DeLotto Y, Smith C, DeLotto R
Department of Genetics, University of Copenhagen, Denmark.
Mol Gen Genet. 2001 Jan;264(5):643-52. doi: 10.1007/s004380000350.
The spätzle gene is required for proper specification of positional information along the dorsal-ventral axis of the Drosophila embryo and for induction of the innate immune response to fungal infection. It has been shown to encode a precursor of a Nerve Growth Factor-like ligand which is also a member of the cysknot protein superfamily. In dorsal-ventral patterning, the most widely accepted model of the pathway places Spätzle at the end of a ventrally restricted protease cascade that results in the proteolytic processing of the precursor form of Spätzle to an active ligand which is thought to bind to the Toll receptor. Here we show that the spätzle gene encodes at least ten different protein isoforms as a result of complex alternative splicing in precellular blastoderm embryos. Multiple transcripts are clearly present up until the time of cellularization, at which point most transcripts can no longer be detected. Nine isoforms were expressed and at least five are efficiently secreted in a heterologous protein expression system. RNA microinjection experiments demonstrate that three isoforms completely rescue embryos from spätzle null mothers, while most of the others rescue to a lesser extent. The phenotypic rescue activities of several isoforms and the relevance of these isoforms to the generation of the ventralizing signal are discussed.
斯佩兹尔基因对于果蝇胚胎背腹轴上位置信息的正确指定以及对真菌感染的先天免疫反应的诱导是必需的。已表明它编码一种神经生长因子样配体的前体，该配体也是胱氨酸结蛋白超家族的成员。在背腹模式形成中，该信号通路最被广泛接受的模型将斯佩兹尔置于腹侧受限蛋白酶级联反应的末端，该级联反应导致斯佩兹尔前体形式被蛋白水解加工成一种活性配体，据认为该配体与Toll受体结合。在这里我们表明，由于细胞化前胚盘胚胎中复杂的可变剪接，斯佩兹尔基因编码至少十种不同的蛋白质异构体。直到细胞化时，多种转录本都明显存在，此时大多数转录本不再能被检测到。在异源蛋白表达系统中表达了九种异构体，并且至少有五种被有效分泌。RNA显微注射实验表明，三种异构体完全能从斯佩兹尔基因缺失的母体中拯救胚胎，而其他大多数异构体只能在较小程度上拯救胚胎。讨论了几种异构体的表型拯救活性以及这些异构体与腹侧化信号产生的相关性。
