Insertional mutagenesis in ChordinA induced by endogenous ΔTgf2 transposon leads to bifurcation of axial skeletal systems in grass goldfish.

The grass goldfish appeared early in the evolutionary history of goldfish, and shows heritable stability in the development of the caudal fin. The twin-tail phenotype is extremely rare, however, some twin-tail individuals were produced in the process of breeding for ornamental value. From mutations in the twin-tail goldfish genome, we identified two kinds of Tgf2 transposons. One type was completely sequenced Tgf2 and the other type was ΔTgf2, which had 858 bp missing. We speculate that the bifurcation of the axial skeletal system in goldfish may be caused by an endogenous ΔTgf2 insertion mutation in Chordin A, as ΔTgf2 has no transposition activity and blocks the expression of Chordin A. The twin-tail showed doubled caudal fin and accumulation of red blood cells in the tail. In addition, in situ hybridization revealed that ventral embryonic tissue markers (eve1, sizzled, and bmp4) were more widely and strongly expressed in the twin-tail than in the wild-type embryos during the gastrula stage, and bmp4 showed bifurcated expression patterns in the posterior region of the twin-tail embryos. These results provide new insights into the artificial breeding of genetically stable twin-tail grass goldfish families.

Identification of duplicated Midkine genes and their functional regulation in blunt snout bream (Megalobrama amblycephala).

Midkine (Mdk) is a heparin-binding growth factor that is involved in regulating cell growth, differentiation and migration. Here, we report the isolation and characterization of duplicated mdk genes in blunt snout bream (Megalobrama amblycephala). The mdka and -b genes encode 146 aa and 147 aa peptides, respectively, sharing a sequence identity of 64%. During embryogenesis, mdka mRNA is detectable after 12 h post-fertilization (hpf) and mdkb mRNA can be detected after 8 hpf, about 4 h prior to mdka mRNA. Whole-mount in situ hybridization demonstrated that two paralogs of mdk mRNA were detected in the brain and dorsal neural tube at 16 hpf. At 22 hpf, mdka mRNA was abundant in the brain and dorsal neural tube, whereas mdkb mRNA were transcribed in the brain and tailbud. Later, at 55 hpf, both paralogs were mainly expressed in the brain. Furthermore, both the mdk genes were highly expressed in multiple adult tissues except in the skin and a low expression of mdka in the muscle. In addition, they were differentially inhibited in the liver and intestine with exogenous recombinant human growth hormone, while their mRNA levels were up-regulated in the brain. During starvation, both the mdk genes were significantly up-regulated in the intestine, brain and liver and returned to the control levels following 6 days of refeeding. Our results suggest that duplicated mdk genes may play conserved and divergent roles in embryonic development and tissue growth regulation in blunt snout bream.