Reptiles exhibit a variety of modes of sex determination, including both temperature-dependent and genetic mechanisms. Among those species with genetic sex determination, sex chromosomes of varying heterogamety (XX/XY and ZZ/ZW) have been observed with different degrees of differentiation. Karyotype studies have demonstrated that Gila monsters (Heloderma suspectum) have ZZ/ZW sex determination and this system is likely homologous to the ZZ/ZW system in the Komodo dragon (Varanus komodoensis), but little else is known about their sex chromosomes. Here, we report the assembly and analysis of the Gila monster genome. We generated a de novo draft genome assembly for a male using 10X Genomics technology. We further generated and analyzed short-read whole genome sequencing and whole transcriptome sequencing data for three males and three females. By comparing female and male genomic data, we identified four putative Z-chromosome scaffolds. These putative Z-chromosome scaffolds are homologous to Z-linked scaffolds identified in the Komodo dragon. Further, by analyzing RNAseq data, we observed evidence of incomplete dosage compensation between the Gila monster Z chromosome and autosomes and a lack of balance in Z-linked expression between the sexes. In particular, we observe lower expression of the Z in females (ZW) than males (ZZ) on a global basis, though we find evidence suggesting local gene-by-gene compensation. This pattern has been observed in most other ZZ/ZW systems studied to date and may represent a general pattern for female heterogamety in vertebrates.

中文翻译：

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从头基因组组装揭示ZZ/ZW吉拉毒蜥（Heloderma Shoulderum）缺乏剂量平衡和不完全剂量补偿

爬行动物表现出多种性别决定模式，包括温度依赖性和遗传机制。在那些具有遗传性别决定的物种中，观察到不同异配性（XX/XY和ZZ/ZW）的性染色体具有不同程度的分化。核型研究表明吉拉毒蜥（Heloderma Shoulderum）具有 ZZ/ZW 性别决定系统，该系统可能与科莫多巨蜥（Varanus komodoensis）的 ZZ/ZW 系统同源，但人们对它们的性染色体知之甚少。在这里，我们报告吉拉毒蜥基因组的组装和分析。我们使用 10X Genomics 技术为男性生成了从头基因组组装草案。我们进一步生成并分析了三名男性和三名女性的短读长全基因组测序和全转录组测序数据。通过比较女性和男性基因组数据，我们确定了四种假定的 Z 染色体支架。这些假定的 Z 染色体支架与在科莫​​多巨蜥中发现的 Z 连锁支架同源。此外，通过分析 RNAseq 数据，我们观察到吉拉毒蜥 Z 染色体和常染色体之间不完全剂量补偿以及两性之间 Z 连锁表达缺乏平衡的证据。特别是，我们观察到，在全球范围内，女性 (ZW) 的 Z 表达低于男性 (ZZ)，尽管我们发现证据表明存在局部基因间补偿。这种模式已在迄今为止研究的大多数其他 ZZ/ZW 系统中观察到，并且可能代表脊椎动物雌性异配性的一般模式。