Department of Anatomy and Neurobiology, Wakayama Medical University, 811-1 Kimiidera, Wakayama City, Wakayama 641-8509, Japan.
Neurosci Lett. 2013 Aug 26;548:73-8. doi: 10.1016/j.neulet.2013.05.024. Epub 2013 May 20.
A member of leucine-rich repeat neuronal protein (Lrrn) family, Lrrn4, is a type I transmembrane protein and functions as a cell adhesion molecule. In our previous report, Lrrn4 is expressed in a subset of small-sized dorsal root ganglion (DRG) neurons of the adult mice. In the present study, we investigated the expression pattern of Lrrn4 in the developing DRGs. The expression of Lrrn4 was first observed in 7% of total DRG neurons at embryonic day (E) 13.5, gradually increasing to 44% at E17.5, reached the maximum level between E17.5 and postnatal day (P) 7, decreased drastically after P7, and became the adult level by P14. Interestingly, the expression of Lrrn4 was mainly observed in TrkC-positive neurons at E13.5, and the predominant expression was shifted from TrkC-positive neurons to TrkA-positive neurons between E15.5 and E17.5. As the central afferents of TrkC-positive and TrkA-positive neurons begin to penetrate into the spinal cord to form synapse with secondary neurons at E13.5 and E15.5, respectively, the time course of Lrrn4 expression may suggest the contribution of Lrrn4 to synaptic formation. In addition, some cell adhesion molecules containing leucine-rich repeat are identified as synaptic adhesion molecules, suggesting that the spatiotemporal expression pattern of Lrrn4 contributes to the development of synaptic function in the DRG neurons.
富含亮氨酸重复神经元蛋白 (LRrn) 家族的一个成员 Lrrn4 是一种 I 型跨膜蛋白，作为细胞黏附分子发挥作用。在我们之前的报告中，Lrrn4 在成年小鼠的一小部分小尺寸背根神经节 (DRG) 神经元中表达。在本研究中，我们研究了 Lrrn4 在发育中的 DRG 中的表达模式。Lrrn4 的表达首先在胚胎期 (E) 13.5 的总 DRG 神经元中观察到 7%，逐渐增加到 E17.5 的 44%，在 E17.5 至出生后第 7 天 (P) 之间达到最大值，P7 后急剧下降，到 P14 时达到成年水平。有趣的是，Lrrn4 的表达在 E13.5 时主要观察到在 TrkC 阳性神经元中，在 E15.5 和 E17.5 之间，主要表达从 TrkC 阳性神经元转移到 TrkA 阳性神经元。由于 TrkC 阳性和 TrkA 阳性神经元的中枢传入纤维分别在 E13.5 和 E15.5 开始穿透脊髓，与二级神经元形成突触，Lrrn4 表达的时间进程可能表明 Lrrn4 对突触形成的贡献。此外，一些含有亮氨酸重复的细胞黏附分子被鉴定为突触黏附分子，这表明 Lrrn4 的时空表达模式有助于 DRG 神经元中突触功能的发育。
