Dmc1 (disrupted meiotic cDNA) is a functionally specific gene, which was firstly discovered in yeast and then found to encode a protein required for homologous chromosome synapsis during the process of meiosis. In this investigation, we cloned the partial cDNAs of Dmc1 of diploid red crucian carp, Japanese crucian carp, common carp, triploid crucian carp and allotetraploid hybrids by using a pair of degenerate primers based on the conservative sequence of amino acids of the DMC1 protein in yeast, mouse and human. The full length cDNAs were then obtained by rapid amplification of cDNA ends (RACE). Our data showed that the full length cDNAs of Dmc1 in the three diploid fishes are all 1375 bp long, while it is 1383 bp long in triploids and 1379 bp long in allotetraploids. And despite of the variation in length, all the cDNAs encode a protein of 342 amino acids. A high homology of 97.3% of the DMC1 protein can be drawn by comparing the amino acid sequences in the three diploids, which is also of 86%, 86% and 95% similarity to human, mouse and zebrafish, respectively. A comparative study of the expression pattern of Dmc1 was carried out by RT-PCR using specific primers against the same sequences of coding regions in different ploidy cyprinid fishes, from which it was showed that Dmc1 was expressed only in gonads of these five kinds of fishes. The expression pattern of Dmc1 in both ovaries and testes from different ploidy fishes within breeding season was also studied by Real-time PCR, and the results showed that the expression of this gene was greatly different among the three different ploidy fishes, which was the highest of triploid and lowest of allotetraploids. The histological sections data showed matured gonads of both diploid red crucian carp and allotetraploids in breeding season, although the latter demonstrated a higher maturation, and no gonadal maturation could be observed in triploids. In conclusion, we suggest that Dmc1 is specifically expressed in the period of meiosis in all the ploidy cyprinid fishes and directly related with the development of gonad in a manner of ploidy-independent way. And further, the high expression of Dmc1 in female triploids might be associated with abnormal meiosis and sterility.
Crossing the cyprinids diploid blunt snout bream Megalobrama amblycephala (BSB) and Carassius auratus red var. (RCC) generated sterile triploid (3nRB) and fertile tetraploid (4nRB) hybrid offspring. Utilizing inverted terminal repeats (ITRs) of transposon Tdr1 from Danio rerio as PCR primer, the results showed that evident change in the number of Tc1-like transposons in 4nRB relative to BSB occurred, whereas such change did not arise in 3nRB compared to BSB. No Tc1-like transposon was found in RCC. A novel transposon was isolated from both BSB and 3nRB and designated as Tma1, which consisted of multiple copies after dot-blot hybridization. Based on the analysis of PCR amplified flanking sequence, characterization of Tma1 indicated that this element flanked by a duplicated TA dinucleotide and harbored an ITR of about 224 bp. Tma1 also harbored an incomplete transposase gene. Another novel transposon designated as Tte1 was detected in 4nRB, which harbored an ITR of roughly 130 bp and consisted of multiple copies, but had no transposase gene. The analysis of PCR amplification and Southern blot hybridization showed that DNAs of 4nRB, which were hybridized to DIG-labeled pTma1, did not give band by PCR with Tma1 primer, on the other hand, 7 of 15 DNA samples from BSB, which were hybridized to DIG-labeled pTte1, did not produce band by PCR with Tte1 primer. These results suggest that Tte1 may be a recent invasion in BSB population and burst in 4nRB offspring. Our data provide clues as to the possible role of transposons as a driving mechanism for genomic evolution.
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