Chao Zhao

Background: Primordial germ cells (PGC) are the progenitor cells of sperm and eggs during the embryonic stage. The maternal gene vasa has been widely studied for its role in PGC origin, and other genes like dead end (dnd) have also been identified. Objectives: Spotted sea bass is an important economic marine fish, and the study of its germ cell characteristics provides important basic data for future population breeding and protection. Methods: In this study, we cloned the full-length sequences of Lmvasa (2384 bp, encoding 1905 aa) and Lmdnd (1523 bp, encoding 386 aa) using RACE. Temporal and spatial expression patterns of Lmvasa and Lmdnd in embryos and gonads were analyzed by PCR, immunohistochemistry, and in situ hybridization. We also used microinjections of chimeric RNA containing GFP and Lmvasa 3′ UTR to visualize PGCs. Results: Our results showed that Lmvasa and Lmdnd are expressed primarily in early embryonic development (pre-blastula stage) and were expressed only in the gonads. Immunohistochemistry revealed abundant expression of Lmvasa and Lmdnd proteins in spermatogonia, weak expression in spermatocytes, and no expression in spermatozoa. In ovaries, both genes were expressed throughout oogenesis. Furthermore, PGCs in spotted sea bass belonged to an early localization pattern. Microinjection experiments demonstrated that Lmvasa 3′ UTR effectively labeled PGCs in embryos of spotted sea bass, zebrafish, and medaka. Conclusions: These findings may contribute to understanding PGC development in spotted sea bass and other Percidae.

Fish reproduction requires suitable salinity and temperature, as well as sufficient energy. This study investigated temperature and salinity effects on ovarian development of Lateolabrax maculatus and energy metabolism differences between reproduction and growth. Two salinities (4‰ and 30‰) and temperatures (18 ± 1 °C and 30 ± 1 °C) formed four treatments: SWNT (30‰, 30 ± 1 °C), SWLT (30‰, 18 ± 1 °C), FWLT (4‰, 18 ± 1 °C), and FWNT (4‰, 30 ± 1 °C). GSI and sex hormones (FSH, LH, E2, and 17α,20β-DHP) were measured. Transcriptome analysis explored how temperature and salinity regulate ovarian development in L. maculatus, while integrated transcriptomic and targeted energy metabolomic analyses revealed energy metabolism differences between ovary and muscle during this process. The results showed that low salinity (4‰) and low temperature (18 ± 1 °C) synergistically promoted ovarian development in the FWLT group, as indicated by a significant increase in GSI and elevated levels of key sex hormones (FSH, LH, E2, and 17α,20β-DHP). Transcriptome analysis showed that low temperature activated pathways involved in steroidogenesis, oocyte maturation, and meiosis, and genes such as ADCY6, PRKACB, CPEB4, FZD7-A, and CCND2 were significantly upregulated. Salinity changes mainly affected amino acid metabolism, cholesterol metabolism, and the insulin signaling pathway. Genes such as PCSK9 and CKM may regulate ovarian development by regulating hormone synthesis and energy metabolism. Comprehensive transcriptome and metabolome analyses show that glycolysis is downregulated and oxidative phosphorylation is upregulated in the ovary, suggesting that ovarian oogenesis tends to be energized by aerobic metabolism. The TCA cycle may be used more for providing biosynthetic precursors and facilitating the transport of substrates between the mitochondrion and the cytoplasm rather than just as a source of ATP. Muscle tissue relies primarily on glycolysis for rapid energy production and may redistribute energy to the gonads, prioritizing the energy needs of the ovaries and contributing to the dynamic balance between reproduction and growth. This study provides insights into the molecular mechanisms of how environmental factors regulate fish reproduction, providing a theoretical basis and potential molecular targets for the regulation of reproduction and optimization of aquaculture environments.

Growing evidence suggests a close relationship between gut microbiota and infectious diseases. However, the specific role of gut microbiota in host-pathogen interactions during aquaculture-related infections remains poorly understood. This study investigated the diversity and composition of gut microbiota communities in Aeromonas veronii -infected Lateolabrax maculatus using high-throughput sequencing. The results revealed significant changes in the structure and composition of L. maculatus gut microbiota after A. veronii infection. Over time, Bacteroidetes and Firmicutes decreased significantly, while Proteobacteria increased significantly after A. veronii infection. Most intestinal bacteria showed a decline in abundance over time, with probiotics (such as Lactobacillus ) experiencing a significant decrease and pathogens (such as Aeromonas ) showing a significant increase. Conversely, no differences were observed in the structure and composition of gut microbiota between healthy L. maculatus and those infected with A. veronii after treatment with Lactobacillus plantarum ; no changes in relative abundances of other bacterial phyla or genera except for Aeromonas . Furthermore, intestinal flora’s structural diversity and composition differed significantly from untreated L. maculatus infected with A. veronii . These findings suggest alterations in the structure and composition of gut microbiota following A. veronii infection. L. plantarum can maintain a dynamic balance within the intestinal flora, reducing the potential risk of pathogen infections.

The present study was conducted to investigate the effects of high dietary carbohydrate levels on growth performance, enzyme activities, and gene expressions related to liver glucose metabolism and the intestinal microbiota of Lateolabrax maculatus juveniles. Two experimental diets with levels of carbohydrates (20% and 30%, named the NCD group and the HCD group, respectively) were designed to feed L. maculatus (initial weight 9.45 ± 0.03 g) for 56 days. The results showed that, compared with the NCD group, the condition factor (CF) was significantly elevated in the HCD group (p < 0.05). The plasma advanced glycosylation end products (AGEs), glycated serum protein (GSP), total cholesterol (TC), triglycerides (TG), high-density lipoprotein (HDL), low-density lipoprotein (LDL), and glutamate aminotransferase (AST) were significantly higher in the HCD group than those in the NCD group (p < 0.05). The intestinal lipase, chymotrypsin, and α-amylase in the HCD group were significantly higher than those in the NCD group (p < 0.05). The liver superoxide dismutase (SOD), total antioxidant capacity (T-AOC), and catalase (CAT) were significantly lower in the HCD group than in the NCD group (p < 0.05). The liver malondialdehyde (MDA) and hexokinase (HK) levels were significantly higher than those in the NCD group (p < 0.05). In the histopathological findings, liver cells in the HCD group appeared to have many vacuoles, and the number of lipid droplets increased. Compared with the NCD group, the relative expression of liver glucokinase (GK) and glycogen synthetase kinase-3 (GSK3β) genes in the HCD group was significantly increased (p < 0.05), while the relative expression of phosphoenolpyruvate carboxykinase (PEPCK) and glycogen phosphorylase (GP) genes in the HCD group was significantly reduced (p < 0.05). High-throughput 16S rRNA gene sequencing showed that high dietary carbohydrate intake changed the composition and structure of the intestinal microbiota. At the phylum level of the intestinal microbiota, high dietary carbohydrates decreased the relative abundance of Firmicutes and increased the relative abundance of Proteobacteria and Bacteroidetes. At the genus level of the intestinal microbiota, high carbohydrates decreased the relative abundance of Bacillus and increased the relative abundance of Photobacterium and Paraclostridium. From the results of this experiment on L. maculatus, high carbohydrates led to increased condition factor and liver glycogen, lipid deposition, decreased antioxidant capacity of the liver, increased relative abundance of harmful intestinal microorganisms, and disrupted glucose metabolism.

The insulin-like growth factor 2 gene (igf2) is thought to be a key factor that could regulate animal growth. In fish, few researchers have reported on the single nucleotide polymorphisms (SNPs) located in igf2 and their association with growth traits. We screened the SNPs of igf2 from the spotted sea bass (Lateolabrax maculatus) by Sanger sequencing and made an association between these SNPs with growth traits. The full-length complementary (c) DNA of igf2 was 1045 bp, including an open reading frame of 648 bp. The amino acid sequence of Igf2 contained a signal peptide, an IGF domain, and an IGF2_C domain. Multiple sequence alignment showed that the IGF domain and IGF2_C domain were conserved in vertebrates. The genome sequence of igf2 had a length of 6227 bp. Fourteen SNPs (13 in the introns and one in one of the exons) were found in the genome sequence of igf2. Four SNPs located in the intron were significantly associated with growth traits (p < 0.05). These results demonstrated that these SNPs could be candidate molecular markers for breeding programs in L. maculatus.