Clonally related, Notch-differentiated spinal neurons integrate into distinct circuits.
Clonally related, Notch-differentiated spinal neurons integrate into distinct circuits.
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DOI：
10.7554/elife.83680
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发表时间：
2022-12-29
期刊：
影响因子：
7.7
通讯作者：
Bagnall MW
中科院分区：
文献类型：
--
作者：
Bello-Rojas S;Bagnall MW
共享谱系对神经元连接模式有不同的影响。在哺乳动物的皮层中，兴奋性的姐妹神经元组装成共享的微电路。相反，在果蝇中，具有不同Notch表达水平的姐妹神经元（NotchON/NotchOFF）发展出不同的身份，并分化成不同的回路。在脊椎动物的脊髓和小脑中已经观察到Notch分化的姐妹神经元，但它们是否整合到共享或不同的回路中仍然未知。在这里，我们评估如何在斑马鱼的姐妹V2 a（NotchOFF）/V2 b（NotchON）神经元整合到脊髓回路。使用体内标记的方法，我们确定了对姐妹V2 a/B神经元出生的个别Vsx 1+祖细胞，并观察到它们有胞体在彼此接近和相似的轴突轨迹。然而，配对的全细胞电生理学和光遗传学揭示，姐妹V2 a/B神经元从不同的突触前来源接收输入，彼此不通信，并且连接到很大程度上不同的目标。这些结果类似于果蝇的发散连接，并代表了第一个证据Notch分化电路整合在脊椎动物系统。大脑由神经元组成，这些神经元是在胚胎发育过程中从称为祖细胞的细胞中产生的。来自同一祖细胞的神经元被认为是“姐妹”。在小鼠的某些大脑区域，姐妹神经元通常连接到共享网络中，这意味着它们更有可能从相同的神经元接收输入，并比非姐妹细胞彼此连接。相比之下，在无脊椎动物中，如果蝇，姐妹神经元通常具有不同的身份，并且不太可能相互连接。这可能是因为果蝇中的姐妹神经元通常具有不同水平的Notch蛋白质，该蛋白质在确定细胞身份方面起着重要作用。脊椎动物和无脊椎动物在许多方面都是不同的，目前还不清楚Notch水平是否决定了脊椎动物中哪些姐妹神经元像果蝇一样连接在一起。为了进行研究，Bello-Rojas和Bagnall研究了斑马鱼胚胎脊髓中的两个神经元，它们来自相同类型的祖细胞：具有低水平Notch的V2 a神经元和具有高水平Notch的V2 b神经元。与人类一样，鱼类也是脊椎动物;然而，它们的胚胎大多是透明的，这使得使用显微镜更容易跟踪它们的神经元在发育过程中如何进行连接。这使得Bello-Rojas和Bagnall能够监测V2 a和V2 b姐妹神经元是否加入了相同的网络，就像其他脊椎动物一样，或者不同的网络，类似于果蝇中的姐妹神经元，它们也具有不同的Notch水平。Bello-Rojas和Bagnall发现姐妹V2 a和V2 b神经元彼此靠近，似乎通过类似的路径连接。然而，更深入的研究表明，姐妹神经元并没有从同一来源接收输入。它们也没有相互连接或相同的输出神经元，这表明V2 a和V2 b姐妹神经元是不同网络的一部分。这是Notch水平首次被证明可以调节脊椎动物物种中神经元将加入的网络。由于V2 a和V2 b神经元参与控制身体运动，未来的工作应该确定将产生这些神经元的祖细胞添加到脊髓中是否可以帮助神经元网络在受伤或疾病后恢复。
Shared lineage has diverse effects on patterns of neuronal connectivity. In mammalian cortex, excitatory sister neurons assemble into shared microcircuits. In Drosophila, in contrast, sister neurons with different levels of Notch expression (NotchON/NotchOFF) develop distinct identities and diverge into separate circuits. Notch-differentiated sister neurons have been observed in vertebrate spinal cord and cerebellum, but whether they integrate into shared or distinct circuits remains unknown. Here, we evaluate how sister V2a (NotchOFF)/V2b (NotchON) neurons in the zebrafish integrate into spinal circuits. Using an in vivo labeling approach, we identified pairs of sister V2a/b neurons born from individual Vsx1+ progenitors and observed that they have somata in close proximity to each other and similar axonal trajectories. However, paired whole-cell electrophysiology and optogenetics revealed that sister V2a/b neurons receive input from distinct presynaptic sources, do not communicate with each other, and connect to largely distinct targets. These results resemble the divergent connectivity in Drosophila and represent the first evidence of Notch-differentiated circuit integration in a vertebrate system. The brain is populated by neurons which are generated during embryonic development from cells called progenitors. Neurons that come from the same progenitor cell are considered to be ‘sisters’. In certain brain regions of mice, sister neurons are often wired into shared networks, meaning they are more likely to receive input from the same neurons and connect with each other than non-sister cells. In contrast, in invertebrate animals, like the fruit fly, sister neurons often have different identities and are less likely to connect with each other. This may be because sister neurons in fruit flies often have varied levels of a protein called Notch, which plays an important role in establishing the identity of cells. Vertebrate and invertebrate animals are different in many respects, and it remained unclear whether Notch levels dictate which sister neurons connect together in vertebrates as they do in fruit flies. To investigate, Bello-Rojas and Bagnall studied two neurons in the spinal cord of zebrafish embryos which come from the same type of progenitor cell: the V2a neuron which has low levels of Notch, and the V2b neuron which has high levels of Notch. Fish, like humans, are vertebrates; however, their embryos are mostly transparent, making it easier to track how their neurons make connections during development using a microscope. This enabled Bello-Rojas and Bagnall to monitor whether V2a and V2b sister neurons joined the same network, like in other vertebrates, or different networks, akin to sister neurons in fruit flies which also have differing levels of Notch. Bello-Rojas and Bagnall found that sister V2a and V2b neurons stayed close to one another and seemed to connect through similar paths. However, closer investigation revealed that the sister neurons did not receive input from the same source. They also did not connect to each other or the same output neuron, suggesting that V2a and V2b sister neurons are part of different networks. This is the first time Notch levels have been shown to regulate which network a neuron will join in a vertebrate species. Since the V2a and V2b neurons are involved in controlling body movement, future work should determine whether adding progenitor cells that produce these neurons into the spinal cord could help the neuron network recover after injury or disease.