ETV4 and Infertility: Pea3 knock-out mice, however, did not seem to have any major effects, except for ejaculation dysfunction in males, although it is suspected that the infertility of pea3-/- males may have an underlying neuronal basis, particularly since Pea3 is expressed in specific bundles of motor neurons that innervate limb muscles and in afferent sensory neurons of these same muscles and it is conceivable that Pea3 is also expressed in neurons that innervate the penis (Laing et al., 2000).