The key role of myostatin b in somatic growth in fishes derived from distant hybridization

The basic mechanism of heterosis has not been systematically and completely characterized.In previous studies,we obtained three economically important fishes that exhibit rapid growth,WR(WCC♀×RCC♂),WR-Ⅱ(WR♀×WCC♂),and WR-Ⅲ(WR-Ⅱ♀×4nAU♂),through distant hybridization.However,the mechanism underlying this rapid growth remains unclear.In this study,we found that WR,WR-Ⅱ,and WR-Ⅲshowed muscle hypertrophy and higher muscle protein and fat contents compared with their parent species(RCC and WCC).Candidate genes responsible for this rapid growth were then obtained through an analysis of 12 muscle transcriptomes.Notably,the mRNA level of mstnb(myostatin b),which is a negative regulator of myogenesis,was significantly reduced in WR,WR-Ⅱ,and WR-Ⅲcompared with the parent species.To verify the function of mstnb,a mstnb-deficient mutant RCC line was generated using the CRISPR-Cas9 technique.The average body weight of mstnb-deficient RCC at 12 months of age was significantly increased by 29.57%compared with that in wild-type siblings.Moreover,the area and number of muscle fibers were significantly increased in mstnb-deficient RCC,indicating hypertrophy and hyperplasia.Furthermore,the muscle protein and fat contents were significantly increased in mstnb-deficient RCC.The molecular regulatory mechanism of mstnb was then revealed by transcription profiling,which showed that genes related to myogenesis(myod,myog,and myf5),protein synthesis(PI3K-AKT-mTOR),and lipogenesis(pparγand fabp3)were highly activated in hybrid fishes and mstnb-deficient RCC.This study revealed that low expression or deficiency of mstnb regulates somatic growth by promoting myogenesis,protein synthesis,and lipogenesis in hybrid fishes and mstnb-deficient RCC,which provides evidence for the molecular mechanism of heterosis via distant hybridization.

Ccdc57 is required for straightening the body axis by regulating ciliary motility in the brain ventricle of zebrafish

Recently,cilia defects have been proposed to contribute to scoliosis.Here,we demonstrate that coiled-coil domain-containing 57(Ccdc57)plays an essential role in straightening the body axis of zebrafish by regulating ciliary beating in the brain ventricle(BV).Zygotic ccdc57(Zccdc57)mutant zebrafish developes scoliosis without significant changes in their bone density and calcification,and the maternal-zygotic ccdc57(MZccdc57)mutant embryos display curved bodies since the long-pec stage.The expression of ccdc57 is enriched in ciliated tissues and immunofluorescence analysis reveals colocalization of Ccdc57-HA with acetylated a-tubulin,implicating it in having a role in ciliary function.Further examination reveals that it is the coordinated cilia beating of multiple cilia bundles(MCB)in the MZccdc57 mutant embryos that is affected at 48 hours post fertilization,when the compromised cerebrospinal fluid flow and curved body axis have already occurred.Either ccdc57 m RNA injection or epinephrine treatment reverses the spinal curvature in MZccdc57 mutant larvae from ventrally curly to straight or even dorsally curly and significantly upregulates urotensin signaling.This study reveals the role of ccdc57 in maintaining coordinated cilia beating of MCB in the BV.

Targeted disruption of tyrosinase causes melanin reduction in Carassius auratus cuvieri and its hybrid progeny

The white crucian carp(Carassius auratus cuvieri,WCC) not only is one of the most economically important fish in Asia,characterized by strong reproductive ability and rapid growth rates,but also represents a good germplasm to produce hybrid progenies with heterosis.Gene knockout technique provides a safe and acceptant way for fish breeding.Achieving gene knockout in WCC and its hybrid progeny will be of great importance for both genetic studies and hybridization breeding.Tyrosinase(TYR) is a key enzyme in melanin synthesis.Depletion of tyr in zebrafish and mice results in mosaic pigmentation or total albinism.Here,we successfully used CRISPR-Cas9 to target tyr in WCC and its hybrid progeny(WR) derived from the cross of WCC(♀) and red crucian carp(Carassius auratus red var.,RCC,♂).The level of TYR protein was significantly reduced in mutant WCC.Both the mutant WCC and the mutant WR showed different degrees of melanin reduction compared with the wild-type sibling control fish,resulting from different mutation efficiency ranging from 60% to 90%.In addition,the transcriptional expression profiles of a series of pivotal pigment synthesis genes,i.e.tyrp1,mitfa,mitfb,dct and sox10,were down-regulated in tyr-CRISPR WCC,which ultimately caused a reduction in melanin synthesis.These results demonstrated that tyr plays a key role in melanin synthesis in WCC and WR,and CRISPR-Cas9 is an effective tool for modifying the genome of economical fish.Furthermore,the tyr-CRISPR models could be valuable in understanding fundamental mechanisms of pigment formation in non-model fish.

Evidence for the paternal mitochondrial DNA in the crucian carp-like fish lineage with hybrid origin

In terms of taxonomic status,common carp(Cyprinus carpio,Cyprininae)and crucian carp(Carassius auratus,Cyprininae)are different species;however,in this study,a newborn homodiploid crucian carp-like fish(2n=100)(2nNCRC)lineage(F1–F3)was established from the interspecific hybridization of female common carp(2n=100)×male blunt snout bream(Megalobrama amblycephala,Cultrinae,2n=48).The phenotypes and genotypes of 2 n NCRC differed from those of its parents but were closely related to those of the existing diploid crucian carp.We further sequenced the whole mitochondrial(mt)genomes of the 2n NCRC lineage from F1 to F3.The paternal mt DNA fragments were stably embedded in the mt-genomes of F1–F3 generations of 2n NCRC to form chimeric DNA fragments.Along with this chimeric process,numerous base sites of F1–F3 generations of 2 n NCRC underwent mutations.Most of these mutation sites were consistent with the existing diploid crucian carp.Moreover,the mt DNA organization and nucleotide composition of 2n NCRC were more similar to those of the existing diploid crucian carp than those of the parents.The inheritable chimeric DNA fragments and mutant loci in the mt-genomes of different generations of 2nNCRC provided important evidence of the mt DNA change process in the newborn lineage derived from hybridization of different species.Our findings demonstrated for the first time that the paternal mt DNA were transmitted into the mt-genomes of homodiploid lineage,which provided new insights into the existence of paternal mt DNA in the mt DNA inheritance.