Metabolome and Transcriptome Analysis of Liver and Oocytes of Schizothorax o'connori Raised in Captivity.

Schizothorax o'connori (S. o'connori) is a representative tetraploid species in the subfamily Schizothoracinae and an important endemic fish in the Qinghai-Tibet Plateau. However, the domestication of S. o'connori remains challenging due to the lack of basic research. Here, we investigated the effects of artificial feeding on the oocytes and liver of S. o'connori by comparing the histological, metabolomic, and transcriptomic data. Histological results showed that the oocytes and liver of captive-reared S. o'connori had abnormal cell morphology. After comparison with the self-built database, a total of 233 metabolites were annotated. In oocytes, a total of 37 differentially accumulated metabolites (DAMs) were detected and two pathways were significantly enriched. There were obvious differences in the metabolites related to ovarian development, including pregnenolone and arachidonic acid. In liver, a total of 70 DAMs were detected and five pathways were significantly enriched. Based on the transcriptomic data, a total of 159 differentially expressed genes (DEGs) were significantly related with cell growth and death pathway in oocytes, while a total of 2841 DEGs were significantly related with 102 pathways in liver. Comparing the metabolomic and transcriptomic data showed that there were three common significant enrichment pathways in liver, including biosynthesis of unsaturated fatty acids, starch and sucrose metabolism, and fatty acid biosynthesis. These results showed that special attention should be given to the composition and intake of fatty acids during the artificial breeding of S. o'connori. In addition, many of metabolite-gene pairs were related to adenosine 5'-diphosphate, adenosine monophosphate, and pregnenolone. In summary, these data provide an overview of global metabolic and transcriptomic resources and broaden our understanding of captive-reared S. o'connori.

[Distribution of melanin in the larvae of Schizothorax o'connori]. / å¼‚é½¿è£‚è ¹é±¼ä»”é±¼çš„é»‘è‰²ç´ åˆ†å¸ƒ.

We examined the distribution of melanin during the development of the larvae of Schizothorax o'connori except the eyes with histological method. The results showed that after hatching, the appearance sequence of melanin in different organs were following an order of the outer membrane of neurocranium, the pericardial cavity and the dorsal skin, and the peritoneum and the spinal cord. Specifically, melanin appeared in the outer membrane of neurocranium around 5 DAH (days after hatching), in the pericardial cavity and the back skin at 7 DAH, and in the peritoneum and the spinal cord at 10 DAH. Melanin was found in the skin and internal organs (the outer membrane of neurocranium, the pericardial cavity, the peritoneum, the spinal cord) of S. o'connori at 10 DAH, which was mainly distributed on the back. The appearance and distribution of melanin in the postembryonic development of S. o'connori might be related to the high ultraviolet radiation. Our results could provide reference for further research on the UV protection mechanism of melanin for fish and provide theoretical support for the optimization of rearing conditions for larvae in the plateau.

Genome of Tetraploid Fish Schizothorax o'connori Provides Insights into Early Re-diploidization and High-Altitude Adaptation.

Whole-genome duplications (WGDs) of Schizothoracinae are believed to have played a significant role in speciation and environmental adaptation on the Qinghai-Tibet Plateau (QTP). Here, we present a genome for Schizothorax o'connori, a QTP endemic fish and showed the species as a young tetraploid with a recent WGD later than ∼1.23 mya. We exhibited that massive insertions between duplicated genomes caused by transposon bursts could induce mutagenesis in adjacent sequences and alter the expression of neighboring genes, representing an early re-diploidization process in a polyploid genome after WGD. Meanwhile, we found that many genes involved in DNA repair and folate transport/metabolism experienced natural selection and might contribute to the environmental adaptation of this species. Therefore, the S. o'connori genome could serve as a young tetraploid model for investigations of early re-diploidization in polyploid genomes and offers an invaluable genetic resource for environmental adaptation studies of the endemic fish of the QTP.

Full-length transcript sequencing accelerates the transcriptome research of Gymnocypris namensis, an iconic fish of the Tibetan Plateau.

Gymnocypris namensis, the only commercial fish in Namtso Lake of Tibet in China, is rated as nearly threatened species in the Red List of China's Vertebrates. As one of the highest-altitude schizothorax fish in China, G. namensis has strong adaptability to the plateau harsh environment. Although being an indigenous economic fish with high value in research, the biological characterization, genetic diversity, and plateau adaptability of G. namensis are still unclear. Here, we used Pacific Biosciences single molecular real time long read sequencing technology to generate full-length transcripts of G. namensis. Sequences clustering analysis and error correction with Illumina-produced short reads to obtain 319,044 polished isoforms. After removing redundant reads, 125,396 non-redundant isoforms were obtained. Among all transcripts, 103,286 were annotated to public databases. Natural selection has acted on 42 genes for G. namensis, which were enriched on the functions of mismatch repair and Glutathione metabolism. Total 89,736 open reading frames, 95,947 microsatellites, and 21,360 long non-coding RNAs were identified across all transcripts. This is the first study of transcriptome in G. namensis by using PacBio Iso-seq. The acquisition of full-length transcript isoforms might accelerate the transcriptome research of G. namensis and provide basis for further research.

Three forms of cocaine- and amphetamine-regulated transcript may be involved in food intake regulation in gibel carp (Carassius auratus gibelio).

In fish, as in mammals, several studies have demonstrated that the cocaine- and amphetamine-regulated transcript (CART) plays an important role in feeding. However, thus far, the function of CART in gibel carp (Carassius auratus gibelio) feeding regulation has not been reported. In our study, we first identified three forms of CART peptide precursors from gibel carp brain and named these CART-1, CART-2, and CART-3. The full-length cDNA sequences of CART-1, CART-2, and CART-3 were 616 bp, 705 bp, and 760 bp, respectively, encoding peptides of 118, 120, and 104 amino acid residues. We detected mRNA expression of CART-1, CART-2, and CART-3 in a wide range of peripheral and central tissues, with the highest expression detected in the brain. After a meal, mRNA expression of CART-1, CART-2, and CART-3 was significantly elevated, suggesting that CART-1, CART-2, and CART-3 may act as postprandial satiety signals. Moreover, mRNA expression of all three CART-1, CART-2, and CART-3 was significantly reduced during fasting and significantly elevated with refeeding. Our findings indicate that CART-1, CART-2, and CART-3 might function as a satiety factor in the gibel carp.

Structural and functional characterization of peptide YY on feeding in Schizothorax davidi.

Several studies have demonstrated that the neuropeptide peptide YY (PYY) plays an important role in feeding in mammals and fish. However, thus far, the feeding regulation function of PYY in Schizothorax davidi has not been well understood. Here, we identified the full-length cDNA sequence of PYY in S. davidi for the first time. S. davidi PYY contains 803 bp nucleotides including a 328 bp 3' untranslated region (UTR), a 181 bp 5' UTR, and a 294 bp open reading frame encoding a peptide of 97 amino acids. S. davidi PYY expression was observed in almost all tissues, with the highest expression detected in the hypothalamus. PYY mRNA expression in the hypothalamus was significantly elevated after a meal (P < 0.01), and significantly decreased after fasting (P < 0.01). PYY expression levels were increased sharply following refeeding after 9 days (P < 0.01), suggesting that it might function as a satiety factor in S. davidi.

The complete mitochondrial genome of the Gymnocypris chui (Cypriniformes: Cyprinidae).

The Gymnocypris chui, a new recorded species in Lange Lake, was grouped into genus Gymnocypris in Schizothoracinae, and had the rare quantity and limited resources on biology and genetics, especially in the mitochondrion. In this study, the complete mitochondrial sequence of G. chui was assembled and phylogenetic relationships with other species in Cyprinidae were analyzed. The whole mitochondrial sequence was 16,864 bp in length, which contained two control regions (D-loop regions), two rRNA genes (12S and 16S rRNA), 13 protein-coding genes and 22 tRNA genes. The D-loop region was separated by tRNAPro . The 12S rRNA and 16S rRNA located between tRNAPhe and tRNALeu and were separated by tRNAVal . The 13 mRNAs had three start codons, five termination codons and four overlap regions. The 22 tRNA scattered among the whole mitochondrion, and they were range from 66 (tRNACys ) to 76 (tRNALys andtRNALeu ) in length. To further explore the phylogenetic relationship of the G. chui, we constructed the phylogenetic tree and verified that the G. chui was a part of genus Gymnocypris and had closer relationship with Gymnocypris dobula and was independent from other species of Schizothoracinae, Barbinae and Labeoninae in Cyprinidae. This study provided the valuable evidence on phylogenetic relationship of the G. chui at the molecular level and essential resource for further research on this species.

Complete mitochondrial genome and phylogenetic analysis of Schizothorax molesworthi (Cypriniformes: Cyprinidae).

Schizothorax molesworthi is an endemic species and distributes in the MoTuo reaches of the Yarlung Zangbo River. It is one of the most important commercial fishes in this area. In the present study, the complete mitochondrial DNA sequence of Schizothorax molesworthi was determined and analyzed. The mitochondrial genome of Schizothorax molesworthi is 16,585 bp in length and consisted of 37genes in the typical vertebrate mitochondrial gene arrangement. Overall base composition of mitochondrial genome of Schizothorax molesworthi was 30.1% A, 26.9% C, 17. 4% G, and 25.6% T, with a high A + T content (55.7%). Phylogenetic analysis showed that Schizothorax molesworthi and Schizothorax plagiostomus clustered together in a clade and formed a sister relationship.

Evidence that ghrelin may be associated with the food intake of gibel carp (Carassius auratus gibelio).

Ghrelin, a non-amidated peptide hormone, is a potent anorectic neuropeptide implicated in feeding regulation in mammals and non-mammalian vertebrates. However, the involvement of ghrelin in the feeding behavior of teleosts has not been well understood. To better understand the role of ghrelin in the regulation of appetite in fish, in this study, we cloned the cDNAs encoding ghrelin and investigated their mRNA distributions in gibel carp tissues. We also assessed the effects of different nutritional status on ghrelin mRNA abundance. Ghrelin mRNAs were ubiquitously expressed in ten tissues (intestine, liver, brain, mesonephron, head kidney, spleen, skin, heart, muscle, gill and pituitary gland), and relatively high expression levels were detected in the gut. Postprandial studies analysis revealed a significant postprandial decrease in ghrelin mRNA expression in the gut (1 and 3 h after the regular feeding time). In addition, ghrelin mRNA expression in the gut significantly increased at day 7 after fasting and declined sharply after refeeding, which suggested that ghrelin might be involved in the regulation of appetite in gibel carp. Overall, our result provides basis for further investigation into the regulation of feeding in gibel carp.