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Red carp and red crucian carp are ornamental fish with a red body color. Unlike in red crucian carp, no melanophores are observed in red carp embryos or larvae. To explore the roles of the mitfa gene in body color formation in red carp, we investigated the structural characteristics and physicochemical properties of the mitfa gene in 16 kinds of fish. The mitfa amino acid sequence similarity between red carp and red crucian carp was 95.6%, and this was 91.5% similar between carp and zebrafish. Compared with red crucian carp, red carp showed lower tyrp1 messenger ribonucleic acid (mRNA) expression but similar mitfa mRNA expression in the body pigment stage of the embryo. Moreover, mitfa+ cells as well as melanocytes could be observed in cultured embryo cells derived from red carp and red crucian carp. Our data show that the absence of melanophores in red carp is not the result of mitfa gene deletion or mutation, increasing our understanding of the molecular and genetic mechanisms of coloration in cyprinid fish. [ABSTRACT FROM AUTHOR]

Melanocyte stem cells are a population of immature cells which sustain the self-renewal and replenish the differentiated melanocytes. In this research, a light-colored region (LCR) is observed at the heel of caudal fin in juvenile crucian carp. By cutting off the caudal fin, the operated caudal fin can regenerate in accordance with the original pigment pattern from the retained LCR. As markers of stem cells, Oct4 and Sox2 have been found to be highly expressed in the LCR as well as Mitfa, a label of the melanoblasts. In vitro, Mitfa+ melanoblasts are observed in the cells which are derived from the LCR and transfected with Mitfa-EGFP reporter by using Tol2 transposon system. Furthermore, by real-time qPCR, it is shown that the level of sox2 mRNA is gradually decreased from the LCR to proximal and distal caudal fin, and that of mitfa mRNA in the proximal caudal fin (PCF) is higher than that in the LCR, while it is the lowest in the distal caudal fin. Hence, we propose that the LCR is a pigment progenitor niche, sending melanocytes to the distal of caudal fin, which gradually emerges as caudal fin grow. We reveal that the LCR of caudal fin might be a niche of pigment progenitors, and contribute to pigment-producing stem cells in crucian carp. [ABSTRACT FROM AUTHOR]

Background: Reference genes are usually stably expressed in various cells and tissues. However, it was reported that the expression of some reference genes may be distinct in different species. In this study, we intend to answer whether the expression of reported traditional reference genes changes or not in the polyploid fish Results: By retrieving the mRNA sequencing data of three different ploidy fish from the NCBI SRA database, we selected 12 candidate reference genes, and examined their expression levels in the 10 tissues and in the four cell lines of three different ploidy fish by real-time PCR. Then, the expression profiles of these 12 candidate reference genes were systematically evaluated by using the software platforms: BestKeeper, NormFinder and geNorm. Conclusion: The 28S ribosomal protein S5 gene (RPS5) and the ribosomal protein S18 gene (RPS18) are the most suitable reference genes for the polyploid of Cyprinus carpio and Carassius auratus, demonstrated by both of the tissues and the cultured cells. [ABSTRACT FROM AUTHOR]

Color pattern is one of the most important characteristics of species, which plays essential roles in reproduction, adaptability, and even survival. The adult caudal fin of common carp (Cyprinus carpio) has an asymmetrical distribution of body color, with the dorsal lobe (DL) being dark-gray and the ventral lobe (VL) being red. This study first investigates the cytological basis of forming such an asymmetric distribution by observing the component of pigment cells and exploring the early development of the body color, combined with adult caudal fin regeneration experiments in the common carp. In terms of the distribution feature and the number of pigment cells, differences between the DL and the VL are demonstrated, especially with respect to their erythrophores. Abundant lipid droplets and carotenoid droplets are observed in the VL, conforming to the distribution of erythrophores. Analysis of the gene expression profiles indicates that there are highly expressed levels of carotenoid deposition and lipid droplets transport genes, such as scarb and plin6. In contrast, the gene expression levels of the β-carotene dioxygenase (bco) family are significantly down-regulated in the VL. In addition, knocking down of the bco2a gene expression level causes a significant increment of erythrophores. It is concluded that the directed accumulation of lipid droplets and carotenoid particles is the reason for the asymmetric distribution of red color in the caudal fin of common carp. • Erythrophores determine the asymmetric colors of caudal fin in common carp. • Erythrophores distribution depends on carotenoid particles and lipid droplets. • Screened bco2a gene is a functional gene of erythrophore formation. [ABSTRACT FROM AUTHOR]