Genome-wide identification and expression profiling of HSD3B and SDR42E1 genes in the Pacific oyster (Crassostrea gigas): potential associations with gonadal development.
This study identifies candidate genes associated with gonadal development in Pacific oysters, but does not demonstrate their regulatory roles.
Where it sits
this study against the rest of the dsip corpusSummary and findings
This study identified and profiled the expression of five genes related to HSD3B and SDR42E1 in the Pacific oyster (Crassostrea gigas). The research focused on their potential associations with gonadal development. No treatment effects or therapeutic claims were reported.
Abstract
Sex steroids are lipid-soluble signaling molecules that regulate sex differentiation, reproductive development and physiological homeostasis in animals. 3β-Hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase (3β-HSD) is a key steroidogenic enzyme, whereas SDR42E1, an extended short-chain dehydrogenase/reductase, has been implicated in sterol- and steroid-related metabolism. However, the composition, evolutionary relationships and expression patterns of the HSD3B- and SDR42E1-related genes in bivalve gonadal development remain poorly characterized. In this study, five PF01073-containing genes, comprising three CgHsd3b and two CgSdr42e1 genes, were identified in the Pacific oyster Crassostrea gigas. Phylogenetic analysis separated the proteins into HSD3B-related and SDR42E1-related groups, and gene-structure and motif analyses indicated subfamily-level divergence. All five proteins retained the SDR domain but differed in exon-intron structure and motif composition. Each contained the extended-SDR TGxxGxxG motif, whereas exact classical [ST]GxxxGxG and NNAG motifs were absent. Tyr- and Lys-equivalent residues were conserved, while the HSD3B1 Ser-equivalent position contained Thr in two C. gigas proteins and Ser in one. These features support their classification as extended-SDR proteins but do not establish enzymatic activity or substrate specificity. The three CgHsd3b genes were dispersed on one chromosome, whereas CgSdr42e1-1 and CgSdr42e1-2 were adjacent on another chromosome, suggesting a possible local duplication event for the CgSdr42e1 pair. Public RNA-seq data showed distinct tissue- and gonadal-stage expression patterns, with several genes displaying gonad-biased or female-stage-associated expression. Independent RT-qPCR profiling of the representative genes CgHsd3b-3 and CgSdr42e1-1 detected stage-dependent expression, although tissue rankings differed from those in the public RNA-seq datasets. These differences may reflect the use of independent biological samples, tissue composition, normalization procedures, and platform-specific measurements. Because enzymatic assays, metabolite measurements, cellular localization, and functional perturbation were not performed, the results identify candidate genes whose expression is associated with gonadal development rather than demonstrating regulatory roles. This study provides a comparative framework for future functional investigation of sterol- and steroid-related metabolism in bivalves.
Background
The paper addresses the roles of sex steroids in regulating reproductive development and physiological homeostasis in animals. Previous studies have identified key enzymes involved in steroid metabolism, but the specific genes related to HSD3B and SDR42E1 in bivalves have not been well characterized. Understanding these genes is crucial for elucidating their roles in gonadal development.
Methods
The study involved genome-wide identification and expression profiling of genes in the Pacific oyster. It included phylogenetic analysis, gene-structure, and motif analyses. Public RNA-seq data and independent RT-qPCR were utilized to assess gene expression across different tissues and gonadal stages.
Results
The study identified five genes related to HSD3B and SDR42E1. RNA-seq data revealed distinct expression patterns, with some genes showing gonad-biased or female-stage-associated expression. RT-qPCR confirmed stage-dependent expression for specific genes.
Interpretation
The findings contribute to the understanding of gene expression related to gonadal development in bivalves. However, the study does not establish any functional roles for the identified genes due to the lack of enzymatic assays. The results suggest potential avenues for future research but do not provide clinically meaningful insights.
Key findings
- Five PF01073-containing genes identified: three CgHsd3b and two CgSdr42e1.
- Distinct tissue- and gonadal-stage expression patterns observed in public RNA-seq data.
- Stage-dependent expression detected for CgHsd3b-3 and CgSdr42e1-1 via RT-qPCR.
Limitations
- No enzymatic assays performed.
- No metabolite measurements conducted.
- Expression patterns may vary due to different biological samples.
- Short follow-up on functional implications.