Department of Biology and Biotechnology, University of Pavia, Pavia, Italy.
Department of Biotechnology, Faculty of Science, Mahidol University, Bangkok, Thailand.
BMC Genet. 2020 Dec 18;21(Suppl 2):125. doi: 10.1186/s12863-020-00938-z.
The Oriental fruit fly, Bactrocera dorsalis, is a highly polyphagous invasive species with a high reproductive potential. In many tropical and subtropical parts of the world it ranks as one of the major pests of fruits and vegetables. Due to its economic importance, genetic, cytogenetic, genomic and biotechnological approaches have been applied to understand its biology and to implement the Sterile Insect Technique, currently a part of area-wide control programmes against this fly. Its chromosome complement includes five pairs of autosomes and the sex chromosomes. The X and Y sex chromosomes are heteromorphic and the highly heterochromatic and degenerate Y harbours the male factor BdMoY. The characterization of the Y chromosome in this fly apart from elucidating its role as primary sex determination system, it is also of crucial importance to understand its role in male biology. The repetitive nature of the Y chromosome makes it challenging to sequence and characterise.
Using Representational Difference Analysis, fluorescent in situ hybridisation on mitotic chromosomes and in silico genome resources, we show that the B. dorsalis Y chromosome harbours transcribed sequences of gyf, (typo-gyf) a homologue of the Drosophila melanogaster Gigyf gene, and of a non-LTR retrotransposon R1. Similar sequences are also transcribed on the X chromosome. Paralogues of the Gigyf gene are also present on the Y and X chromosomes of the related species B. tryoni. Another identified Y-specific repetitive sequence linked to BdMoY appears to be specific to B. dorsalis.
Our random scan of the Y chromosome provides a broad picture of its general composition and represents a starting point for further applicative and evolutionary studies. The identified repetitive sequences can provide a useful Y-marking system for molecular karyotyping of single embryos. Having a robust diagnostic marker associated with BdMoY will facilitate studies on how BdMoY regulates the male sex determination cascade during the embryonic sex-determination window. The Y chromosome, despite its high degeneracy and heterochromatic nature, harbours transcribed sequences of typo-gyf that may maintain their important function in post-transcriptional mRNA regulation. That transcribed paralogous copies of Gigyf are present also on the X and that this genomic distribution is maintained also in B. tryoni raises questions on the evolution of sex chromosomes in Bactrocera and other tephritids.
东方果实蝇是一种高度多食性的入侵物种，具有很强的繁殖能力。在世界上许多热带和亚热带地区，它被列为水果和蔬菜的主要害虫之一。由于其经济重要性，遗传、细胞遗传、基因组和生物技术方法已被应用于了解其生物学特性，并实施不育昆虫技术，目前这是针对这种蝇的区域控制计划的一部分。其染色体组包括五对常染色体和性染色体。X 和 Y 性染色体异型，高度异染色质和退化的 Y 携带雄性因子 BdMoY。除了阐明其作为主要性别决定系统的作用外，该蝇 Y 染色体的特征对于理解其在雄性生物学中的作用也至关重要。Y 染色体的重复性质使其测序和特征分析具有挑战性。
使用代表性差异分析、有丝分裂染色体的荧光原位杂交和计算机基因组资源，我们表明 B. dorsalis Y 染色体上含有转录序列 gyf、（典型 gyf）与果蝇 Gigyf 基因同源的基因，以及非 LTR 逆转录转座子 R1。类似的序列也在 X 染色体上转录。Gigyf 基因的旁系同源物也存在于相关物种 B. tryoni 的 Y 和 X 染色体上。另一个鉴定出的与 BdMoY 相关的 Y 特异性重复序列似乎是 B. dorsalis 特有的。
我们对 Y 染色体的随机扫描提供了其一般组成的广泛图景，是进一步应用和进化研究的起点。鉴定出的重复序列可以为单个胚胎的分子核型分析提供有用的 Y 标记系统。与 BdMoY 相关的稳健诊断标记将有助于研究 BdMoY 如何在胚胎性别决定窗口期间调节雄性性别决定级联。尽管 Y 染色体高度退化和异染色质化，但它仍含有转录的典型 gyf 序列，这可能使其在转录后 mRNA 调控中保持重要功能。Gigyf 的转录复制拷贝也存在于 X 染色体上，并且这种基因组分布在 B. tryoni 中也得到了维持，这引发了关于 Bactrocera 和其他桔小实蝇科性染色体进化的问题。
