Fan G, Katz D M
Department of Neurosciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106.
Development. 1993 May;118(1):83-93. doi: 10.1242/dev.118.1.83.
Although some sensory ganglion cells in mature animals are catecholaminergic, most mammalian sensory neurons that express the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH) do so only transiently during early gangliogenesis in vivo. The lack of TH expression at later stages appears to be due to modulation of this catecholaminergic potential. A previous study showed that the phenotype reappears, for example, when E16.5 and older sensory ganglia are dissociated in culture into single cells, suggesting that extracellular influences can modulate TH expression. Moreover, TH expression in dissociate cultures is cell-density dependent, as a four-fold increase in plating density led to a 30% decrease in the percentage of TH neurons. The present study demonstrates that inhibition of TH expression in high density cultures is mediated by ganglionic non-neuronal cells (NNC), as removal of NNC abolished density-dependent inhibition. Moreover, plating E16.5 trigeminal neurons at low density on top of NNC monolayers resulted in an 85% decrease in the percentage of TH neurons. Treatment of cultures with non-neuronal cell conditioned medium (NNC-CM) reproduced the effect of coculture with NNC, suggesting that diffusible factors from NNC were involved in the inhibition of TH. The inhibitory effect of NNC-CM was mimicked by treatment of dissociate cultures with ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF). However, immunoprecipitation of NNC-CM with antibodies against LIF or CNTF showed that only anti-LIF antibodies were able partially to remove the TH inhibitory activity of NNC-CM. Therefore, LIF is one, but not the only, factor mediating NNC inhibition of TH expression in cultured sensory neurons. In summary, these data indicate that ganglionic NNC can regulate sensory transmitter phenotype in culture by inhibiting expression of specific molecular traits. The finding that LIF can partially account for the inhibitory effect of ganglionic NNC on TH expression suggests a novel role for this cytokine in regulating differentiation of catecholaminergic properties in sensory neurons.
虽然成熟动物中的一些感觉神经节细胞是儿茶酚胺能的，但大多数表达儿茶酚胺合成酶酪氨酸羟化酶（TH）的哺乳动物感觉神经元在体内神经节发生早期只是短暂表达。后期缺乏TH表达似乎是由于这种儿茶酚胺能潜能受到了调节。先前的一项研究表明，例如，当E16.5及更成熟的感觉神经节在培养中解离成单个细胞时，该表型会再次出现，这表明细胞外影响可以调节TH表达。此外，解离培养物中TH的表达依赖于细胞密度，因为接种密度增加四倍会导致TH神经元百分比降低30%。本研究表明，高密度培养物中TH表达的抑制是由神经节非神经元细胞（NNC）介导的，因为去除NNC消除了密度依赖性抑制。此外，将E16.5三叉神经元低密度接种在NNC单层上，导致TH神经元百分比降低85%。用非神经元细胞条件培养基（NNC-CM）处理培养物重现了与NNC共培养的效果，表明NNC的可扩散因子参与了对TH的抑制。用睫状神经营养因子（CNTF）和白血病抑制因子（LIF）处理解离培养物可模拟NNC-CM的抑制作用。然而，用抗LIF或CNTF抗体对NNC-CM进行免疫沉淀表明，只有抗LIF抗体能够部分去除NNC-CM的TH抑制活性。因此，LIF是介导培养的感觉神经元中NNC对TH表达抑制的一个因素，但不是唯一因素。总之，这些数据表明神经节NNC可以通过抑制特定分子特征的表达来调节培养中的感觉递质表型。LIF可以部分解释神经节NNC对TH表达的抑制作用，这一发现表明这种细胞因子在调节感觉神经元中儿茶酚胺能特性的分化方面具有新的作用。
