Nurminsky D I, Nurminskaya M V, De Aguiar D, Hartl D L
Harvard University, Department of Organismic & Evolutionary Biology, Cambridge, Massachusetts 02138, USA.
Nature. 1998 Dec 10;396(6711):572-5. doi: 10.1038/25126.
The pattern of genetic variation across the genome of Drosophila melanogaster is consistent with the occurrence of frequent 'selective sweeps', in which new favourable mutations become incorporated into the species so quickly that linked alleles can 'hitchhike' and also become fixed. Because of the hitchhiking of linked genes, it is generally difficult to identify the target of any putative selective sweep. Here, however, we identify a new gene in D. melanogaster that codes for a sperm-specific axonemal dynein subunit. The gene has a new testes-specific promoter derived from a protein-coding region in a gene encoding the cell-adhesion protein annexin X (AnnX), and it contains a new protein-coding exon derived from an intron in a gene encoding a cytoplasmic dynein intermediate chain (Cdic). The new transcription unit, designated Sdic (for sperm-specific dynein intermediate chain), has been duplicated about tenfold in a tandem array. Consistent with the selective sweep of this gene, the level of genetic polymorphism near Sdic is unusually low. The discovery of this gene supports other results that point to the rapid molecular evolution of male reproductive functions.
黑腹果蝇基因组中的遗传变异模式与频繁发生的“选择性清除”现象一致，在这种现象中，新的有利突变迅速融入物种，以至于连锁等位基因能够“搭便车”并也被固定下来。由于连锁基因的搭便车效应，通常很难确定任何假定的选择性清除的目标。然而，在这里我们在黑腹果蝇中鉴定出一个新基因，它编码一种精子特异性轴丝动力蛋白亚基。该基因有一个新的睾丸特异性启动子，它源自编码细胞粘附蛋白膜联蛋白X（AnnX）的基因中的一个蛋白质编码区域，并且它包含一个新的蛋白质编码外显子，该外显子源自编码细胞质动力蛋白中间链（Cdic）的基因中的一个内含子。这个新的转录单元，命名为Sdic（精子特异性动力蛋白中间链），已经以串联阵列的形式复制了大约十倍。与该基因的选择性清除一致，Sdic附近的遗传多态性水平异常低。这个基因的发现支持了其他指向雄性生殖功能快速分子进化的结果。
