Towards the Ictalurid Catfish Transcriptome: Generation and Analysis of 31,215 Catfish ESTs.

Background EST sequencing is one of the most efficient means for gene discovery and molecular marker development, and can be additionally utilized in both comparative genome analysis and evaluation of gene duplications. While much progress has been made in catfish genomics, large-scale EST resources have been lacking. The objectives of this project were to construct primary cDNA libraries, to conduct initial EST sequencing to generate catfish EST resources, and to obtain baseline information about highly expressed genes in various catfish organs to provide a guide for the production of normalized and subtracted cDNA libraries for large-scale transcriptome analysis in catfish. Results A total of 17 cDNA libraries were constructed including 12 from channel catfish (Ictalurus punctatus) and 5 from blue catfish (I. furcatus). A total of 31,215 ESTs, with average length of 778 bp, were generated including 20,451 from the channel catfish and 10,764 from blue catfish. Cluster analysis indicated that 73% of channel catfish and 67% of blue catfish ESTs were unique within the project. Over 53% and 50% of the channel catfish and blue catfish ESTs, respectively, had significant similarities to known genes. All ESTs have been deposited in GenBank. Evaluation of the catfish EST resources demonstrated their potential for molecular marker development, comparative genome analysis, and evaluation of ancient and recent gene duplications. Subtraction of abundantly expressed genes in a variety of catfish tissues, identified here, will allow the production of low-redundancy libraries for in-depth sequencing. Conclusion The sequencing of 31,215 ESTs from channel catfish and blue catfish has significantly increased the EST resources in catfish. The EST resources should provide the potential for microarray development, polymorphic marker identification, mapping, and comparative genome analysis

Assembly of 500,000 inter-specific catfish expressed sequence tags and large scale gene-associated marker development for whole genome association studies

Twelve cDNA libraries from two species of catfish have been sequenced, resulting in the generation of nearly 500,000 ESTs

Monosex female production in the silver barb (Puntius gonionotus Bleeker)

This paper describes hormonal masculinisation of genetically female, gynogenetic silver barbs (Puntius gonionotus) and the results of crosses between such neomales and ordinary females. Gynogenetic fish (previously shown to be all females) were used in trials on hormonal masculinisation to simplify assessment of the results. Treatment with 25 mg kg-1 17α-methyltestosterone in the diet for 4 or 5 weeks, starting at two weeks post-hatch, produced 33.9% and 29.8% males, respectively. The majority of crosses between such males and ordinary females gave all-female progeny, which supports the hypothesis of female homogamety and establishes that large-scale production of monosex females is feasible in this species. A growth trial comparing monosex female groups to mixed-sex groups in pond culture showed an increase in yield from the monosex groups. The implications of the results for commercial production of monosex female silver barbs are discussed

Construction of Genetic Linkage Maps and Comparative Genome Analysis of Catfish Using Gene-Associated Markers

A genetic linkage map of the channel catfish genome (N = 29) was constructed using EST-based microsatellite and single nucleotide polymorphism (SNP) markers in an interspecific reference family. A total of 413 microsatellites and 125 SNP markers were polymorphic in the reference family. Linkage analysis using JoinMap 4.0 allowed mapping of 331 markers (259 microsatellites and 72 SNPs) to 29 linkage groups. Each linkage group contained 3–18 markers. The largest linkage group contained 18 markers and spanned 131.2 cM, while the smallest linkage group contained 14 markers and spanned only 7.9 cM. The linkage map covered a genetic distance of 1811 cM with an average marker interval of 6.0 cM. Sex-specific maps were also constructed; the recombination rate for females was 1.6 times higher than that for males. Putative conserved syntenies between catfish and zebrafish, medaka, and Tetraodon were established, but the overall levels of genome rearrangements were high among the teleost genomes. This study represents a first-generation linkage map constructed by using EST-derived microsatellites and SNPs, laying a framework for large-scale comparative genome analysis in catfish. The conserved syntenies identified here between the catfish and the three model fish species should facilitate structural genome analysis and evolutionary studies, but more importantly should facilitate functional inference of catfish genes. Given that determination of gene functions is difficult in nonmodel species such as catfish, functional genome analysis will have to rely heavily on the establishment of orthologies from model species

Selected examples of the ability to differentiate between catfish allelic variants and gene duplicates (paralogues) using both blue catfish and channel catfish sequences

<p><b>Copyright information:</b></p><p>Taken from "Towards the ictalurid catfish transcriptome: generation and analysis of 31,215 catfish ESTs"</p><p>http://www.biomedcentral.com/1471-2164/8/177</p><p>BMC Genomics 2007;8():177-177.</p><p>Published online 18 Jun 2007</p><p>PMCID:PMC1906771.</p><p></p> Highly similar channel catfish sequences (Channel) and at least one blue catfish sequence (Blue) sharing the same BLAST identity were subjected to phylogenetic analysis. The topological stability of the neighbor joining trees was evaluated by 1000 bootstrapping replications, and the bootstrapping values are indicated by numbers at the nodes. Channel catfish and blue catfish genes placed into the same clade indicate that the additional, related channel catfish sequence is likely a paralogue rather than an allelic variant