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

在这项研究中，我们研究了NLRR-4在成人和发育中的背根神经节（DRG）的表达。北方印迹分析显示，NLRR-4 mRNA在出生后0天（P）至成年后的背根节中均有表达，尤其是在P0和P7时表达较强。原位杂交组织化学结果显示，NLRR-4 mRNA仅在成年小鼠背根神经节的小型神经元中表达。同样，在NLRR-4杂合子小鼠的LacZ染色显示，LacZ阳性神经元中观察到的总DRG神经元的8%，这个频率是类似的原位杂交组织化学的结果。大约42%的NLRR-4阳性神经元含有受体酪氨酸激酶（Trk）A免疫反应性，58%表达Ret免疫反应性的成年小鼠。在发育中的DRG中，NLRR-4在胚胎（E）13.5天首先在总DRG神经元的7%中检测到表达，然后逐渐增加，并在E17.5达到最大水平至44%。LacZ阳性神经元占总神经元的百分比在E17.5和P7之间变化不大，并且在P7之后急剧减少。作为发育期间NLRR 4表达神经元的表征结果，NLRR 4阳性神经元主要在E13.5表达TrkC。在E17.5和P0之间，NLRR-4阳性神经元主要含有TrkA免疫反应性。与TrkA阳性神经元相比，TrkC阳性神经元更早成熟，例如轴突神经支配进入脊髓、突触形成和突触成熟。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.