Abstract
Triploid is usually considered to be unable to perform normal meiosis due to the abnormal behavior of the three sets of chromosomes. But autotriploid Carassius auratus in the Dongting water system (3n = 150, abbreviated as 3nCC) can perform normal meiosis. In artificial autotriploid Carassius auratus (3n = 150, abbreviated as 3nRR), female individuals undergo normal meiosis and produce mature gametes, while male individuals cannot. To better understand the effects of triploidization on meiosis in fish, we study the structure, methylation level, and expression level of meiosis-related genes (Dmc1, Ph1) in diploid Carassius auratus (2n = 100, abbreviated as 2nCC), Carassius auratus red var.(2n = 100, abbreviated as RCC), 3nCC and 3nRR. The results show that, compared with their diploid ancestors (2nCC and RCC), Dmc1 and Ph1 genes are hypomethylated in all 3nCC and female 3nRR, while are hypermethylated in male 3nRR. Correspondingly, Dmc1 and Ph1 genes are highly expressed in all 3nCC and female 3nRR, while are lowly expressed in male 3nRR. These results indicate that high expression of meiosis-related genes can contribute to restoration of bivalent pairing during meiosis in autotriploid Carassius auratus. This study provides new insights into the effect of DNA methylation on the fertility in triploid fish.
Highlights
Polyploidization, the addition of a complete set of chromosomes to the genome, represents one of the most dramatic mutations known to occur (Mallet 2007; Otto 2007)
Triploids are traditionally considered sterile (Ramsey and Schemske 2002; Cifuentes et al 2013); recent research revealed that autotriploid fish are can be fertile and can produce normal gametes (Qin et al 2015; Qin et al 2016)
Male 3nRR show a large number of vacuoles and broken sperm cells in the histological sections of the testis, while a normal ovarian structure is found in female individual
Summary
Polyploidization, the addition of a complete set of chromosomes to the genome, represents one of the most dramatic mutations known to occur (Mallet 2007; Otto 2007). Autopolyploids exhibit multivalent pairing during meiosis, in which an additional set (or sets) of chromosomes may originate from the same species (Qin et al 2019). Allopolyploids result from the combination of sets of chromosomes from different species, which undergo bivalent pairing at meiosis because of only a homologous chromosome pair (Qin et al 2014b). DMC1 plays an important role in the exchange of DNA chains between homologous chromosomes and the repair of DSB (DNA double-strand breaks) during meiosis (Chen et al 2016). Ph1 gene allows homologous chromosome pairing to prevent partial homologous chromosome pairing in hybrids and polyploid (Al-Kaff et al 2008)
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