Semaphorins and their receptors in lamprey CNS: Cloning, phylogenetic analysis, and developmental changes during metamorphosis

Abstract

The large, conserved semaphorin gene family encodes axon guidance molecules in both invertebrates and vertebrates. The primitive vertebrate lamprey diverged near the time of vertebrate origins and is useful for understanding the gene duplication events that led to the increased complexity of the vertebrate genome. We characterized the sequence and expression pattern of semaphorins and their receptors genes in the sea lamprey, Petromyzon marinus. We uncovered two members of the semaphorin family in sea lamprey. The first encodes a diffusible class 3 type semaphorin protein that is most similar to the human and mouse Sema3F (71% amino acid identity). The second encodes a transmembrane class 4 type semaphorin that is most similar to mouse Sema4D and human Sema4G, with 38% amino acid identity within the Sema domain. We also identified in lamprey two members of the semaphorin receptor family, lamprey Plexin A1 and Plexin A2. Phylogenetic analysis indicates that lamprey Sema3 and Sema4 represent precursor genes existing prior to the origin of the vertebrate Sema3A-G and Sema4A-G subfamilies. Therefore, the gene duplication event that gave rise to those subfamilies must have occurred after the divergence of jawed vertebrates from jawless fish. These semaphorins and plexins are expressed in unique and dynamic patterns in lamprey spinal cord and brain during development.

Expression of the repulsive guidance molecule RGM and its receptor neogenin after spinal cord injury in sea lamprey

“…Fewer than 50% of severed axons grow into the distal stump within 10–12 weeks post-transection, and most of those grow less than 1 cm beyond the transection site (Lurie and Selzer, 1991, Lurie and Selzer, 1991, Rovainen, 1976, Yin and Selzer, 1983). The presence of chemorepulsive axonal guidance molecules RGM (this article) and Sema3 and Sema4 in lamprey spinal cord (Shifman and Selzer, 2006, Shifman and Selzer, 2007) and the down-regulation of netrin (Shifman and Selzer, 2007), which in some cases can act as a chemoattractant, could contribute to the regenerative failure of some lamprey axons after spinal cord transection however, further experiments will be needed to elucidate RGM role in spinal cord regeneration.…”

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

“…Previously cloned cDNAs for netrin (Shifman and Selzer,2000a) and lamprey Sema3 and Sema4 (Shifman and Selzer,2006) were used as templates for the generation of digoxigenin (DIG)‐labeled sense and antisense riboprobes for in situ hybridization on spinal cord paraffin sections and wholemount preparations of control and spinal‐transected animals.…”

“…Probes were made from the same templates used to make cDNA for sequences and phylogenetics analysis (Shifman and Selzer,2006). The netrin cRNA probe was transcribed from a 221‐bp fragment spanning LamNT (Laminin N‐terminal domain VI) domain of netrin (nucleotides 1–221; GenBank access.…”

“…As a first step in determining the molecular mechanisms involved in guiding and modulating axonal regeneration in the injured spinal cord, we cloned lamprey Sema3, Sema4, and netrin and determined their expression patterns in the spinal cord by in situ hybridization (Shifman and Selzer,2000a,b,2006).…”

Regeneration in the Era of Functional Genomics and Gene Network Analysis

“…Ascending axons also regenerate in the proper direction (Yin and Selzer, 1983; Armstrong et al , 2003). Moreover, injury induces changes in the expression levels of several axon guidance molecules (Shifman and Selzer, 2000a, b, 2006, 2007; Shifman et al , 2009). Some of these guidance molecules, such as UNC5 and neogenin, are differentially expressed between good and bad regenerators, providing proof-of-concept for the identification of differences in gene expression between the two populations.…”