Johnson Pokorná Martina, Rovatsos Michail, Kratochvíl Lukáš
Department of Ecology, Faculty of Science, Charles University in Prague, Praha, Czech Republic; Institute of Animal Physiology and Genetics, Academy of the Sciences of the Czech Republic, Liběchov, Czech Republic.
Department of Ecology, Faculty of Science, Charles University in Prague, Praha, Czech Republic.
PLoS One. 2014 Aug 13;9(8):e104716. doi: 10.1371/journal.pone.0104716. eCollection 2014.
A wide variety of sex determination systems exist among squamate reptiles. They can therefore serve as an important model for studies of evolutionary transitions among particular sex determination systems. However, we still have only a limited knowledge of sex determination in certain important lineages of squamates. In this respect, one of the most understudied groups is the family Helodermatidae (Anguimorpha) encompassing the only two venomous species of lizards which are potentially lethal to human beings. We uncovered homomorphic ZZ/ZW sex chromosomes in the Gila monster (Heloderma suspectum) with a highly heterochromatic W chromosome. The sex chromosomes are morphologically similar to the ZZ/ZW sex chromosomes of monitor lizards (Varanidae). If the sex chromosomes of helodermatids and varanids are homologous, female heterogamety may be ancestral for the whole Anguimorpha group. Moreover, we found that the karyotype of the Gila monster consists of 2n = 36 chromosomes (14 larger metacentric chromosomes and 22 acrocentric microchromosomes). 2n = 36 is the widely distributed chromosomal number among squamates. In his pioneering works representing the only previous cytogenetic examination of the family Helodermatidae, Matthey reported the karyotype as 2n = 38 and suggested a different chromosomal morphology for this species. We believe that this was probably erroneously. We also discovered a strong accumulation of telomeric sequences on several pairs of microchromosomes in the Gila monster, which is a trait documented relatively rarely in vertebrates. These new data fill an important gap in our understanding of the sex determination and karyotype evolution of squamates.
有鳞目爬行动物存在多种性别决定系统。因此，它们可作为研究特定性别决定系统之间进化转变的重要模型。然而，我们对某些重要有鳞目谱系的性别决定仍然知之甚少。在这方面，研究最少的群体之一是毒蜥科（美洲鬣蜥亚目），该科包含仅有的两种对人类有潜在致命危险的有毒蜥蜴物种。我们在吉拉毒蜥（希拉毒蜥）中发现了同形的ZZ/ZW性染色体，其中W染色体高度异染色质化。这些性染色体在形态上与巨蜥科（巨蜥科）的ZZ/ZW性染色体相似。如果毒蜥科和巨蜥科的性染色体是同源的，那么雌性异配性别可能是整个美洲鬣蜥亚目群体的祖先特征。此外，我们发现吉拉毒蜥的核型由2n = 36条染色体组成（14条较大的中着丝粒染色体和22条近端着丝粒微染色体）。2n = 36是有鳞目动物中广泛分布的染色体数目。在Matthey的开创性著作中，这是对毒蜥科此前唯一的细胞遗传学研究，他报道该物种的核型为2n = 38，并提出了不同的染色体形态。我们认为这可能是错误的。我们还在吉拉毒蜥的几对微染色体上发现了端粒序列的强烈积累，这是脊椎动物中相对罕见的一种特征。这些新数据填补了我们在理解有鳞目动物性别决定和核型进化方面的一个重要空白。
