Northern blot and in situ hybridization analyses for the development of myristoylated alanine-rich c-kinase substrate mRNA in the monkey cerebral cortex.

Myristoylated alanine-rich C-kinase substrate (MARCKS) is a major neuron-specific substrate for protein kinase C, and is involved in both neurite outgrowth and synaptic plasticity. Using both Northern blot and in situ hybridization techniques, we investigated whether the expression of MARCKS mRNA in the monkey cerebral neocortex and hippocampus changed during the developmental period. In each of four neocortical areas examined, i.e. the prefrontal area (area FD of [Illinois Monographs in the Medical Sciences (1947) 1]), the temporal association area (TE), the primary somatosensory area (PB), and the primary visual area (OC), the Northern blot analysis showed that the amount of MARCKS mRNA was high during the fetal and early postnatal periods, and decreased sharply between postnatal day 70 and postnatal month 6. The in situ hybridization experiments showed that the expression of MARCKS mRNA was decreased in every layer of neocortical areas at postnatal month 6 or later. In the primary sensory areas (areas PB and OC), the degree of decrease was higher in the supragranular layers (layers II and III) than in the infragranular layers (layers V and VI). In the hippocampus, the developmental change in the amount of MARCKS mRNA was small, but the in situ hybridization revealed a prominent decrease in Ammon's horn in monkeys on postnatal month 8 and later. These findings indicate that region-specific expression of MARCKS mRNA is established around postnatal month 6. We suggest that the extensive expression of MARCKS mRNA is one of the molecular bases of high plasticity in the infant cerebral cortex.