The term Cajal–Retzius cell is applied to neurons of the human embryonic marginal zone which display, as a salient feature, radial ascending processes that contact the pial surface, and a horizontal axon plexus located in the deep marginal zone. These cells were first described by Retzius (Retzius, 1893, 1894). Cajal-Retzius cells possess very long (1000- to 2000-m) horizontal axons that form asymmetric synaptic contacts with dendritic shafts or spines of neocortical pyramidal cells. Although their exact origin remains a subject of controversy, the caudomedial wall of the telencephalic vesicle has been proposed as the primary source.

History

Cajal described in 1891 slender horizontal bipolar cells in the developing marginal zone of lagomorphs.(See the Cajal's original drawing of the cells) These cells were considered by Retzius as homologues to the cells he found in humans and in other mammals (Retzius, 1893, 1894). Similar cells are also present in the rodent marginal zone, and are usually termed ‘Cajal–Retzius cells'.

Role in the cortex

CR cells establish early neuronal circuitry in the developing brain (Aguiló et al., 1999), and express a number of genes known to be important in human cerebral development:

• LIS1 (Clark et al., 1997), which is mutated in lissencephaly;
• EMX2 (Mallamaci et al., 1998);
• Fukutin (Saito et al., 2000);
• RELN (Meyer and Goffinet, 1998). The gene RELN encodes the protein reelin, which is secreted extracellularly by layer I neurones through a constitutive, nonvesicular mechanism (Lacor et al., 2000). This extracellular matrix protein, which is also secreted by Cajal-Retzius neurons, serves as a signal to dissociate for migrating neurons, which travel in clusters, and controls the formation of cortical layers. Lack of reelin, as in the reeler mouse mutant, disturbance of the reelin signaling pathway or ablation of Cajal-Retzius cells causes disorders in cortical lamination.

Sources

• Retzius G (1893) Die Cajal'schen Zellen der Grosshirnrinde beim Menschen und bei Säugetieren. Biologische Untersuchungen, Neue Folge 5:1–8.

• Retzius G (1894) Weitere Beiträge zur Kenntniss der Cajal'schen Zellen der Grosshirnrinde des Menschen. Biologische Untersuchungen. Neue Folge 6:29–36.

• Meyer G, Goffinet AM, Fairen A. (1999) What is a Cajal-Retzius cell? A reassessment of a classical cell type based on recent observations in the developing neocortex. Cereb Cortex. 9(8):765-75. PMID 10600995

References

Links

• Feature Article: What is a Cajal–Retzius cell? A Reassessment of a Classical Cell Type Based on Recent Observations in the Developing Neocortex - Cerebral Cortex, Vol. 9, No. 8, 765-775, December 1999

• Active Networks in the Early Brain - "Editors' Choice: Highlights of the recent literature" in the journal Science, 13 September 2002, Vol. 297. no. 5588, p. 1773

CNS neurons | Eponymous anatomical structures | Клетка Кахаля — Ретциуса