Sillitoe R V, Gopal N, Joyner A L
Developmental Biology Program, Sloan-Kettering Institute, 1275 York Avenue, New York, NY 10021, USA.
Neuroscience. 2009 Sep 1;162(3):574-88. doi: 10.1016/j.neuroscience.2008.12.025. Epub 2008 Dec 24.
The establishment of neural circuits involves both the precise positioning of cells within brain regions and projection of axons to specific target cells. In the cerebellum (Cb), the medial-lateral (M-L) and anterior-posterior (A-P) position of each Purkinje cell (PC) and the topography of its axon can be defined with respect to two coordinate systems within the Cb; one based on the pattern of lobules and the other on PC gene expression in parasagittal clusters in the embryo (e.g. Pcp2) and stripes in the adult (e.g. ZebrinII). The relationship between the embryonic clusters of molecularly defined PCs and particular adult PC stripes is not clear. Using a mouse genetic inducible fate mapping (GIFM) approach and a Pcp2-CreER-IRES-hAP transgene, we marked three bilateral clusters of PC clusters with myristolated green fluorescent protein (mGfp) on approximately embryonic day (E) 15 and followed their fate into adulthood. We found that these three clusters contributed specifically to ZebrinII-expressing PCs, including nine of the adult stripes. This result suggests that embryonic PCs maintain a particular molecular identity, and that each embryonic cluster can contribute PCs to more than one adult M-L stripe. Each PC projects a primary axon to one of the deep cerebellar nuclei (DCN) or the vestibular nuclei in the brainstem in an organized fashion that relates to the position of the PCs along the M-L axis. We characterized when PC axons from the three M-L clusters acquire topographic projections. Using a combination of GIFM to mark the PC clusters with mGfp and staining for human placental alkaline phosphatase (hAP) in Pcp2-CreER-IRES-hAP transgenic embryos we found that axons from each embryonic PC cluster intermingled with neurons within particular DCN or projected out of the Cb toward the vestibular nuclei by E14.5. These studies show that PC molecular patterning, efferent circuitry, and DCN nucleogenesis occur simultaneously, suggesting a link between these processes.
神经回路的建立涉及细胞在脑区中的精确定位以及轴突向特定靶细胞的投射。在小脑（Cb）中，每个浦肯野细胞（PC）的内侧-外侧（M-L）和前后（A-P）位置及其轴突的拓扑结构可以相对于Cb内的两个坐标系来定义；一个基于小叶模式，另一个基于胚胎矢状旁簇（如Pcp2）和成体条纹（如ZebrinII）中的PC基因表达。分子定义的胚胎PC簇与特定成体PC条纹之间的关系尚不清楚。我们使用小鼠基因诱导命运图谱（GIFM）方法和Pcp2-CreER-IRES-hAP转基因，在大约胚胎第15天（E15）用肉豆蔻酰化绿色荧光蛋白（mGfp）标记了三个双侧PC簇，并追踪它们到成年期的命运。我们发现这三个簇专门贡献给表达ZebrinII的PC，包括九个成年条纹。这一结果表明胚胎PC保持特定的分子身份，并且每个胚胎簇可以将PC贡献给不止一个成年M-L条纹。每个PC以一种与PC沿M-L轴的位置相关的有组织方式将一条初级轴突投射到小脑深部核团（DCN）或脑干中的前庭核团之一。我们确定了来自三个M-L簇的PC轴突何时获得拓扑投射。通过结合使用GIFM用mGfp标记PC簇并对Pcp2-CreER-IRES-hAP转基因胚胎中的人胎盘碱性磷酸酶（hAP）进行染色，我们发现到E14.5时，每个胚胎PC簇的轴突与特定DCN内的神经元混合或从小脑向前庭核团投射出小脑。这些研究表明PC分子模式形成、传出回路和DCN核生成同时发生，提示这些过程之间存在联系。
