Kinderman N B, Harrington C A, Drengler S M, Jones K J
Department of Cell Biology, Neurobiology and Anatomy, Loyola University Chicago, Maywood, Illinois 60153, USA.
J Comp Neurol. 1998 Nov 16;401(2):205-16.
A key step in the ability of neurons to survive injury and successfully regenerate involves ribosomal RNA production. Testosterone propionate (TP), augments facial nerve regeneration in the adult hamster. TP modulates the nucleolar reaction in injured facial motoneurons, such that mature ribosome levels increase more rapidly and in greater magnitude than with injury only. In this study, molecular and electron microscopic stereologic approaches were used to determine the effects of axotomy and steroid treatment on ribosomal transcription and processing in facial motoneurons. Castrated adult male hamsters were subjected to right facial nerve transection at the stylomastoid foramen. Half the animals were subcutaneously implanted with one Silastic TP capsule, with the remainder sham implanted. For the in situ hybridization experiments, postoperative survival times were 0.5, 2, or 6 hours. In situ hybridization with a ribosomal DNA probe specific to the external transcribed spacer region located at the 5' end of the ribosomal gene was accomplished. Transcriptional activation of the rRNA gene occurred rapidly, within 2 hours, after injury only. Unexpectedly, TP treatment did not alter the time course or magnitude of rRNA transcriptional activity. For the electron microscope experiments, the postoperative time of 12 hours was selected. Stereologic analysis of 3 nucleolar subcomponents, fibrillar centers (site of rRNA transcription), nucleolonema (site of rRNA processing), and granular material (site of preribosome storage), was accomplished. TP decreased the nucleolonemal strands and the granular material, relative to injury only. These results suggest that, although rRNA transcription is rapidly activated by axotomy, rRNA processing is temporarily stalled. TP does not affect the early, axotomy-induced transcriptional activation of the ribosomal gene, but may, instead, prevent the subsequent disruption in rRNA processing. An hypothesis for the molecular mechanism by which steroids augment the regenerative capabilities of injured facial motoneurons is presented.
神经元在损伤后存活并成功再生的关键步骤涉及核糖体RNA的产生。丙酸睾酮（TP）可促进成年仓鼠面神经的再生。TP调节受损面神经运动神经元的核仁反应，使成熟核糖体水平比仅损伤时增加得更快且幅度更大。在本研究中，采用分子和电子显微镜立体学方法来确定轴突切断术和类固醇治疗对面神经运动神经元核糖体转录和加工的影响。对成年去势雄性仓鼠在茎乳孔处进行右侧面神经横断。一半动物皮下植入一个含TP的硅橡胶胶囊，其余动物进行假植入。对于原位杂交实验，术后存活时间为0.5、2或6小时。使用针对位于核糖体基因5'端的外部转录间隔区的核糖体DNA探针进行原位杂交。仅在损伤后2小时内，rRNA基因的转录激活迅速发生。出乎意料的是，TP治疗并未改变rRNA转录活性的时间进程或幅度。对于电子显微镜实验，选择术后12小时的时间点。对3个核仁亚组分，即纤维中心（rRNA转录位点）、核仁丝（rRNA加工位点）和颗粒物质（前核糖体储存位点）进行立体学分析。与仅损伤相比，TP减少了核仁丝和颗粒物质。这些结果表明，虽然轴突切断术可迅速激活rRNA转录，但rRNA加工暂时停滞。TP不影响轴突切断术诱导的核糖体基因早期转录激活，但可能反而防止随后rRNA加工的中断。本文提出了类固醇增强受损面神经运动神经元再生能力的分子机制假说。
