Lalloué Fabrice L, Ayer-Le Lièvre Christiane S
SHU Psychiatrie du Sujet Agé, CH Esquirol, Limoges, France.
Int J Dev Biol. 2005;49(2-3):193-200. doi: 10.1387/ijdb.041933fl.
For the formation of a functional olfactory system, the key processes are neuronal differentiation, including the expression of one or the other olfactory receptors, the correct formation of the nerve and organization of periphero-central connections. These processes take place during embryonic development starting from early stages. Consequently, avian embryos afford an attractive model to study these mechanisms. Taking advantage of species-specific equipment of olfactory receptors genes in different bird species, interspecific avian chimeras were set up by grafting early chick olfactory placodes in same stage quail embryos. Their analysis was performed using different complementary approaches. In situ hybridisation using probes to different chick olfactory receptor (COR) genes indicated that the choice of expression of an olfactory receptor by a neuron is independent of the environment of the olfactory placode and of interactions with the central nervous system. Futhermore, a chick olfactory receptor gene subgroup (COR3 ), absent in the host genome, was expressed by neurons from the graft. The question was then raised of the consequences of such heterospecific differentiation on axonal projections and fiber convergence. The DiI labeling of olfactory fibres in chimeras revealed anomalies in the formation of the nerve from the chick graft. In agreement with the hypothesis of olfactory receptor (OR) involvement in axonal guidance and periphero-central synapse organisation, the presence of migrating cells and axonal fibres from the graft, expressing foreign ORs and having different interactions with the host environment than the host fibres and migrating cells, might explain these anomalies.
对于功能性嗅觉系统的形成而言，关键过程包括神经元分化，其中涉及一种或另一种嗅觉受体的表达、神经的正确形成以及外周与中枢连接的组织。这些过程从胚胎发育早期就开始发生。因此，鸟类胚胎为研究这些机制提供了一个有吸引力的模型。利用不同鸟类物种中嗅觉受体基因的物种特异性特征，通过将早期鸡的嗅觉基板移植到同期鹌鹑胚胎中构建了种间鸟类嵌合体。使用不同的互补方法对它们进行了分析。使用针对不同鸡嗅觉受体（COR）基因的探针进行原位杂交表明，神经元对嗅觉受体表达的选择独立于嗅觉基板的环境以及与中枢神经系统的相互作用。此外，宿主基因组中不存在的一个鸡嗅觉受体基因亚组（COR3）在移植的神经元中表达。于是就产生了这样一个问题：这种异种特异性分化对轴突投射和纤维汇聚有何影响。嵌合体中嗅觉纤维的DiI标记揭示了来自鸡移植体的神经形成存在异常。与嗅觉受体（OR）参与轴突导向和外周与中枢突触组织的假设一致，来自移植体的迁移细胞和轴突纤维表达外来OR，并且与宿主环境的相互作用不同于宿主纤维和迁移细胞，这可能解释了这些异常现象。
