Matsubara Kazumi, Kumazawa Yoshinori, Ota Hidetoshi, Nishida Chizuko, Matsuda Yoichi
Cytogenet Genome Res. 2019;157(1-2):98-106. doi: 10.1159/000496554. Epub 2019 Feb 13.
The suborder Serpentes is divided into 2 infraorders, Scolecophidia and Alethinophidia, which diverged at an early stage of snake diversification. In this study, we examined karyotypes of 4 scolecophidian species (Letheobia simonii, Xerotyphlops vermicularis, Indotyphlops braminus, and Myriopholis macrorhyncha) and performed FISH with 18S-28S rDNA as well as microchromosomal and Z chromosome-linked genes of Elaphe quadrivirgata (Alethinophidia) to investigate the karyotype evolution in the scolecophidian lineage. Diploid chromosome numbers of X. vermicularis and L. simonii were 30 (16 macrochromosomes and 14 microchromosomes) and 32 (16 macrochromosomes and 16 microchromosomes), respectively. The karyotype of a female M. macrorhyncha consisted of 15 macrochromosomes and 19 microchromosomes, including a heterochromatic microchromosome, indicating the presence of a heteromorphic chromosome pair. E. quadrivirgata Z-linked genes mapped to chromosome 4 of M. macrorhyncha, not to the heteromorphic pair. Therefore, M. macrorhyncha may have differentiated ZW sex chromosomes which are not homologous to those of E. quadrivirgata. One of the E. quadrivirgata microchromosomal genes mapped to the terminal region of chromosome 4q in X. vermicularis, suggesting that fusions between microchromosomes and macrochromosomes occurred in this species. rDNA was localized in different macrochromosomal pairs in the 2 diploid scolecophidian snakes examined here, whereas the gene location in a microchromosomal pair was conserved in 5 alethinophidian species examined. These results might imply the occurrence of chromosome fusions in the scolecophidian lineages. In I. braminus, a unique parthenogenetic snake with a triploid karyotype (21 macrochromosomes and 21 microchromosomes), morphological heteromorphisms were identified in chromosomes 1 and 7. Such heteromorphisms in 2 chromosomes were also observed in individuals from distant locations in the broad distribution range of this species, suggesting that the heteromorphisms were fixed in the genome at an early stage of its speciation.
蛇亚目分为2个下目，即盲蛇下目和真蛇下目，它们在蛇类多样化的早期阶段就已分化。在本研究中，我们检测了4种盲蛇下目物种（西蒙细盲蛇、蠕纹盲蛇、婆罗门盲蛇和大吻盲蛇）的核型，并使用18S - 28S rDNA以及红点锦蛇（真蛇下目）的微染色体和Z染色体连锁基因进行荧光原位杂交，以研究盲蛇下目谱系中的核型进化。蠕纹盲蛇和西蒙细盲蛇的二倍体染色体数分别为30（16条大染色体和14条微染色体）和32（16条大染色体和16条微染色体）。雌性大吻盲蛇的核型由15条大染色体和19条微染色体组成，包括一条异染色质微染色体，表明存在一对异形染色体。红点锦蛇的Z连锁基因定位于大吻盲蛇的第4号染色体上，而非异形染色体对。因此，大吻盲蛇可能具有与红点锦蛇不同源的分化的ZW性染色体。红点锦蛇的一个微染色体基因定位于蠕纹盲蛇第4q号染色体的末端区域，这表明该物种发生了微染色体与大染色体之间的融合。rDNA定位于此处检测的2种二倍体盲蛇下目蛇类的不同大染色体对中，而在检测的5种真蛇下目物种中，微染色体对中的基因定位是保守的。这些结果可能意味着盲蛇下目谱系中发生了染色体融合。在婆罗门盲蛇中，这是一种具有三倍体核型（21条大染色体和21条微染色体）的独特孤雌生殖蛇类，在第1号和第7号染色体上鉴定出了形态异形性。在该物种广泛分布范围内来自遥远地点的个体中也观察到了这2条染色体上的这种异形性，这表明这种异形性在其物种形成的早期阶段就已在基因组中固定下来。
