Dunipace L, Meister S, McNealy C, Amrein H
Department of Genetics, Duke University Medical Center, 252 CARL Building, Research Drive, Box 3054, Durham, NC 27710, USA.
Curr Biol. 2001 Jun 5;11(11):822-35. doi: 10.1016/s0960-9822(01)00258-5.
Taste is an important sensory modality in most animals. In Drosophila, taste is perceived by gustatory neurons located in sensilla distributed on several different appendages throughout the body of the animal. Here we show that the gustatory receptors are encoded by a family of at least 54 genes (Gr genes), most of which are expressed exclusively in a small subset of taste sensilla located in narrowly defined regions of the fly's body.
BLAST searches with the predicted amino acid sequences of 6 7-transmembrane-receptor genes of unknown function and 20 previously identified, putative gustatory receptor genes led to the identification of a large gene family comprising at least 54 genes. We investigated the expression of eight genes by using a Gal4 reporter gene assay and found that five of them were expressed in the gustatory system of the fly. Four genes were expressed in 1%-4% of taste sensilla, located in well-defined regions of the proboscis, the legs, or both. The fifth gene was expressed in about 20% of taste sensilla in all major gustatory organs, including the taste bristles on the anterior wing margin. Axon-tracing experiments demonstrated that neurons expressing a given Gr gene project their axons to a spatially restricted domain of the subesophageal ganglion in the fly brain.
Our findings suggest that each taste sensillum represents a discrete, functional unit expressing at least one Gr receptor and that most Gr genes are expressed in spatially restricted domains of the gustatory system. These observations imply the potential for high taste discrimination of the Drosophila brain.
味觉是大多数动物重要的感觉方式。在果蝇中，味觉由位于分布于动物全身多个不同附肢上的感觉器中的味觉神经元感知。在此我们表明，味觉受体由一个至少包含54个基因（Gr基因）的家族编码，其中大多数基因仅在位于果蝇身体狭窄定义区域的一小部分味觉感觉器中表达。
对6个功能未知的7跨膜受体基因和20个先前鉴定的假定味觉受体基因的预测氨基酸序列进行BLAST搜索，导致鉴定出一个至少包含54个基因的大基因家族。我们通过使用Gal4报告基因检测法研究了8个基因的表达，发现其中5个基因在果蝇的味觉系统中表达。4个基因在位于喙、腿或两者明确区域的1% - 4%的味觉感觉器中表达。第五个基因在所有主要味觉器官中约20%的味觉感觉器中表达，包括前翅边缘的味觉刚毛。轴突追踪实验表明，表达特定Gr基因的神经元将其轴突投射到果蝇大脑中咽下神经节的空间受限区域。
我们的研究结果表明，每个味觉感觉器代表一个表达至少一种Gr受体的离散功能单元，并且大多数Gr基因在味觉系统的空间受限区域中表达。这些观察结果暗示果蝇大脑具有高度味觉辨别能力的潜力。
