Differential expression of Class 3 and 4 semaphorins and netrin in the lamprey spinal cord during regeneration

Abstract

To explore the role of axon guidance molecules during regeneration in the lamprey spinal cord, we examined the expression of mRNAs for semaphorin 3 (Sema3), semaphorin 4 (Sema4), and netrin during regeneration by in situ hybridization. Control lampreys contained netrin-expressing neurons along the length of the spinal cord. After spinal transection, netrin expression was downregulated in neurons close (500 mum to 10 mm) to the transection at 2 and 4 weeks. A high level of Sema4 expression was found in the neurons of the gray matter and occasionally in the dorsal and the edge cells. Fourteen days after spinal cord transection Sema4 mRNA expression was absent from dorsal and edge cells but was still present in neurons of the gray matter. At 30 days the expression had declined to some extent in neurons and was absent in dorsal and edge cells. In control animals, Sema3 was expressed in neurons of the gray matter and in dorsal and edge cells. Two weeks after transection, Sema3 expression was upregulated near the lesion, but absent in dorsal cells. By 4 weeks a few neurons expressed Sema3 at 20 mm caudal to the transection but no expression was detected 1 mm from the transection. Isolectin I-B(4) labeling for microglia/macrophages showed that the number of Sema3-expressing microglia/macrophages increased dramatically at the injury site over time. The downregulation of netrin and upregulation of Sema3 near the transection suggests a possible role of netrin and semaphorins in restricting axonal regeneration in the injured spinal cord.

A Preliminary Genetic Map in <b><i>Solea senegalensis</i></b> (Pleuronectiformes, Soleidae) Using BAC-FISH and Next-Generation Sequencing

“…Some semaphorins and their receptors regulate immune cell activation or differentiation; whereas others navigate the trafficking of immune cells [Ito et al, 2012]. In lampreys, semaphorins 3 and 4 are involved in guiding and modulating axonal regeneration in injured spinal cord [Shifman and Selzer, 2007]. Semaphorin 7A is identified as a neural guidance protein; it is reported to intensify inflammatory damage by promoting neutrophil trafficking and is strongly induced by hypoxia challenge in a process regulated by the hypoxia-inducible factor (HIF-1) [Morote-Garcia et al, 2012].…”

Molecular/genetic manipulation of extrinsic axon guidance factors for CNS repair and regeneration

“…Such changes in expression often correlate with a lack of regeneration. For example, comparison of mRNA levels by in situ hybridization between the intact and transected adult lamprey spinal cord revealed a down-regulation of netrin and up-regulation of semaphorin near the transection site (Shifman and Selzer 2007), possibly accounting for regenerative failure of approximately 50% of the transected spinal axons. Semaphorin 3A was also recently shown to be expressed in terminal Schwann cells preferentially associated with fast-fatigable muscle fibers following injury.…”

Semaphorin and neuropilin expression during early morphogenesis of Xenopus laevis

“…Therefore, detailed knowledge of the expression pattern of semaphorins and their cognate receptors is key to understanding their in vivo function. Since semaphorins were discovered as axon guidance molecules, their expression has primarily been studied in the nervous system (Luo et al, 1995;Melendez-Herrera and Varela-Echavarria, 2006;Pasterkamp et al, 2007;Shifman and Selzer, 2007). However, expression in early embryonic morphogenesis has not been systematically addressed.…”