Regulation of Semaphorin III/Collapsin-1 Gene Expression during Peripheral Nerve Regeneration R. Jeroen Pasterkamp, Roman J. Giger, and Joost Verhaagen Graduate School for Neurosciences Amsterdam, Netherlands Institute for Brain Research, Meibergdreef 33, 1105 AZ Amsterdam-ZO, The Netherlands Received February 26, 1998; accepted June 26, 1998 The competence of neurons to regenerate depends on their ability to initiate a program of gene expres- sion supporting growth and on the growth-permissive properties of glial cells in the distal stump of the injured nerve. Most studies on intrinsic molecular mechanisms governing peripheral nerve regeneration have focussed on the lesion-induced expression of proteins promoting growth cone motility, neurite exten- sion, and adhesion. However, little is known about the expression of intrinsic chemorepulsive proteins and their receptors, after peripheral nerve injury and dur- ing nerve regeneration. Here we report the effect of peripheral nerve injury on the expression of the genes encoding sema III/coll-1 and its receptor neuropilin-1, which are known to be expressed in adult sensory and/or motor neurons. We have shown that peripheral nerve crush or transection results in a decline in sema III/coll-1 mRNA expression in injured spinal and facial motor neurons. This decline was paralleled by an induction in the expression of the growth-associated protein B-50/GAP-43. As sema III/coll-1 returned to normal levels following nerve crush, B-50/GAP-43 re- turned to precrush levels. Thus, the decline in sema III/coll-1 mRNA coincided with sensory and motor neuron regeneration. A sustained decline in sema III/ coll-1 mRNA expression was found when regeneration was blocked by nerve transection and ligation. No changes were observed in neuropilin-1 mRNA levels after injury to sensory and motor neurons, suggesting that regenerating peripheral neurons continue to be sensitive to sema III/coll-1. Therefore we propose that a decreased expression of sema III/coll-1, one of the major ligands for neuropilin-1, during peripheral nerve regeneration is an important molecular event that is part of the adaptive response related to the success of regenerative neurite outgrowth occurring following peripheral nerve injury.  1998 Academic Press Key Words: axonal regeneration; B-50/GAP-43; dorsal root ganglion; motor neuron; neuropilin; peripheral nerve; semaphorin/collapsin. INTRODUCTION Nerve fibers of the adult mammalian peripheral nervous system (PNS) are capable of long distance regeneration, while neurons of the mature central nervous system (CNS) do not usually regenerate. Suc- cessful regeneration depends on the intrinsic ability of neurons to initiate a program of gene expression that supports neurite growth and on the properties of the injured neural tissue distal to the lesion (reviewed in 62, 63). Peripheral axotomy induces the expression of proteins thought to promote regeneration, including c-jun and junD (24, 26, 37), B-50/GAP-43 (4, 25, 64, 74), and actin and tubulin (25, 71, 72). Schwann cells in injured peripheral nerves fascilitate regeneration of peripheral nerve fibers by clearing myelin debris (67) and upregulating the expression of neurotrophins and cell-adhesion molecules (16, 43, 46). In contrast, repul- sive proteins like sulfated proteoglycans, tenascin, and the oligodendrocyte-associated proteins NI-35 and NI- 250 are associated with the inhibition of regenerative neurite outgrowth in the CNS (5, 9, 36, 44, 57, 65, 84; for reviews, see 7, 59, 66). The notion that inhibitory guidance mechanisms are involved in the patterning of developing neuronal pro- jections (e.g., 9, 12, 13, 27, 35, 40, 51, 55, 77; for reviews, see 20, 70) has significantly contributed to the identifi- cation of an expanding number of repulsive proteins in the adult PNS and CNS, including members of the ephrin, Eph receptor, netrin, and semaphorin gene families (e.g., 1, 17, 18, 39, 42, 48, 83). It has been proposed that the presence of these chemorepulsive proteins in the adult nervous system could significantly influence the course of neuroregeneration (18, 19, 32, 40, 68, 75); however, the expression of these proteins after lesions has not been studied yet. Here we examine the expression of one of the sema- phorins, semaphorin III/collapsin-1 (sema III/coll-1), and its receptor neuropilin-1, following peripheral nerve injury. The semaphorins/collapsins comprise a family of chemorepulsive proteins that are expressed in discrete neuronal populations of the developing and mature EXPERIMENTAL NEUROLOGY 153, 313–327 (1998) ARTICLE NO. EN986886 313 0014-4886/98 $25.00 Copyright  1998 by Academic Press All rights of reproduction in any form reserved.