Transglutaminase forms midkine homodimers in cerebellar neurons and modulates the neurite-outgrowth response.

Midkine is a prominent acyl donor substrate for the protein cross-linking enzyme transglutaminase type 2 in rat brain neurons. Transglutaminase type 2 and midkine immunoreactivity are regionally colocalized in developing cerebellar cortex. Monomeric midkine is present in the embryonic dorsal rhombic lip which gives rise to the cerebellar cortex. A high-molecular weight (29-30 kDa) midkine appears during postnatal cerebellar development. The presence of the high-molecular weight midkine in cultured cerebellar cortical interneurons is dependent upon culture conditions. Transglutaminase catalyzes the calcium-dependent cross-linking of midkine predominantly into 29-30 kDa dimers. Dimer-formation of midkine in vitro and in cultured neurons is reduced in the presence of a transglutaminase inactivator. Neurons plated onto previously cross-linked midkine exhibit larger growth cones and enhanced neurite outgrowth compared to those plated onto monomeric midkine alone.