The microstructure of GaN layers grown on Si(110) is studied by transmission electron microscopy. The GaN layers were grown by metal-organic vapor phase epitaxy using low-temperature AlN interlayers and a high-temperature AlN seed layer. Anisotropic misfit strain originating at the AlN/Si(110) interface is notably reflected in the microstructure of the GaN layers. The stress produced in GaN/Si(110) films is relieved by bending of edge type threading dislocations over the basal plane, generating horizontal segments aligned all along the closely lattice matched direction [100]. It is proposed that the horizontal defects are generated by a driven force with glide- and climb-components manifested on some of the prismatic slip planes of GaN. The general mechanism of the change in the propagation direction of dislocations is discussed.