(Solved): Our limbs contain fexor and extensor muscles (e.g, bicep and tricep). Their coordinated contraction ...

Our limbs contain fexor and extensor muscles (e.g, bicep and tricep). Their coordinated contraction and relacation are required for smooth limb movements. Thus. the flexor and extensor need to be innervated by distinct populations of motor neurons so that they do not contract simultaneously. The cell bodies of the limb motor neurons are in the spinal cord. During development, motor axons grow along the body wall and limb mesenchyme to reach their specihc target muscles. Ephrin-Eph signals are involved in the guidance of motor axons. There are two classes of ephrins: ephrin A and ephrin B. Each uses a specific set of receptors. The receptors for ephrin A are named EphA; the receptors for ephrin B are EphB, During limb development, ephrin A is expressed in the ventral half of the limb bud and ephrin B is in the dorsal half. The expression patterns of Eph receptors in the limb motor avons are shown in the figure below. (NF: neurofilament, marking all axon bundies; D; dorsal region of the limb bod: V: ventral region of the limb bud) 1: Using the intormation provided above, please derive a hypothesis for the molecular mechanism by which the observed growth partern of motor axons in the limb is generated (5 points) 2. Under your hypothesis, what is the expected growth pattem of a limb motor axon expressing both fohA4 and EphB1? (2 points) Why? (3 points)