Following up my recent overview of axon guidance, Cell recently offered an interesting study into the control of axon guidance (López-Bendito et al.), accompanied by an expert commentary by Hanashima et al. Now, I’m not so up on my neuroanatomy, so I focused on their more general summaries. In “Building Bridges to the Cortex,” Hanashima et al. describe:
In this issue of Cell, López-Bendito and colleagues propose a new mechanism of navigation for thalamocortical axons in which tangentially migrating cells within the ventral telencephalon guide thalamic axons towards their final destination in the neocortex. These migrating cells, referred to as “corridor cells,” appear to create a permissive bridge between the diencephalic/telencephalic boundary and the pallial/subpallial boundary, completeing the relay between the intermediate targets of the thalamocortical pathway (Figure 1).
So what is it about these corridor cells that thalamocortical axons find so appealing? Interestingly, López-Bendito et al. (2006) find that the navigation of thalamocortical axons utilizes the same mechanism previously identified as crucial for guiding interneuron migration from the MGE to the cortex (Flames et al., 2004). In their previous work, this group showed that isoforms of Neuregulin-1 (Nrg1), membrane bound Nrg1 (CRD-Nrg1) and secreted Nrg1 (Ig-Nrg1), as as short-range and long-range attractants for cortical interneurons, respectively. Now it appears that the same receptor/ligand combination is utilized in the guidance of thalamocrotical axons…
And their conclusion:
… the discovery of bridging cells is a significant step toward understanding the early process of thalamocortical navigation to the cortex. Whatever their further roles might be, their bridging function in shepherding thalamocortical axons toward the cortex suggests that guideposts play a more dynamic function in pathfinding than simply providing cues for turning.
It’s this last bit that contrasts starkly with my previous post on Maskery & Shinbrot’s review. Are these corridor cells the stochastic factors that Maskery & Shinbrot describe, which previously gave the impression of insensitivity to turning cues, or are corridor cells a special situation?
- Building bridges to the cortex. Hanashima C, Molnar Z, Fishell G. Cell. 2006 Apr 7; 125(1):24-7. Pubmed.
- Tangential neuronal migration controls axon guidance: a role for neuregulin-1 in thalamocortical axon navigation. Lopez-Bendito G, Cautinat A, Sanchez JA, Bielle F, Flames N, Garratt AN, Talmage DA, Role LW, Charnay P, Marin O, Garel S. Cell. 2006 Apr 7; 125(1):127-42. Pubmed.
- Deterministic and stochastic elements of axonal guidance. Maskery S, Shinbrot T. Annu Rev Biomed Eng. 2005; 7:187-221. Pubmed.