Abstract
Polyploidy occurs naturally in fish; however, the appearance of these species is an occasional and gradual process, which makes it difficult to trace the changes in phenotypes, genotypes, and regulation of gene expression. The allotetraploid hybrids (4nAT) of red crucian carp (RCC; ♀) × common carp (CC; ♂) generated from interspecies crossing are a good model to investigate the initial changes after allopolyploidization. In the present study, we focused on the changes in the active sites of the testicular transcriptome of the allotetraploid by localization of RNA Pol II CTD YSPTSPS (phospho S5) using immunofluorescence and RNA-seq data via bioinformatic analysis. The results showed that there was no significant difference in signal counts of the RNA Pol II CTD (S5) between the different types of fish at the same stages, including RCC, CC, 2nF1, and 4nAT, which means that the number of transcriptionally active sites on germ cell chromosomes was not affected by the increase in chromosome number. Similarly, RNA-seq analysis indicated that in the levels of chromosomes and 10-kb regions in the genome, there were no significant changes in the highly active sites in RCC, 2nF1, and 4nAT. These findings suggest that at the beginning of tetraploid origin, the active transcriptome site of 4nAT in the testis was conserved in the regions of the genome compared to that in RCC and 2nF1. In conclusion, 4nAT shared a similar gene expression model in the regions of the genome with RCC and 2nF1 with significantly different expression levels.
Highlights
Polyploidization refers to the addition of one or more complete sets of chromosomes to the genome (Song et al, 2012; Wang et al, 2019)
Immunofluorescence analysis confirmed that RNA Pol II carboxy terminal domain (CTD) (S5) was expressed in the nuclei of spermatocytes at different stages, with the positive signals varying in number
Small RNA Pol II CTD (S5) agglomerates and accumulations were detected during the prophase of meiosis I, and the number of signals decreased during the meiotic process and completely disappeared in sperm
Summary
Polyploidization refers to the addition of one or more complete sets of chromosomes to the genome (Song et al, 2012; Wang et al, 2019). In allotetraploid red crucian carp ♀ (Carassius auratus red var., abbreviated RCC) × common carp ♂ (Cyprinus carpio L., abbreviated CC), numerous chimeric genes and mutations were found, suggesting genomic incompatibilities that participate in the regulation of transcriptional changes (Liu et al, 2016). These variations in the genome contribute to transcriptome changes in allotetraploids. To date, there is still a lack of global information about the transcriptional activities of fish with polyploidization, on the highly active sites at the genome level
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