Ruiz-Rejon, C. | bioRxiv Science

bioRxiv2025

Impaired Sertoli-Spermatogonia Interactions Contribute to Oligospermia and Infertility in F1 Captive-bred Male Solea senegalensis

Reproductive dysfunction of captive-bred males of the Senegalese sole (Solea senegalensis) represents a significant bottleneck for its aquaculture, as these fish exhibit reduced sperm production and impaired fertility compared to wild-bred counterparts acclimated to farm conditions. To elucidate the cellular and molecular mechanisms underlying this phenomenon, single-nuclei RNA sequencing was performed on gonadal tissue from adult captive-bred and wild-bred males. The analysis yielded a high-quality dataset comprising [~]80.000 cells, which were grouped into eleven distinct clusters representing all major germline and somatic cell types, including spermatogonial stem cells, differentiating spermatogonia, spermatocytes, spermatids, Sertoli cells, Leydig cells, immune cells, and peritubular myoid cells. It is noteworthy that captive-bred males exhibited a marked overrepresentation of proliferative spermatogonia and a significant reduction in mature spermatids, suggesting a disruption in the progression of spermatogenesis. Differential expression and functional enrichment analyses revealed that spermatogonial cells in captive-bred males displayed heightened translational activity alongside downregulation of pathways related to cell-cell communication and interaction. Focused cell-cell communication analyses further indicated defective Sertoli-spermatogonia interactions as a key factor contributing to oligospermia and infertility of captive-bred males. This study provides the first single-nuclei transcriptomic atlas of the Senegalese sole male gonad, offering valuable insights into the molecular basis of reproductive failure in captivity related to gonadal development. The findings of the study will inform future strategies to enhance selective breeding and improve aquaculture productivity for this economically important species.

genomics↗

bioRxiv2022

A chromosome-level genome assembly enables the identification of the follicle stimulating hormone receptor as the master sex determining gene in Solea senegalensis

Sex determination (SD) mechanisms are exceptionally diverse and show high evolutionary rates in fish. Pleuronectiformes is an emblematic fish group characterized by its adaptation to demersal life and its compact genomes. Here, we present a chromosome-level genome assembly of Senegalese sole, a promising European aquaculture species. We combined long- and short-read sequencing and a highly dense genetic map to obtain a contiguous assembly of 613 Mb (N50 = 29.0 Mb, 99% of the assembly in the n = 21 chromosomes of its karyotype). The correspondence between this new assembly and the Senegalese sole chromosomes was established by fluorescence in situ hybridization with BAC probes. Orthology within Pleuronectiformes was assessed by using the chromosome-level genomes of six important commercial flatfishes covering a broad phylogenetic spectrum of the order. A total of 7936 single-gene orthologues, shared by the six species, were used to identify syntenies in Pleuronectiformes and to explore chromosome evolutionary patterns in the order. Whole genome resequencing of six males and six females enabled the identification of 41 fixed allelic variants in the follicle stimulating hormone receptor (fshr) gene, homozygous in females and heterozygous in males, consistent with an XX / XY chromosome system. The observed association between fshr SNPs and sex was confirmed at the species level in a broad sample, which allowed tuning up a molecular sexing tool. Fshr demonstrated differential gene expression between male and female gonads since 86 days post-fertilization, when the gonad was still an undifferentiated primordium, concomitant with the activation of other testis and ovary marker genes, such as amh and cyp19a1a genes, respectively. Interestingly, the Y-linked fshr allele, which included 24 non-synonymous variants, expressed to a higher level than the X-linked allele at all stages. We hypothesize a molecular mechanism hampering the action of the follicle stimulating hormone that would drive the undifferentiated gonad toward testis.

genomics↗