome size. Furthermore, a female-specific SCAR marker, CseF-382, was mapped on LG5. This study represents the first genetic linkage map in the tongue sole. This map has great potential in the identification of quantitative traits loci and sex-related genes and marker-assisted selection in the tongue sole. Meanwhile, the new set of polymorphic microsatellite markers developed in this study is not only useful for genetic mapping but also of critical importance for studies on genetic diversity and broodstock management in tongue sole.

cDNA cloning and expression analysis of thyroid hormone receptor in the coho salmon Oncorhynchus kisutch during smoltification

Two types of cDNA clones encoding thyroid hormone receptor (TR) genes, TRalpha and TRbeta, were isolated from the coho salmon Oncorhynchus kisutch. The two genes each consists of multiple isoforms, derived from different loci or by an alternative splicing. RT-PCR revealed a broad localization of the TRalpha and TRbeta transcripts that both expressed in brain, gill, liver, muscle, kidney, ovary, skin and eyeball. During the early stages of the smoltification period, the mRNA level of the TR transcripts showed a large individual variability at the maximum of 10-fold. In contrast, as the plasma thyroid hormone level elevated at the middle of the period, the variation in the expression level became much smaller at 2-fold. After the completion of the smoltification, the mRNA accumulation level of the TR genes rapidly decreased. These findings suggest that the dynamics of the receptor (TR) should be taken account in addition to the availability of the hormone ligands (T3 and T4) to understand the underlying mechanisms of the smoltification causing numerous physiological and morphological changes in salmonids.