Dramatically accelerated growth and extraordinary gigantism of transgenic mud loach Misgurnus mizolepis

Transgenic mud loaches (Misgurnus mizolepis), in which the entire transgene originated from the same species, have been generated by microinjecting the mud loach growth hormone (mlGH) gene fused to the mud loach beta-actin promoter. Out of 4,100 eggs injected, 7.5% fish derived from the injected eggs showed dramatically accelerated growth, with a maximum of 35-fold faster growth than their non-transgenic siblings. Many fast-growing transgenic individuals showed extraordinary gigantism: their body weight and total length (largest fish attained to 413 g and 41.5 cm) were larger and longer than even those of 12-year-old normal broodstock (maximum size reached to 89 g and 28 cm). Of 46 transgenic founders tested, 30 individuals transmitted the transgene to next generation with a wide range of germ-line transmission frequencies ranging from 2% to 33%. The growth performance of the subsequent generation (F1) was also dramatically accelerated up to 35-fold, although the levels of enhanced growth were variable among transgenic lines. Three transgenic germ-lines up to F4 were established, showing the expected Mendelian inheritance of the transgene. Expression of GH mRNA in many tissues was detected by RT-PCR analyses. The time required to attain marketable size (10 g) in these transgenic lines was only 30-50 days after fertilization, while at least 6 months in non-transgenic fish. Besides growth enhancement, significantly improved feed-conversion efficiency up to 1.9-fold was also observed.

Genomic organization and sequence of the mud loach (Misgurnus mizolepis) growth hormone gene: a comparative analysis of teleost growth hormone genes

The mud loach (Misgurnus mizolepis) growth hormone (GH) gene was cloned and a comparative analysis on its genomic organization was performed. Based on Southern analysis using various kinds of restriction endonucleases, the GH gene proved to exist as a single-copy gene in the mud loach. The complete nucleotide sequences of a 5.1 kb SacI/EcoRI genomic fragment containing the mud loach GH gene and its 5' flanking sequences as well as a mud loach GH cDNA obtained by rapid amplification of a reverse transcriptase-PCR have been determined. The GH gene spans 2.0 kb from the start codon to the polyadenylation signal, and contains five exons and four introns similar to those of carps and mammals. The evolutionary relation of the mud loach GH gene, inferred by comparative analyses of gene structures and sequences in each exon and intron of representative teleost GH genes, reflects the major phylogenetic groupings of teleost.