Dynamic expression pattern of Neuronal leucine-rich repeat 4 in mouse sensory neurons during development

在这项研究中，我们检测了NLRR-4在成年和发育中的背根节(DRGs)中的表达。Northern印迹分析表明，NLRR-4mRNA在出生后0天和成体背根神经节均有表达，尤以出生后0天和7天表达最强。原位杂交组织化学显示，NLRR-4mRNA仅在成年小鼠背根神经节的小神经元中表达。同样，在NLRR-4杂合子小鼠中，LacZ染色显示LacZ阳性神经元占总DRG神经元的8%，这一比例与原位杂交组织化学结果相似。在成年小鼠中，约42%的NLRR-4阳性神经元表达受体酪氨酸激酶A(Trk)A，58%的神经元表达Ret。在发育中的背根节中，NLRR-4在胚胎第13.5天开始表达，占DRG神经元总数的7%，以后逐渐增强，在胚胎17.5天达到最大值，达到44%。LacZ阳性神经元占总神经元的百分比在E17.5~P7期间变化不大，在P7后显著降低。作为发育过程中NLRR4表达神经元的特征，NLRR4阳性神经元在胚胎13.5主要表达TrkC。在E17.5和P0之间，NLRR-4阳性神经元主要含有TrkA免疫反应。TrkC阳性神经元比TrkA阳性神经元更早成熟，如轴突向脊髓的支配、突触的形成和突触的成熟。这些结果提示，NLRR-4可能在DRG神经元与脊髓次级神经元接触的突触形成中起作用。

In this study, we examined the expression of NLRR-4 in the adult and developing dorsal root ganglia (DRGs). Northern blotting analysis revealed that the expression of NLRR-4 mRNA was detected between postnatal day (P) 0 and adult DRGs, in particular, the strong expression was observed at P0 and P7. In situ hybridization histochemistry showed that NLRR-4 mRNA was exclusively detected in the small-sized DRG neurons of the adult mice. Likewise, LacZ staining in NLRR-4 heterozygote mice revealed that LacZ-positive neurons were observed in 8% of the total DRG neurons, and this frequency was similar to the results of in situ hybridization histochemistry. Approximately 42% of NLRR-4-positive neurons contained receptor tyrosine kinase (Trk) A immunoreactivity, and 58% expressed Ret immunoreactivity in the adult mice. In the developing DRGs, NLRR-4 expression was first detected in 7% of total DRG neurons at embryonic day (E) 13.5, gradually increased, and reached the maximum level to 44% at E17.5. The percentage of LacZ-positive neurons in total neurons changed little between E17.5 and P7, and drastically reduced after P7. As a results of characterization for NLRR4-expressing neurons during development, NLRR4-positive neurons mainly expressed TrkC at E13.5. Between E17.5 and P0, NLRR-4-positive neurons contained predominantly TrkA-immunoreactivities. TrkC-positive neurons are earlier maturated compared with TrkA-positive neurons such as axonal innervation into the spinal cord, synaptic formation, and synaptic maturation. These results suggested that NLRR-4 might play a role in the synapse formation of DRG neurons contacting to the secondary neurons in the spinal cord.