Ranz José María, Ponce Ana Rita, Hartl Daniel L, Nurminsky Dmitry
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 33143, USA.
Genetica. 2003 Jul;118(2-3):233-44.
Sdic is a new gene that evolved recently in the lineage of Drosophila melanogaster. It was formed from a duplication and fusion of the gene AnnX, which encodes annexin X, and Cdic, which encodes the intermediate polypeptide chain of the cytoplasmic dynein. The fusion joins AnnX exon 4 with Cdic intron 3, which brings together three putative promoter elements for testes-specific expression of Sdic: the distal conserved element (DCE) and testes-specific element (TSE) are derived from AnnX, and the proximal conserved element (PCE) from Cdic intron 3. Sdic transcription initiates within the PCE, and translation is initiated within the sequence derived from Cdic intron 3, continuing through a 10 base pair insertion that creates a new splice donor site that enables the new coding sequence derived from intron 3 to be joined with the coding sequence of Cdic exon 4. A novel protein is created lacking 100 residues at the amino end that contain sequence motifs essential for the function of cytoplasmic dynein intermediate chains. Instead, the amino end is a hydrophobic region of 16 residues that resembles the amino end of axonemal dynein intermediate chains from other organisms. The downstream portion of Sdic features large deletions eliminating Cdic exons v2 and v3, as well as multiple frameshift deletions or insertions. The new protein becomes incorporated into the tail of the mature sperm and may function as an axonemal dynein intermediate chain. The new Sdic gene is present in about 10 tandem repeats between the wildtype Cdic and AnnX genes located near the base of the X chromosome. The implications of these findings are discussed relative to the origin of new gene functions and the process of speciation.
Sdic是一种最近在黑腹果蝇谱系中进化出来的新基因。它由AnnX基因（编码膜联蛋白X）和Cdic基因（编码细胞质动力蛋白的中间多肽链）的复制和融合形成。这种融合将AnnX外显子4与Cdic内含子3连接起来，从而汇集了三个用于Sdic睾丸特异性表达的假定启动子元件：远端保守元件（DCE）和睾丸特异性元件（TSE）源自AnnX，近端保守元件（PCE）源自Cdic内含子3。Sdic转录在PCE内起始，翻译在源自Cdic内含子3的序列内起始，并通过一个10个碱基对的插入继续进行，该插入产生了一个新的剪接供体位点，使源自内含子3的新编码序列能够与Cdic外显子4的编码序列连接。由此产生了一种新蛋白质，其氨基端缺少100个残基，这些残基包含细胞质动力蛋白中间链功能所必需的序列基序。相反，氨基端是一个由16个残基组成的疏水区域，类似于其他生物体轴丝动力蛋白中间链的氨基端。Sdic的下游部分有大量缺失，消除了Cdic外显子v2和v3，以及多个移码缺失或插入。这种新蛋白质被整合到成熟精子的尾部，可能作为轴丝动力蛋白中间链发挥作用。新的Sdic基因在位于X染色体基部附近的野生型Cdic和AnnX基因之间以大约10个串联重复的形式存在。相对于新基因功能的起源和物种形成过程，讨论了这些发现的意义。
