Evidence for the evolutionary nascence of a novel sex determination pathway in honeybees
Evidence for the evolutionary nascence of a novel sex determination pathway in honeybees
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DOI：
10.1038/nature07052
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发表时间：
2008-07-24
期刊：
影响因子：
64.8
通讯作者：
Beye, Martin
中科院分区：
文献类型：
--
作者：
Hasselmann, Martin;Gempe, Tanja;Beye, Martin
蜜蜂（Apis mellifera）的性别决定由携带互补性别决定基因（csd）的单个基因座的杂合性控制（1），这与已得到充分研究的果蝇性染色体系统相反（2）。在csd上杂合子的蜜蜂是雌性，而纯合子和半合子（单倍体个体）是雄性。虽然在自然界中至少有15种不同的csd等位基因是已知的（3），但将等位基因相互作用与性发育程序转换联系起来的机制仍然不清楚。在这里，我们报告了蜜蜂性别决定途径的一个新的组成部分，编码csd上游的12个酶。feminizer（fem）基因是csd产生的祖先保守的祖基因，编码SR型蛋白，具有富含Arg/Ser的结构域。Fem与果蝇的主要性别决定基因Transformer（tra）具有相同的精氨酸/丝氨酸和脯氨酸富集结构域排列，但缺乏保守基序，除了Fem仅与另一种果蝇Ceratitis capitata的Tra共享的30个氨基酸基序（4）。像tra一样，fem转录本也是选择性剪接的。男性特异性剪接变体包含提前终止密码子并且不产生功能性产物，而女性特异性剪接变体编码功能性蛋白。我们表明，RNA干扰（RNAi）诱导敲除的女性特定的fem剪接变异体的结果在雄蜂，表明fem产品是需要整个女性的发展。此外，RNAi诱导的雌性等位基因csd转录物的敲除导致雄性特异性fem剪接变体，表明fem基因实现了由csd处的杂合性控制的发育途径的转换。对五种蜜蜂fem和csd编码序列的比较分析表明，csd在蜜蜂谱系中最近起源于fem祖先，并为csd的正选择伴随着fem的纯化选择提供了证据。蜜蜂的fem基因座揭示了基因复制和正选择作为一种新的性别决定途径起源的进化机制。
Sex determination in honeybees (Apis mellifera) is governed by heterozygosity at a single locus harbouring the complementary sex determiner (csd) gene(1), in contrast to the well-studied sex chromosome system of Drosophila melanogaster(2). Bees heterozygous at csd are females, whereas homozygotes and hemizygotes (haploid individuals) are males. Although at least 15 different csd alleles are known among natural bee populations(3), the mechanisms linking allelic interactions to switching of the sexual development programme are still obscure. Here we report a new component of the sex-determining pathway in honeybees, encoded 12 kilobases upstream of csd. The gene feminizer (fem) is the ancestrally conserved progenitor gene from which csd arose and encodes an SR-type protein, harbouring an Arg/Ser-rich domain. Fem shares the same arrangement of Arg/Ser- and proline-rich-domain with the Drosophila principal sex-determining gene transformer (tra), but lacks conserved motifs except for a 30-amino-acid motif that Fem shares only with Tra of another fly, Ceratitis capitata(4). Like tra, the fem transcript is alternatively spliced. The male-specific splice variant contains a premature stop codon and yields no functional product, whereas the female-specific splice variant encodes the functional protein. We show that RNA interference (RNAi)-induced knockdowns of the female-specific fem splice variant result in male bees, indicating that the fem product is required for entire female development. Furthermore, RNAi- induced knockdowns of female allelic csd transcripts result in the male-specific fem splice variant, suggesting that the fem gene implements the switch of developmental pathways controlled by heterozygosity at csd. Comparative analysis of fem and csd coding sequences from five bee species indicates a recent origin of csd in the honeybee lineage from the fem progenitor and provides evidence for positive selection at csd accompanied by purifying selection at fem. The fem locus in bees uncovers gene duplication and positive selection as evolutionary mechanisms underlying the origin of a novel sex determination pathway.