The Sterility of Allotriploid Fish and Fertility of Female Autotriploid Fish

Unambiguous chromosome identification reveals the factors impacting irregular chromosome behaviors in allotriploid AAC Brassica

KEY MESSAGE

The major irregular chromosome pairing and mis-segregation were detected during meiosis through unambiguous chromosome identification and found that allotriploid Brassica can undergo meiosis successfully and produce mostly viable aneuploid gametes. Triploids have played a crucial role in the evolution of species by forming polyploids and facilitating interploidy gene transfer. It is widely accepted that triploids cannot undergo meiosis normally and predominantly produce nonfunctional aneuploid gametes, which restricts their role in species evolution. In this study, we demonstrated that natural and synthetic allotriploid Brassica (AAC), produced by crossing natural and synthetic Brassica napus (AACC) with Brassica rapa (AA), exhibits basically normal chromosome pairing and segregation during meiosis. Homologous A chromosomes paired faithfully and generally segregated equally. Monosomic C chromosomes were largely retained as univalents and randomly entered daughter cells. The primary irregular meiotic behaviors included associations of homoeologs and 45S rDNA loci at diakinesis, as well as homoeologous chromosome replacement and premature sister chromatid separation at anaphase I. Preexisting homoeologous arrangements altered meiotic behaviors in both chromosome irregular pairing and mis-segregation by increasing the formation of A-genomic univalents and A-C bivalents, as well as premature sister chromatid separation and homologous chromosome nondisjunction. Meiotic behaviors depended significantly on the genetic background and heterozygous homoeologous rearrangement. AAC triploids mainly generated aneuploid gametes, most of which were viable. These results demonstrate that allotriploid Brassica containing an intact karyotype can proceed through meiosis successfully, broadening our current understanding of the inheritance and role in species evolution of allotriploid.

Investigation of Sexes and Fertility Potential of Female Russian Sturgeon (Acipenser gueldenstaedtii) and Male American Paddlefish (Polyodon spathula) Hybrids

In the present study, 10 allotriploid (3nALT) and 10 allopentaploid (5nALP) six-month-old hybrid fish and two 3nALT and four 5nALP 40-month-old hybrid fish, which resulted by crossing female Russian sturgeon Acipenser gueldenstaedtii (Brandt and Ratzeberg, 1833) and male American paddlefish Polyodon spathula (Walbaum, 1792), were investigated. It was revealed that six-month-old 3nALT and 5nALP hybrids initially had "undifferentiated" gonads, while in the 40-month-old hybrids, only testes were observed in one case of 3nALT and one case of 5nALP hybrids. The testis of 3nALT hybrids was partially developed with spermatogonia, while the testis of one 5nALP hybrid was in the second developmental stage with low spermatogonia density. We could not determine gonad differentiation in any of the cases when the hybrid individuals had the W sex chromosome. We concluded that the gonad differentiation of these interfamilial hybrids follows a similar pattern to interspecific hybrids of different ploidy parent species of the family Acipenseridae, which is consistent with the classical Haldane's rule. However, it cannot be excluded that the testis of this/these hybrid(s) may produce fertile sperm after sexual maturity, depending on additional genetic, hormonal and environmental factors, and further research is required for its evaluation.

Maternal ploidy shapes reproductive pathways in the triploid hybrid Chrosomus eos × eos-neogaeus

Elements transferred from a mother to her eggs may strongly influence the phenotype of her offspring. Such maternal effects depend on the genotype of the mother, and while multiple ploidy levels occur naturally in some vertebrate species, studies evaluating the impact of maternal ploidy on offspring are scarce. This paper aimed to test whether maternal ploidy is responsible for the two reproductive phenotypes observed in the triploid fish Chrosomus eos × eos-neogaeus. Indeed, these hybrids have two different maternal origins (diploid or triploid) and display two reproductive phenotypes, ameiotic and meiotic hybridogenesis, resulting in diploid and haploid eggs, respectively. To this end, we first conducted a genomic survey to identify epigenetic variations in triploid larvae reared under common garden conditions, concordantly with their maternal origin. The results revealed that the polymorphic epigenetic loci of the larvae clustered into two highly distinct groups consistently with the ploidy of their mother. Diagnostic epigenetic loci were then tested in triploid adult females whose reproductive pathways were already known, to infer their own maternal origin. Altogether, the results suggest that triploid larvae from diploid and triploid mothers will develop the ameiotic and meiotic hybridogenesis pathway, respectively. This confirms that the development of a given reproductive pathway in triploid females results from the ploidy of their mother. Overall, this study supports a strong maternal effect, introducing maternal ploidy and reproductive pathways as additional cause and effect of maternal effects, respectively.

Formation of Different Polyploids Through Disrupting Meiotic Crossover Frequencies Based on cntd1 Knockout in Zebrafish

Polyploidy, a significant catalyst for speciation and evolutionary processes in both plant and animal kingdoms, has been recognized for a long time. However, the exact molecular mechanism that leads to polyploid formation, especially in vertebrates, is not fully understood. Our study aimed to elucidate this phenomenon using the zebrafish model. We successfully achieved an effective knockout of the cyclin N-terminal domain containing 1 (cntd1) using CRISPR/Cas9 technology. This resulted in impaired formation of meiotic crossovers, leading to cell-cycle arrest during meiotic metaphase and triggering apoptosis of spermatocytes in the testes. Despite these defects, the mutant (cntd1-/-) males were still able to produce a limited amount of sperm with normal ploidy and function. Interestingly, in the mutant females, it was the ploidy not the capacity of egg production that was altered. This resulted in the production of haploid, aneuploid, and unreduced gametes. This alteration enabled us to successfully obtain triploid and tetraploid zebrafish from cntd1-/- and cntd1-/-/- females, respectively. Furthermore, the tetraploid-heterozygous zebrafish produced reduced-diploid gametes and yielded all-triploid or all-tetraploid offspring when crossed with wild-type (WT) or tetraploid zebrafish, respectively. Collectively, our findings provide direct evidence supporting the crucial role of meiotic crossover defects in the process of polyploidization. This is particularly evident in the generation of unreduced eggs in fish and, potentially, other vertebrate species.

Formation of autotriploid Carassius auratus and its fertility-related genes analysis

Background

Formation of triploid organism is useful in genetics and breeding. In this study, autotriploid Carassius auratus (3nRR, 3n = 150) was generated from Carassius auratus red var. (RCC, 2n = 100) (♀) and autotetraploid Carassius auratus (4nRR, 4n = 200) (♂). The female 3nRR produced haploid, diploid and triploid eggs, whereas the male 3nRR was infertile. The aim of the present study was to explore fertility of potential candidate genes of 3nRR.

Results

Gonadal transcriptome profiling of four groups (3 females RCC (FRCC), 3 males 4nRR (M4nRR), 3 males 3nRR (M3nRR) and 3 females 3nRR (F3nRR)) was performed using RNA-SEq. A total of 78.90 Gb of clean short reads and 24,262 differentially expressed transcripts (DETs), including 20,155 in F3nRR vs. FRCC and 4,107 in M3nRR vs. M4nRR were identified. A total of 106 enriched pathways were identified through KEGG enrichment analysis. Out of the enriched pathways, 44 and 62 signalling pathways were identified in F3nRR vs. FRCC and M3nRR vs. M4nRR, respectively. A total of 80 and 25 potential candidate genes for fertility-related in F3nRR and M3nRR were identified, respectively, through GO, KEGG analyses and the published literature. Moreover, protein-protein interaction (PPI) network construction of these fertility-associated genes were performed. Analysis of the PPI networks showed that 6 hub genes (MYC, SOX2, BMP4, GATA4, PTEN and BMP2) were involved in female fertility of F3nRR, and 2 hub genes (TP53 and FGF2) were involved in male sterility of M3nRR.

Conclusions

Establishment of autotriploid fish offers an ideal model to study reproductive traits of triploid fish. RNA-Seq data revealed 6 genes, namely, MYC, SOX2, BMP4, GATA4, PTEN and BMP2, involved in the female fertility of the F3nRR. Moreover, 2 genes, namely, TP53 and FGF2, were related to the male sterility of the M3nRR. These findings provide information on reproduction and breeding in triploid fish.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07753-5.

Sox Gene Family Revealed Genetic Variations in Autotetraploid Carassius auratus

The Sox gene family encoded transcription factors that played key roles in developmental processes in vertebrates. To further understand the evolutionary fate of the Sox gene family in teleosts, the Sox genes were comprehensively characterized in fish of different ploidy levels, including blunt snout bream (2n = 48, Megalobrama amblycephala, BSB), goldfish (2n = 100, Carassius auratus red var., 2nRCC), and autotetraploid C. auratus (4n = 200, 4nRCC). The 4nRCC, which derived from the whole genome duplication (WGD) of 2nRCC, were obtained through the distant hybridization of 2nRCC (♀) × BSB (♂). Compared with the 26 Sox genes in zebrafish (2n = 50, Danio rerio), 26, 47, and 92 putative Sox genes were identified in the BSB, 2nRCC, and 4nRCC genomes, respectively, and classified into seven subfamilies (B1, B2, C, D, E, F, and K). Comparative analyses showed that 89.36% (42/47) of Sox genes were duplicated in 2nRCC compared with those in BSB, while 97.83% (90/92) of Sox genes were duplicated in 4nRCC compared with those in 2nRCC, meaning the Sox gene family had undergone an expansion in BSB, 2nRCC, and 4nRCC, respectively, following polyploidization events. In addition, potential gene loss, genetic variations, and paternal parent SNP locus insertion occurred during the polyploidization events. Our data provided new insights into the evolution of the Sox gene family in polyploid vertebrates after several rounds of WGD events.

Bisexual Fertile Triploid Zebrafish (Danio rerio): a Rare Case

Previous studies have suggested that artificially induced triploid zebrafish are exclusively male-biased. Owing to greatly inhibited gonadal development for the artificially induced triploid fish, they are regarded to be sterile in general. In this article, partially fertile bisexual triploid zebrafish are produced by suppressing extrusion of the second polar body by heat shock. Histological observation confirms that the early gonadal development of these triploid zebrafish is normal. Backcrossing and self-crossing are used to demonstrate that both the female and male triploid zebrafish have partial reproductive ability. Their dynamic of chromosomes during meiosis is revealed from the chromosome preparations of gonads. Examination of the expressed gonadal development-related genes shows some molecular evidence of the normal gonadal development in the triploid zebrafish. Clearly, these fertile bisexual triploid zebrafish can provide a unique system to study sex determination, as well as aneuploidy associated human diseases such as infertility and pregnancy loss.

Optimization Techniques to Deeply Mine the Transcriptomic Profile of the Sub-Genomes in Hybrid Fish Lineage

It has been shown that reciprocal cross allodiploid lineage with sub-genomes derived from the cross of Megalobrama amblycephala (BSB) × Culter alburnus (TC) generates the variations in phenotypes and genotypes, but it is still a challenge to deeply mine biological information in the transcriptomic profile of this lineage owing to its genomic complexity and lack of efficient data mining methods. In this paper, we establish an optimization model by non-negative matrix factorization approach for deeply mining the transcriptomic profile of the sub-genomes in hybrid fish lineage. A new so-called spectral conjugate gradient algorithm is developed to solve a sequence of large-scale subproblems such that the original complicated model can be efficiently solved. It is shown that the proposed method can provide a satisfactory result of taxonomy for the hybrid fish lineage such that their genetic characteristics are revealed, even for the samples with larger detection errors. Particularly, highly expressed shared genes are found for each class of the fish. The hybrid progeny of TC and BSB displays significant hybrid characteristics. The third generation of TC-BSB hybrid progeny (BTF3 and TBF3) shows larger trait separation.