Cajal–Retzius cell

Cajal–Retzius cells (CR cells) (also known as Horizontal cells of Cajal) are a heterogeneous population of morphologically and molecularly distinct reelin-producing cell types in the marginal zone/layer I of the developmental cerebral cortex and in the immature hippocampus of different species and at different times during embryogenesis and postnatal life. Cajal–Retzius cells (CR cells) (also known as Horizontal cells of Cajal) are a heterogeneous population of morphologically and molecularly distinct reelin-producing cell types in the marginal zone/layer I of the developmental cerebral cortex and in the immature hippocampus of different species and at different times during embryogenesis and postnatal life. These cells were discovered by two scientists, Santiago Ramón y Cajal and Gustaf Retzius, at two different times and in different species. They are originated in the developing brain in multiple sites within the neocortex and hippocampus. From there, Cajal–Retzius (CR) cells experience migration through the marginal zone, originating the layer I of the cortex. As these cells are involved in the correct organization of the developing brain, there are several studies implicating CR cells in neurodevelopmental disorders, especially schizophrenia, bipolar disorder, autism, lissencephaly and temporal lobe epilepsy. In 1971 it was described that it was very difficult to find a CR cell in the adult cortex, because of the constant number of these cells and the fact that as the brain grows, the distance between these cells increases, required the observation of a great number of preparations to find one of these cells.In mice, CR cells are generated very early in the development, appearing between 10,5 and 12,5 embryonic days. Cajal–Retzius cells were described to migrate tangentially in the marginal zone, a superficial layer of the preplate in the cortical neuroepithelium, According to some studies, this migration depends on the site where the cell was generated, showing a link between the origin, the migration and the destination of the cell. Studies have shown that Cajal–Retzius cells have different origins, both in the neocortex and in the hippocampus. In the neocortex they originate in the local pallium ventricular zone, the pallial-subpallial border of the ventral pallium, a region at the septum, the cortical hem and the retrobulbar ventricular zone. In 2006 it was demonstrated that in mouse cells, the meninges control the migration of the CR cells in the cortical hem. Subpopulations of these neurons from the septum and pallial-subpallial border express the homeodomain transcription factor Dbx1 and migrate to the medial, dorsolateral and piriform cortex and though genetically different from the other subpopulations (Dbx1 negative), all have the same morphological and electrophysiological properties, despite the different origins of CR cells. Cajal–Retzius cells are involved in the organization of the developing brain. In 1998, immature neurons from the pyramidal neocortex and other regions of the immature brain showed membrane depolarizations of CR cells caused by GABA-A and glycine receptor activation.In 1994, a subpopulation of CR cells was shown to be GABAergic (using GABA as a transmitter). In 2003, CR cells in rodents and primates were shown to be glutamatergic (using glutamate as a transmitter). Immunohistochemical studies (detecting antigens by exploiting the principle of antibodies binding specifically to antigens in biological tissues) showed that CR cells expressed GABA-A and GABA-B receptors, ionotropic and metabotropic glutamate receptors, vesicular glutamate transporters, and a number of different calcium-binding proteins, such as calbindin, calretinin and parvalbumin. CR cells express several genes important in corticogenesis, such as reelin (RELN), LIS1, EMX2, and DS-CAM. CR cells selectively express p73, a member of the p53 family involved in cell death and survival.