Transcription profiling of trigeminal ganglia of Brn3a knockout and wild type mice to determine the regulatory targets of transcription factor Brn3a

Mice lacking the POU-domain transcription factor Brn3a exhibit marked defects in sensory axon growth and abnormal sensory apoptosis. We have determined the regulatory targets of Brn3a in the developing trigeminal ganglion using microarray analysis of Brn3a mutant mice. These results show that Brn3 mediates the coordinated expression of neurotransmitter systems, ion channels, structural components of axons and inter- and intracellular signaling systems. Loss of Brn3a also results in the ectopic expression of transcription factors normally detected in earlier developmental stages and in other areas of the nervous system. Target gene expression is normal in heterozygous mice, consistent with prior work showing that autoregulation by Brn3a results in gene dosage compensation. Detailed examination of the expression of several of these downstream genes reveals that the regulatory role of Brn3a in the trigeminal ganglion appears to be conserved in more posterior sensory ganglia but not in the CNS neurons that express this factor. Experiment Overall Design: Microarrays used to compare the patterns of gene expression in the trigeminal ganglia of Brn3a knockout and wild-type mice. Embryonic day 13.5 (E13.5) was chosen because at this point in development mutant mice exhibit major defects in sensory axon growth, but have yet to undergo the period of extensive sensory neuron death associated with later stages.缺失POU结构域转录因子（POU-domain transcription factor）Brn3a的小鼠，会表现出显著的感觉轴突生长缺陷与异常的感觉细胞凋亡。本研究通过对Brn3a突变小鼠进行微阵列（microarray）分析，明确了发育中三叉神经节内Brn3a的调控靶标。上述结果表明，Brn3a可介导神经递质系统、离子通道、轴突结构组分以及细胞间与细胞内信号系统的协同表达。Brn3a缺失还会导致正常仅在发育早期阶段以及神经系统其他区域中表达的转录因子出现异位表达。杂合子小鼠的靶基因表达水平正常，这与此前研究结果一致——此前研究显示Brn3a的自调控可产生基因剂量补偿效应。对部分此类下游基因的表达模式进行详细分析后发现，Brn3a在三叉神经节中的调控功能，在更靠后的感觉神经节中似乎具有保守性，但在表达该因子的中枢神经系统（Central Nervous System，CNS）神经元中则不具备这一保守性。实验整体设计：采用微阵列（microarray）比较Brn3a敲除型与野生型小鼠三叉神经节内的基因表达模式。选择胚胎第13.5天（E13.5）作为研究节点，是因为在此发育阶段，突变小鼠已出现明显的感觉轴突生长缺陷，但尚未进入与发育后期相关的大规模感觉神经元死亡阶段。