Neurotrophin-3 and other neurotrophic factors contribute to the development and maintenance of the vertebrate nervous system by promoting localized neuronal survival. The human gene encoding neurotrophin3, a highly conserved protein with complete amino acid identity in human, mouse, and rat, has been mapped to Chromosome (Chr) 12p13 (Maisonpierre et al. 1991). The mouse homolog, Ntf-3, was assigned to Chr 6 by use of a somatic cell panel (Ozcelik et al. 1991). We undertook the regional localization of Ntf-3 in order to test it as a candidate for the mnd2 mutation which we recently mapped to Chr 6; homozygosity for mnd2 results in motor neuron disease due to degeneration of spinal motor neurons (Jones et al. 1993). von Willebrand factor is a glycoprotein involved in blood coagulation that is both a carrier for factor VIII (antihemophilic factor) and a mediator of plateletvessel wall interaction (Ginsburg and Bowie 1992). The human gene VWF (previous symbol F8VWF) is the most distally mapped gene on Chr 12p13.3 (NIH/CEPH Collaborative Mapping Group 1992). The locations of NTF3 and VWF suggested that they might be members of the conserved linkage group on mouse Chr 6 that includes 11 other genes from human 12p1213 (Nadeau et al. 1992; Elliott and Moore 1992). Ntf-3 was mapped by Southern blot analysis with a BgllI RFLP between strains C57BL/6J (3.6 kb) and SPRET/Ei (9.7 kb; Fig. 1). The Ntf-3 probe was a 550bp genomic fragment that was amplified from genomic DNA from strain C57BL/6J with primers based on the published nucleotide sequence (Hohn et at. 1990): primer 1, 5' (+250) AGG AGT TTG CCG GAA GAC TCT CTC AAT TCC (+279) 3'; and primer 2, 5' (+ 799) GCA ACC GTT TTT GAC CGG CCT GGC