The aim of this study was to investigate the energy sources and utilization patterns during embryonic development of Chinese sturgeon through analyzing the biochemical components of embryos at different development stages, and to explore the physiological characteristics and related molecular mechanism during embryogenesis in combination with an embryonic transcriptome analysis. Chinese sturgeon embryo samples were collected at different development stages (fertilized eggs, neurula stage, and tail touching head stage). The results showed that embryonic development was a process of continuous energy consumption. The change of total protein content was consistent with total amino acid content, showing a trend of increasing first and then decreasing. However, the total lipid content decreased significantly during early embryonic development. As for amino acid profile, leucine, arginine and lysine contents showed the highest level within essential amino acids (EAA), while glutamic acid, alanine, aspartic acid and serine contents showed the highest level within non-essential amino acids (NEAA). In terms of fatty acid content, the main quantitative fatty acids were C16:0 in saturated fatty acids (SFA), C18:1 in monounsaturated fatty acids (MUFA), and C22:6n-3 (DHA), C18:2n-6 as well as C20:5n-3 (EPA) in polyunsaturated fatty acids (PUFA). The content of C20:4n-6 (ARA), EPA and DHA were increased at neurula stage compared to fertilized eggs, which indicated their important roles in the structural composition during embryogenesis. Notably, Chinese sturgeon may have the ability to elongate n-3 PUFA to partially meet its requirements for highly unsaturated fatty acids (HUFA) during embryonic development. Transcriptome analysis showed that 19,078 and 6326 differential expressed genes (DEGs) were up-regulated and down-regulated respectively from fertilized eggs to neurula stage; while 3556 and 3150 DEGs were up-regulated and down-regulated respectively from neurula stage to tail touching head stage. KEGG enrichment analysis showed that the protein processing pathway was significantly enriched in early embryonic development through the up-regulated genes of imp4, pwp2, utp21, nop10, rpl10_17_35 and rps25; while the down-regulated genes of ccne1, ccna2, ccnb1, cdk1_2 and plk1 were associated with cell proliferation and differentiation pathway. In late embryonic development, the pathways related to aerobic metabolism, amino acid metabolism and lipid metabolism were significantly enriched through the up-regulated genes of mdh1, fumc, idh2, elovl6 and dgat2; and the neuroactive ligand-receptor interaction pathway was significantly down-regulated. In general, this study revealed the continuous energy consumption during embryonic development of Chinese sturgeon with specific energy substrates at different stages, and highlighted the DEGs and related pathway involved in the ontogeny and nutrient metabolism, which emphasizes the essentiality of high quality egg production for the success of captive breeding of Chinese sturgeon and would guide the broodstock nutrition for high quality egg production.
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