Clonal reproduction assured by sister chromosome pairing in dojo loach, a teleost fish
Wild-type dojo loach (Misgurnus anguillicaudatus) commonly reproduces bisexually as a gonochoristic diploid (2n = 50), but gynogenetically reproducing clonal diploid lines (2n = 50) exist in certain districts in Japan. Clones have been considered to develop from past hybridization event(s) between two genetically diverse groups, A and B, within the species. Fluorescence in situ hybridization analyses using the repetitive sequence “ManDra” as a probe clearly distinguished 25 chromosomes derived from group B out of a total of 50 diploid chromosomes of the clone, providing strong molecular cytogenetic evidence of its hybrid origin. In meiosis, diploid wild-type showed 25 bivalents, while diploid clones revealed 50 bivalents, indicating the presence of 100 chromosomes. In meiotic chromosome spreads in sex-reversed clonal males, ManDra signals were detected in 25 out of 50 bivalents, and only one out of two bivalents possessing major ribosomal RNA coding regions exhibited two positive ManDra signals. In clonal females, ManDra signals were detected in approximately 25 out of 50 bivalents. Thus, unreduced gametes should be generated by the pairing between sister chromosomes doubled from each ancestral chromosome from the different groups by premeiotic endomitosis. Sister chromosome pairing should assure production of unreduced isogenic clonal gametes due to the absence of the influence of recombination or crossing over.
KeywordsClone FISH Hybrid Premeiotic endomitosis Sister chromosome Unreduced gametes
4′, 6-Diamidino-2-phenylindole, dihydrochloride
Fluorescence in situ hybridization
Genomic in situ hybridization
Interphotoreceptor retinoid binding protein 2
Mitochondrial DNA control region
Nucleolar organizing regions
Recombination activating gene 1
Saline sodium citrate buffer
We thank Dr. Atsushi Fujiwara (National Research Institute of Fisheries Science, Japan Fisheries Research and Education Agency) for technical advice. This study was supported by Grants-in-Aid from JSPS (Japan Society for the Promotion of Science) KAKENHI Grant Number 15H02457 and JSPS Research Fellow Number 17J01971.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
Informed consent was obtained from all individual participants included in the study.
This study was performed according to the Guide for the Care and Use of Laboratory Animals at Hokkaido University. All animal experiments were approved by the animal study ethical committee of Hokkaido University (approval number 19-2).
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