Karyotype Reorganization in the Hokou Gecko (Gekko hokouensis, Gekkonidae): The Process of Microchromosome Disappearance in Gekkota

RESEARCH ARTICLE Karyotype Reorganization in the Hokou Gecko (Gekko hokouensis, Gekkonidae): The Process of Microchromosome Disappearance in Gekkota Kornsorn Srikulnath1,2,3*, Yoshinobu Uno1, Chizuko Nishida4, Hidetoshi Ota5, Yoichi Matsuda1* 1 Laboratory of Animal Genetics, Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, Japan, 2 Laboratory of Animal Cytogenetics and Comparative Genomics, Department of Genetics, Faculty of Science, Kasetsart University, 50 Ngamwongwan, Chatuchak, Bangkok, Thailand, 3 Center for Advanced Studies in Tropical Natural Resources, National Research University-Kasetsart University (CASTNAR, NRU-KU), Kasetsart University, Bangkok, Thailand, 4 Department of Natural History Sciences, Faculty of Science, Hokkaido University, Kita 10, Nishi 8, Kita-ku, Sapporo, Hokkaido, Japan, 5 Institute of Natural and Environmental Sciences, University of Hyogo, and Museum of Nature and Human Activities, Sanda, Hyogo, Japan * (YM); (KS) OPEN ACCESS Citation: Srikulnath K, Uno Y, Nishida C, Ota H, Matsuda Y (2015) Karyotype Reorganization in the Hokou Gecko (Gekko hokouensis, Gekkonidae): The Process of Microchromosome Disappearance in Gekkota. PLoS ONE 10(8): e0134829. doi:10.1371/ journal.pone.0134829 Editor: Roscoe Stanyon, University of Florence, ITALY Received: June 9, 2015 Accepted: July 15, 2015 Published: August 4, 2015 Copyright: © 2015 Srikulnath et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Abstract The Hokou gecko (Gekko hokouensis: Gekkonidae, Gekkota, Squamata) has the chromosome number 2n = 38, with no microchromosomes. For molecular cytogenetic characterization of the gekkotan karyotype, we constructed a cytogenetic map for G. hokouensis, which retains the ancestral karyotype of Gekkota, with 86 functional genes, and compared it with cytogenetic maps for four Toxicofera species that have many microchromosomes (Elaphe quadrivirgata, Varanus salvator macromaculatus, Leiolepis reevesii rubritaeniata, and Anolis carolinensis) and that for a lacertid species (Lacerta agilis) with only one pair of autosomal microchromosomes. Ten pairs of G. hokouensis chromosomes [GHO1, 2, 3, Z(4), 6, 7, 8, 13, 14, and 15] showed highly conserved linkage homology with macrochromosomes and/or macrochromosome arms of the four Toxicofera species and corresponded to eight L. agilis macrochromosomes (LAG). However, GHO5, GHO9, GHO10, GHO11, and LAG6 were composed of chromosome segments that have a homology with Toxicofera microchromosomes, and no homology was found in the chromosomes between G. hokouensis and L. agilis. These results suggest that repeated fusions of microchromosomes may have occurred independently in each lineage of Gekkota and Lacertidae, leading to the disappearance of microchromosomes and appearance of small-sized macrochromosomes. Data Availability Statement: All relevant data are within the paper. Funding: This study was supported by Grants-in-Aid for Scientific Research on Innovative Areas (No. 23113004) and Scientific Research (B) (No. 22370081) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Introduction Karyotypes of non-avian reptiles have been extensively diversified [1] since Sauropsida (all existing reptiles and birds) diverged from Synapsida around 320 million years ago (MYA) [2]. Generally, turtles have many microchromosomes, which are designated by their chromosome PLOS ONE | DOI:10.1371/journal.pone.0134829 August 4, 2015 1 / 19 Karyotypic Reorganization in Gekko hokouensis (Gekkonidae) Competing Interests: The authors have declared that no competing interests exist. morphologies as dot-shaped chromosomes whose centromere positions are undetectable [3, 4], whereas all crocodilian species lack microchromosomes. Crocodilians show low karyotypic variation with respect to both chromosome number (chromosome arm number in particular) and chromosome morphology [1, 5]. In squamate reptiles, both macrochromosomes and microchromosomes are commonly found in Scincoidea and Episquamata exclusive of Lacertidae; in contrast, only a few or no microchromosomes are found in Lacertidae and Gekkota [1, 6]. Until recently, not much information was available on the process of chromosomal reorganization, which causes extensive karyotypic variation in reptiles, such as appearance or disappearance of microchromosomes. However, recent comparative gene mapping of several nonavian reptile species (Pelodiscus sinensis, Testudines; Crocodylus siamensis, Crocodilia; Lacerta agilis, Elaphe quadrivirgata, Varanus salvator macromaculatus, Leiolepis reevesii rubritaeniata, Pogona vitticeps, and Anolis carolinensis, Episquamata) with the chicken revealed the extensive homology between avian and reptilian chromosomes and suggested that the common ancestor of amniotes may have had many microchromosomes, whose linkages have been conserved between the chicken and reptiles [7–16]. In squamate reptiles, however, microchromosomes, supposedly occurring in large number in the ancestral state, are considered to have reduced because of their fusions with macrochromosomes and/or with other microchromosomes [9–13, 15]. Lacertid lizards of the superfamily Lacertoidea are classified into Episquamata that generally have many microchromosomes [1, 6, 17]; nevertheless, karyotypes of lacertid lizards include few or no microchromosomes [1, 18–22]. Comparative mapping of 86 functional genes in L. agilis revealed that linkage groups of chromosomes are highly conserved between L. agilis and Toxicofera species (V. salvator macromaculatus, Anguimorpha; L. reevesii rubritaeniata, Iguania; and E. quadrivirgata, Serpentes), whose karyotypes consist of macrochromosomes and many indistinguishable microchromosomes [9–13]. This finding suggests that the karyotypes of lacertid lizards probably have resulted from repeated fusions of microchromosomes, leading to the scarcity or complete absence of these elements. Gekkota, which includes seven families (Diplodactylidae, Carphodactylidae, Pigopodidae, Eublepharidae, Sphaerodactylidae, Gekkonidae, and Phyllodactylidae), is phylogenetically located at the base of squamate reptiles exclusive of the Dibamidae, being estimated to have diverged from the common ancestor of non-dibamid squamates around 170–240 MYA [1, 6, 23, 24]. This phylogenetic relationship suggests that geckos may retain the ancestral squamate karyotypes. Notwithstanding this, however, geckos actually have unique karyotypes that are also characterized by scarcity of microchromosomes with a very few exceptions [25], as observed in lac (...truncated)