Comparative transcriptome analysis of three gonadal development stages reveals potential genes involved in gametogenesis of the fluted giant clam (Tridacna squamosa)

Abstract

Background Gonad development and differentiation is an essential function for all sexually reproducing species, and many aspects of these developmental processes are highly conserved among the metazoa. However, the mechanisms underlying gonad development and gametogenesis remain unclear in Tridacna squamosa, a large-size bivalve of great ecological value. They are protandrous simultaneous hermaphrodites, with the male gonad maturing first, eventually followed by the female gonads. In this study, nine gonad libraries representing resting, male and hermaphrodite stages in T. squamosa were performed to identify the molecular mechanisms. Results Sixteen thousand four hundred ninety-one unigenes were annotated in the NCBI non-redundant protein database. Among the annotated unigenes, 5091 and 7328 unigenes were assigned to Gene Ontology categories and the Kyoto Encyclopedia of Genes and Genomes (KEGG) Pathway database, respectively. A total of 4763 differentially expressed genes (DEGs) were identified by comparing male to resting gonads, consisting of 3499 which were comparatively upregulated in males and 1264 which were downregulated in males. Six hundred-ninteen DEGs between male and hermaphroditic gonads were identified, with 518 DEGs more strongly expressed in hermaphrodites and 101 more strongly expressed in males. GO (Gene Ontology) and KEGG pathway analyses revealed that various biological functions and processes, including functions related to the endocrine system, oocyte meiosis, carbon metabolism, and the cell cycle, were involved in regulating gonadal development and gametogenesis in T. squamosa. Testis-specific serine/threonine kinases 1 (TSSK1), TSSK4, TSSK5, Doublesex- and mab-3-related transcription factor 1 (DMRT1), SOX, Sperm surface protein 17 (SP17) and other genes were involved in male gonadal development in Tridacna squamosal. Both spermatogenesis- (TSSK4, spermatogenesis-associated protein 17, spermatogenesis-associated protein 8, sperm motility kinase X, SP17) and oogenesis-related genes (zona pellucida protein, Forkhead Box L2, Vitellogenin, Vitellogenin receptor, 5-hydroxytryptamine, 5-hydroxytryptamine receptor) were simultaneously highly expressed in the hermaphroditic gonad to maintain the hermaphroditism of T. squamosa. Conclusion All these results from our study will facilitate better understanding of the molecular mechanisms underlying giant clam gonad development and gametogenesis, which can provided a base on obtaining excellent gametes during the seed production process for giant clams.

Expression of the Testis-Specific Serine/Threonine Kinases Suggests Their Role in Spermiogenesis of Bay Scallop Argopecten irradians

“…But just like other Tssk members, Tssk5 have the conserved lysine residue ( Figure 2 ) that is involved in ATP binding. Moreover, Tssk5 has the same expression pattern in male testis as other Tssk members in the bay scallop A. irradians (this study), Yesso scallop P. yessoensis , and clam Tridacna squamosa ( Li et al, 2020 ). Considering the presence of key amino acids and the similar expression pattern with other Tssk members, we assume that Tssk5 may be a functional gene in mollusks.…”

“…For a precise reproductive control during the breeding process, a comprehensive understanding of molecular mechanism underlying gametogenesis is required. Massive screening of reproduction-specific genes in scallop Argopecten purpuratus ( Boutet et al, 2008 ), mussel Mytilus edulis ( Ciocan et al, 2011 ), and clam Tridacna squamosa ( Li et al, 2020 ) revealed that Tssk genes are involved in sexual maturation of testis. However, only Tssk1 has been cloned and characterized in mollusks.…”

Sexual Development of the Hermaphroditic Scallop Argopecten irradians Revealed by Morphological, Endocrine and Molecular Analysis

“…In the sequential hermaphrodites, a potential sex-determining pathway containing SoxH, Dmrt, and FoxL2 has been proposed in the Pacific oyster Crassostrea gigas ( Zhang et al, 2014 ), and Fem1-like, Dmrt, and FoxL2 are considered as key sex-determining genes in the pearl oyster Pinctada margaritifera ( Teaniniuraitemoana et al, 2014 , 2015 ). Recent studies reported the transcriptome sequencing of two simultaneous hermaphroditic bivalves, lion-paw scallop Nodipecten subnodosus and giant clam Tridacna squamosa , from which several sex-related genes were identified ( Galindo-Torres et al, 2018 ; Li et al, 2020 ). But as yet, research on the sexual development of simultaneous hermaphroditic mollusks is still in its infancy.…”

Full-Length Transcriptome Sequences Provide Insight Into Hermaphroditism of Freshwater Pearl Mussel Hyriopsis schlegelii

“…A total of 87 candidate genes (1095) reportedly involved the gonad development, sex differences, and sex determination ( Zhang et al, 2014 ; Yatsu et al, 2016 ; Li et al, 2020 ; Zhang et al, 2020 ; Broqurad et al, 2021 ) were present in the full-length gonad transcriptome of 30-month-old H. schlegelii ( Supplementary Table S5 ). Four major sex determination-related genes in mollusks, dmrt-like , sox9 , wnt4 , and fem1 were present in the full-length gonad transcriptome.…”

“…Hermaphroditism occurs during gonadal development of H. schlegelii as in other bivalves, such as Arconaia lanceolata ( Wu et al, 2018 ), Pinctada Margaritifera ( Teaniniuraitemoana et al, 2014 ), Tridacna squamosa ( Li et al, 2020 ), and Crassostrea gigas ( Broquard et al, 2021 ). Hermaphrodite bivalves act as egg-producing females or sperm-producing males at least once in their life cycle.…”