CLASP (CLASP1 or CLASP2) acts positively downstream of ABL (ABL1 or ABL2) as part of the repellent response initiated by activation of ROBO1. CLASP is spatially positioned to interact with ROBO receptors. SLIT mediated repulsion results in activation of CLASP, presumably through its phosphorylation by the ABL kinase. Activation of CLASP in turn results in inhibition of microtubule polymerization on the side of the growth cone receiving the repulsive signal and consequently the growth cone turns to the opposite side. A direct link between ABL and CLASP, notably the mechanism of CLASP activation, has not been demonstrated, however (Wills et al. 2002, Lee et al. 2004, Kalil and Dent 2004).