الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
A study conducted at Huazhong Agriculture University in Wuhan, China, aimed to enhance the production of the Blunt Snout Bream (BSB) by conducting distant hybridization between Megalobrama amblycephala and Eliopichthys bambusa. The goal was to produce hybrid with high hybrid vigor, combining desired traits from both parents. The hybridization showed lower fertilization and hatching rates than the pure breed, with 64% and 59% respectively. The hybrid also showed growth vigor, with notable differences in SGR, FCR, and AWG. A challenge experiment with Aeromonas hydrophila was conducted, and the hybrid fish exhibited no internal or exterior clinical signs. The study used next-generation sequencing technology to comprehensively analyze the transcriptome profiles of response-related genes in the hybrid compared to the BSB. Data facilitating further research into the resistance and susceptibility of the fish species to exogenously invasive pathogens. The data analysis also revealed significant differences in immune-related gene expression, the main results were as follows:
1- The study aimed to determine the pathogenicity of A. hydrophila in hybrid compared BSB and to understand the immune response to A. hydrophila infection.
2- RNA-Seq technology was used to analyze the transcriptomic profile after artificial bacterial infection. cDNA libraries from tissues were collected from challenged hybrid and challenged pure breed BSB, injected with A. hydrophila. 91164 unigenes were isolated and annotated using BLASTX. The annotated unigenes were classified into three GO categories: biological processes, cellular components, and molecular functions. The unigenes were assigned to 25 KOG categories, with the most common being signal transduction mechanism. The three predominant pathways were signal transduction, immune system, and global and overview maps. Interestingly, several pathways associated with immune-related systems and disease processes were identified in the database. In total, 235 significantly differentially expressed unigenes were immune-related genes and distributed in 13 signaling pathways.
3- The hybrid transcriptome profiles identified 23409 microsatellites, with dinucleotide repeats being the most common. The lengths of these repeats ranged from 12 to 25 bp.
4- The genes in the hybrid were differentially expressed in response to A. hydrophila infection compared to infected pure breed BSB. The RPKM technique was used to determine the differential expression of transcripts between the two transcriptomes. The FPKM distribution was 520,085 (52.7%) in the hybrid group and 466,369 (47.3%) in the BSB group. The genes with the most significant differential expression were 36075, 34271, and 25783, respectively.
5- The study utilized reverse transcription-quantitative PCR (RT-qPCR) to analyze the response of selected genes (H2-Eb1, PIGR, HLA-DRA, IRF1, IRF8, NFKB, CASP1, CD209, MALToma, IL1B, IL-6, baculoviral IAP, UBE2D2, GSK-3 beta and GTPase Krasin) to A. hydrophila. The results showed that these genes were highly up or downregulated in the intestine, kidney, and liver during the challenge time 12 hours post-infection, indicating differential expression levels in the transcriptome.
The study compared the morphological characteristics of Megalobrama amblycephala, Elopichthys bambusa, and their hybrid offspring. The hybrid offspring had traits consistent with the female parent Megalobrama amblycephala and male parent Elopichthys bambusa, but more traits were closer to the female parent.
The mitochondrial genome of the hybrid fish was identified, with a full-length sequence of 16623 BP, consistent with the female parent. The mitochondrial genome encodes 37 genes, including 13 protein coding genes, 22 trna genes, and 2 rrna genes. The phylogenetic tree showed a close genetic relationship between the Megalobrama amblycephala (♀) × Elopichthys bambusa (♂) cross breed and the female parent Megalobrama amblycephala, but far from the male parent Elopichthys bambusa.
This research highlights the important roles of these genes in the hybrid compared to pure breed BSB’s innate immune system. The results provide valuable molecular data for further study of immunogenetics of BSB, breeding programs, and selective breeding.