Essential role of protein kinase B gamma (PKB gamma/Akt3) in postnatal brain development but not in glucose homeostasis.

Protein kinase B is implicated in many crucial cellular processes, such as metabolism, apoptosis and cell proliferation. In contrast to Pkb α and Pkb β-deficient mice, Pkb γ-/- mice are viable, show no growth retardation and display normal glucose metabolism. However, in adult Pkb γ mutant mice, brain size and weight are dramatically reduced by about 25%. In vivo magnetic resonance imaging confirmed the reduction of Pkb γ-/- brain volumes with a proportionally smaller ventricular system. Examination of the major brain structures revealed no anatomical malformations except for a pronounced thinning of white matter fibre connections in the corpus callosum . The reduction in brain weight of Pkb γ-/- mice is caused, at least partially, by a significant reduction in both cell size and cell number. Our results provide novel insights into the physiological role of PKBγ and suggest a crucial role in postnatal brain development.