Spatiotemporal distribution of tenascin-R in the developing human cerebral cortex parallels neuronal migration.

Tenascin-R is an extracellular matrix glycoprotein that is restricted to the central nervous system, where it acts as a multifunctional and versatile molecule. We report spatial and temporal distribution of tenascin-R in the developing human cerebral cortex for the first time. At 7.5 gestational weeks (GW), tenascin-R was expressed in a restricted area of the basal telencephalon. At 9.5 and 11 GW, it showed a unique double band expression pattern that delineated the boundaries of the future cortical plate. From 14 to 30 GW, tenascin-R labeling extended to the whole cortex from the deep layers toward the marginal zone with an inside-to-outside progression pattern reminiscent of neuronal migration. Moreover, tenascin-R labeling initially appeared in the form of thin, straight, or slightly tortuous intercellular processes directed toward the surface in parallel with the axis of neuronal migration. At the end of pregnancy and at adulthood, diffuse and homogeneous immunolabeling of the whole cortex thickness was observed. The striatum and thalamus were faintly positive for TNR as early as 14 GW, and this positivity intensified with brain maturation. At all developmental stages, the germinative zone, the corpus callosum, the anterior commissure, and the internal capsule appeared clearly negative for tenascin-R immunostaining whereas the adjacent parenchyma was immunopositive. Our results show that tenascin-R expression is tightly regulated in a spatiotemporal manner during brain development, especially cortical plate formation. Its pattern of expression suggests a role for tenascin-R in corticogenesis.