Reeler

A reeler is a mouse mutant, so named because of its characteristic "reeling" gait. This is caused by profound hypoplasia of the mouse's cerebellum, in which the normal cerebellar folia are missing. The mutation is autosomal and recessive.

Cortical neurons are generated normally but are abnormally placed, resulting in disorganization of cortical laminar layers in the CNS. The reason is the lack of Reelin, an extracellular matrix glycoprotein, which during the corticogenesis is secreted mainly by the Cajal-Retzius cells. In the reeler neocortex, cortical plate neurons are aligned in a practically inverted fashion (‘‘outside-in’’). In the ventricular zone of the cortex fewer neurons have been found to have radial glial processes. In the dentate gyrus of hippocampus, no characteristic radial glial scaffold is formed and no compact granule cell layer is established. Therefore, the reeler mouse presents a good model in which to investigate the mechanisms of establishment of the precise neuronal network during development.

There are two types of the reeler mutation:

In order to unravel the reelin signaling chain, attempts are made to cut the signal downstream of reelin, leaving reelin expression intact but creating the reeler phenotype, sometimes a partial phenotype, thus confirming the role of downstream molecules. The examples include:

Heterozygous reeler mice, also known as HRM, while lacking the apparent phenotype seen in the homozygous reeler, also show some brain abnormalities due to the reelin deficit.

Heterozygous (rl/+) mice express reelin at 50% of wild-type levels and have grossly normal brains but exhibit a progressive loss during aging of a neuronal target of reelin action, Purkinje cells.

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