Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California 92093, USA.
J Neurosci. 2012 Oct 10;32(41):14265-70. doi: 10.1523/JNEUROSCI.2693-12.2012.
Fifteen of the 21 innexin (Inx) genes (Hve-inx) found in the genome of the medicinal leech, Hirudo verbana, are expressed in the CNS (Kandarian et al., 2012). Two are expressed pan-neuronally, while the others are restricted in their expression to small numbers of cells, in some cases reflecting the membership of known networks of electrically coupled and dye-coupled neurons or glial cells. We report here that when Hve-inx genes characteristic of discrete coupled networks were expressed ectopically in neurons known not to express them, the experimental cells were found to become dye coupled with the other cells in that network. Hve-inx6 is normally expressed by only three neurons in each ganglion, which form strongly dye-coupled electrical connections with each other [Shortening-Coupling interneuron (S-CI) network] (Muller and Scott, 1981; Dykes and Macagno, 2006). But when Hve-inx6 was ectopically expressed in a variety of central embryonic neurons, those cells became dye coupled with the S-CI network. Similarly, Hve-inx2 is normally uniquely expressed by the ganglion's large glial cells, but when it was ectopically expressed in different central neurons, they became dye coupled to the glial cells. In contrast, overexpression of the pan-neuronal Inx genes Hve-inx1 and Hve-inx14 did not yield any novel instances of dye coupling to pre-existent neuronal networks. These results reveal that expression of certain innexins is sufficient to couple individual neurons to pre-existing networks in the CNS. We propose that a primary determinant of selective neuronal connectivity and circuit formation in the leech is the surface expression of unique subsets of gap junctional proteins.
在医用水蛭 Hirudo verbana 的基因组中发现的 21 个连接蛋白（Inx）基因（Hve-inx）中有 15 个在中枢神经系统（CNS）中表达（Kandarian 等人，2012 年）。其中两个在全神经元中表达，而其他基因则局限于少数细胞中表达，在某些情况下反映了已知的电耦合和染料耦合神经元或神经胶质细胞网络的成员。我们在这里报告，当具有离散耦合网络特征的 Hve-inx 基因在实验细胞中异位表达，而这些实验细胞不表达它们时，发现实验细胞与该网络中的其他细胞发生染料耦合。Hve-inx6 通常仅在每个神经节的三个神经元中表达，这些神经元彼此之间形成强烈的染料耦合电连接[缩短耦合中间神经元（S-CI）网络]（Muller 和 Scott，1981；Dykes 和 Macagno，2006）。但是，当 Hve-inx6 在各种中枢胚胎神经元中异位表达时，这些细胞与 S-CI 网络发生染料耦合。同样，Hve-inx2 通常仅由神经节的大神经胶质细胞表达，但当它在不同的中枢神经元中异位表达时，它们与神经胶质细胞发生染料耦合。相比之下，pan-neuronal Inx 基因 Hve-inx1 和 Hve-inx14 的过表达不会导致与预先存在的神经元网络发生任何新的染料耦合实例。这些结果表明，某些 Innexin 的表达足以将单个神经元与中枢神经系统中预先存在的网络耦合。我们提出，在医用水蛭中，神经元连接和电路形成的选择性的主要决定因素是独特的间隙连接蛋白亚群的表面表达。
