National Centre for Biological Sciences, TIFR, UAS-GKVK Campus, Bangalore 560065, India.
Dev Biol. 2013 Jan 15;373(2):322-37. doi: 10.1016/j.ydbio.2012.11.003. Epub 2012 Nov 10.
The complete neuronal repertoire of the central brain of Drosophila originates from only approximately 100 pairs of neural stem cells, or neuroblasts. Each neuroblast produces a highly stereotyped lineage of neurons which innervate specific compartments of the brain. Neuroblasts undergo two rounds of mitotic activity: embryonic divisions produce lineages of primary neurons that build the larval nervous system; after a brief quiescence, the neuroblasts go through a second round of divisions in larval stage to produce secondary neurons which are integrated into the adult nervous system. Here we investigate the lineages that are associated with the larval antennal lobe, one of the most widely studied neuronal systems in fly. We find that the same five neuroblasts responsible for the adult antennal lobe also produce the antennal lobe of the larval brain. However, there are notable differences in the composition of larval (primary) lineages and their adult (secondary) counterparts. Significantly, in the adult, two lineages (lNB/BAlc and adNB/BAmv3) produce uniglomerular projection neurons connecting the antennal lobe with the mushroom body and lateral horn; another lineage, vNB/BAla1, generates multiglomerular neurons reaching the lateral horn directly. lNB/BAlc, as well as a fourth lineage, vlNB/BAla2, generate a diversity of local interneurons. We describe a fifth, previously unknown lineage, BAlp4, which connects the posterior part of the antennal lobe and the neighboring tritocerebrum (gustatory center) with a higher brain center located adjacent to the mushroom body. In the larva, only one of these lineages, adNB/BAmv3, generates all uniglomerular projection neurons. Also as in the adult, lNB/BAlc and vlNB/BAla2 produce local interneurons which, in terms of diversity in architecture and transmitter expression, resemble their adult counterparts. In addition, lineages lNB/BAlc and vNB/BAla1, as well as the newly described BAlp4, form numerous types of projection neurons which along the same major axon pathways (antennal tracts) used by the antennal projection neurons, but which form connections that include regions outside the "classical" olfactory circuit triad antennal lobe-mushroom body-lateral horn. Our work will benefit functional studies of the larval olfactory circuit, and shed light on the relationship between larval and adult neurons.
果蝇中枢神经系统的完整神经元库仅起源于大约 100 对神经干细胞，即神经母细胞。每个神经母细胞产生一个高度定型的神经元谱系，这些神经元支配大脑的特定区域。神经母细胞经历两轮有丝分裂活动：胚胎分裂产生构建幼虫神经系统的初级神经元谱系；短暂静止后，神经母细胞在幼虫期进行第二轮分裂，产生整合到成虫神经系统中的次级神经元。在这里，我们研究了与幼虫触角叶相关的谱系，触角叶是果蝇中研究最广泛的神经元系统之一。我们发现，负责成虫触角叶的五个相同神经母细胞也产生幼虫大脑的触角叶。然而，幼虫（初级）谱系及其成虫（次级）对应物的组成存在显著差异。值得注意的是，在成虫中，两个谱系（lNB/BAlc 和 adNB/BAmv3）产生单神经节投射神经元，将触角叶与蘑菇体和侧角连接起来；另一个谱系 vNB/BAla1 则产生直接到达侧角的多神经节神经元。lNB/BAlc 以及第四个谱系 vlNB/BAla2 产生多种局部中间神经元。我们描述了第五个以前未知的谱系 BAlp4，它将触角叶的后部分和相邻的三脑（味觉中心）与位于蘑菇体旁边的高级脑中心连接起来。在幼虫中，只有其中一个谱系 adNB/BAmv3 产生所有的单神经节投射神经元。与成虫一样，lNB/BAlc 和 vlNB/BAla2 产生的局部中间神经元在结构和递质表达的多样性方面与成虫对应物相似。此外，谱系 lNB/BAlc 和 vNB/BAla1 以及新描述的 BAlp4 形成了许多类型的投射神经元，这些神经元沿着与触角投射神经元相同的主要轴突途径（触角束），但形成的连接包括“经典”嗅觉回路三联体触角叶-蘑菇体-侧角之外的区域。我们的工作将有益于幼虫嗅觉回路的功能研究，并阐明幼虫和成虫神经元之间的关系。
