Chromosome-scale assembly and high-density genetic map of the yellow drum, Nibea albiflora

Reproduction in yellow drum (Nibea albiflora): insights from endocrine regulation and intestinal microbiota changes during reproductive season

The yellow drum (Nibea albiflora), a pivotal species within the Sciaenidae family, is economically important in the mariculture along the coastal regions of China. A comprehensive understanding gonadal maturation and spawning processes is crucial for seed production in the artificial propagation of yellow drum. This study investigates serum hormonal fluctuations, gonadal histological features, sex hormone receptor gene expression, and intestinal microbiota composition in both male and female yellow drum during the reproductive season. Twenty individuals were sampled from reproductive stages IV, V, and VI, respectively. During the spawning season, no significant differences were observed in the levels of PROG, E2, and 11-KT across different stages, in both males and females, with no significant sex-based differences. Subsequent analysis indicated a significant upregulation of fshr, lhcgr, and esr expression in the ovary during spawning stages. In contrast, within the testis, the expression levels of fshr, ar, and esr remained relatively constant across different stages, whereas lhcgr expression was markedly higher during the spawning stages compared with prespawning and post-spawning stages. Analysis of intestinal microbiota revealed a predominance of Bacteroidota, Firmicutes, and Proteobacteria, with no significant sex differences. At the class level, the abundances of Alphaproteobacteria, Gammaproteobacteria, and Bacilli exhibited significant fluctuations during the spawning and post-spawning stages in both sexes. At the genus level, g_Muribaculaceae and g_Bacteroides were abundant during spawning stages in both sexes. A Mantel test showed significant positive correlations between PROG levels and the abundances of g_Bacteroides in males. In females, PROG levels were positively correlated with the abundance of g_Prevotella. These findings enhance our understanding of the interplay between reproductive biology and the biological functions of intestinal microbiota in yellow drum broodstock during the reproductive season, thereby laying a foundation for the development of artificial propagation technology in this species.

Characterization and functional analysis of interleukin-6 and its receptor subunits (IL-6Rα and IL-6Rβ) in the yellow drum, Nibea alibiflora

Interleukin 6 (IL-6) is one of the cytokines found to be multifunctional and biologically effective, regulating immune and inflammatory response by interacting with receptors to transmit signals. In this study, the full-length cDNAs of IL-6 (named as NaIL-6) and its receptors IL-6R and gp130 (named as NaIL-6Rα and NaIL-6Rβ) of Nibea albiflora were acquired and they possessed the typical symbolic motifs similar to its teleost orthologues in multiple sequence comparisons. The phylogenetic trees showed that NaIL-6 and its receptors clustered with their counterparts in bony fish, and had the closest affinity to Larimichthys crocea. Real-time PCR indicated that NaIL-6, NaIL-6Rα and NaIL-6Rβ were widely expressed in different tissues, among which NaIL-6 was highly expressed in the liver, NaIL-6Rα showed the highest expression in the kidney and NaIL-6Rβ was reflected in the liver. Following stimulation by Vibrio parahaemolyticus, Vibrio alginolyticus, or Polyinosinic-polycytidylic acid (Poly (I:C)) infection, the mRNA expression of all three genes were greatly up-regulated over time. The cell localization analysis showed that NaIL-6 distributed in cytoplasm and cell membrane, and NaIL-6Rα located on the cell membrane. After co-transfection of NaIL-6- mCherry and NaIL-6Rα-EGFP, they co-expressed as orange at the same position for their possibility of spatial interactions on the cellular membrane. By GST-Pull down with the purified target proteins, the association between NaIL-6-His and NaIL-6Rα-GST was confirmed, which may be utilized for further functional study. Taken together, the results indicated that the biological functions of NaIL-6 and its receptors NaIL-6Rα and NaIL-6Rβ involved in the immunologic mechanism in N.albiflora, which would provide a basis for the research of immune functions and signaling pathway of IL-6 and its receptors in fish.

A C-type lectin-like receptor CD302 in yellow drum (Nibea albiflora) functioning in antibacterial activity and innate immune signaling

Molecular dissection of disease resistance against Vibrio harveyi infection in yellow drum at the genome-wide level uncovered a C-type lectin-like receptor cluster of differentiation CD302 (named as YdCD302) in our previous study. Here, the gene expression pattern of YdCD302 and its function in mediating the defense response to V. harveyi attack were investigated. Gene expression analysis demonstrated that YdCD302 was ubiquitously distributed in various tissues with the highest transcript abundance in liver. The YdCD302 protein exhibited agglutination and antibacterial activity against V. harveyi cells. Binding assay indicated that YdCD302 can physically interact with V. harveyi cells in a Ca2+-independent manner, and the interaction can activate reactive oxygen species (ROS) production in the bacterial cells to induce RecA/LexA-mediated cell death. After infection with V. harveyi, the expression of YdCD302 can be up-regulated significantly in the main immune organs of yellow drum and potentially further trigger the cytokines involved innate immunity. These findings provide insight into the genetic basis of the disease resistance trait in yellow drum and shed light on the functioning of the CD302 C-type lectin-like receptor in host-pathogen interactions. The molecular and functional characterization of YdCD302 is a significant step towards a better understanding of disease resistance mechanisms and the development of new strategies for disease control.

Comparative Transcriptome Analyses Characterize Expression Signatures Among Males, Females, Neo-Males, and Gynogenetic Females in the Yellow Drum (Nibea albiflora)

The yellow drum (Nibea albiflora) is one of the most important marine economic fish in China, and its sexually dimorphic growth makes it preferable for mono-sex culture. Although gynogenesis and neo-male induction techniques have been established, the molecular pathways and regulatory mechanisms of sex determination and maintenance in gynogenetic females and neo-males remains far from fully understood. In this study, the gene expression profiles were investigated in the gonads and brains of wild-type male, wild-type female, neo-male, and gynogenetic female yellow drum using comparative transcriptome analyses. Generally, a total of 52,999 novel transcripts were obtained in RNA-seq, of which 45,651 were isoforms of known protein-coding genes, 1,358 novel protein-coding genes, and 5,990 long non-coding RNAs. We found that the differences between wild-type males and neo-males and between wild-type females and gynogenetic females were relatively small at both the histological and transcriptomic levels, indicating that artificial gynogenesis or hormonal sex reversal may have minimal effects on normal female or male life function, respectively. In the brain, pathways such as “Oocyte meiosis”, “Cell cycle”, and “Riboflavin metabolism” were found to be significantly enriched. In the gonads, pathways such as “Prolactin signaling pathway”, “PPAR signaling pathway”, “Cholesterol metabolism”, and “Jak-STAT signaling pathway” were found to play important roles in maintaining the regular proliferation and differentiation of females and males in yellow drum. In particular, we found that zp4 might be an effective molecular marker to differentiate between gynogenetic and normal females owing to its unique expression pattern. The results of this study may help to elucidate the molecular mechanisms involved in sex maintenance in the gonads and brain and provide basic data for genetic breeding of the yellow drum.