Laumonnerie Christophe, Bechara Ahmad, Vilain Nathalie, Kurihara Yukiko, Kurihara Hiroki, Rijli Filippo M
Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, Basel 4058, Switzerland.
Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8654, Japan Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), Chiyoda-ku, Tokyo, 102-0075, Japan.
Development. 2015 Nov 1;142(21):3704-12. doi: 10.1242/dev.128736. Epub 2015 Sep 28.
Facial somatosensory input is relayed by trigeminal ganglion (TG) neurons and serially wired to brainstem, thalamus and cortex. Spatially ordered sets of target neurons generate central topographic maps reproducing the spatial arrangement of peripheral facial receptors. Facial pattern provides a necessary template for map formation, but may be insufficient to impose a brain somatotopic pattern. In mice, lower jaw sensory information is relayed by the trigeminal nerve mandibular branch, whose axons target the brainstem dorsal principal sensory trigeminal nucleus (dPrV). Input from mystacial whiskers is relayed by the maxillary branch and forms a topographic representation of rows and whiskers in the ventral PrV (vPrV). To investigate peripheral organisation in imposing a brain topographic pattern, we analysed Edn1(-/-) mice, which present ectopic whisker rows on the lower jaw. We found that these whiskers were innervated by mandibular TG neurons which initially targeted dPrV. Unlike maxillary TG neurons, the ectopic whisker-innervating mandibular neuron cell bodies and pre-target central axons did not segregate into a row-specific pattern nor target the dPrV with a topographic pattern. Following periphery-driven molecular repatterning to a maxillary-like identity, mandibular neurons partially redirected their central projections from dPrV to vPrV. Thus, while able to induce maxillary-like molecular features resulting in vPrV final targeting, a spatially ordered lower jaw ectopic whisker pattern is insufficient to impose row-specific pre-target organisation of the central mandibular tract or a whisker-related matching pattern of afferents in dPrV. These results provide novel insights into periphery-dependent versus periphery-independent mechanisms of trigeminal ganglion and brainstem patterning in matching whisker topography.
面部躯体感觉输入由三叉神经节（TG）神经元中继，并依次连接到脑干、丘脑和皮层。按空间顺序排列的靶神经元集合生成中央地形图，再现外周面部感受器的空间排列。面部模式为图谱形成提供了必要的模板，但可能不足以强加脑躯体定位模式。在小鼠中，下颌感觉信息由三叉神经下颌支中继，其轴突靶向脑干背侧主要感觉三叉神经核（dPrV）。触须的输入由上颌支中继，并在腹侧PrV（vPrV）中形成触须排和触须的地形图。为了研究外周组织在强加脑地形图模式中的作用，我们分析了Edn1（-/-）小鼠，这些小鼠在下颌上出现异位触须排。我们发现这些触须由最初靶向dPrV的下颌TG神经元支配。与上颌TG神经元不同，支配异位触须的下颌神经元细胞体和靶前中央轴突没有分离成排特异性模式，也没有以地形图模式靶向dPrV。在由外周驱动的分子重编程为类似上颌的特性后，下颌神经元将其中央投射部分地从dPrV重新定向到vPrV。因此，虽然能够诱导类似上颌的分子特征从而导致最终靶向vPrV，但空间有序的下颌异位触须模式不足以强加中央下颌束的排特异性靶前组织或dPrV中传入神经的触须相关匹配模式。这些结果为三叉神经节和脑干在匹配触须地形图中的外周依赖性与外周独立性机制提供了新的见解。
