Synaptotagmin genes on mouse chromosomes 1, 7, and 10 and human chromosome 19.

Abstract

The synaptotagmins (p65s) are abundant secretory vesicle membrane proteins with calcium and phospholipid binding domains that may function in calcium-dependent exocytosis in neurons and some endocrine cells. Mutations of synaptotagmin in C. elegans and Drosophila result in weakness and uncoordinated movement and are lethal (Nonet et al. 1993; Di Antonio et al. 1993). cDNAs encoding three isoforms of rat synaptotagmin have been cloned (Perin et al. 1990, 1991; Geppert et al. 1991; Mizuta et al. 1994). There is 40% overall amino acid sequence identity among the three proteins, concentrated in a region that is highly homologous to the C 2 regulatory domain of protein kinase C. The synaptotagmin genes are differentially expressed in various brain regions, Syt3 is also expressed in pituitary, thyroid, pancreatic islets, and several hormone-secreting cell lines (Mizuta et al. 1994). To evaluate the synaptotagmins as candidate genes for mouse neurological mutants, we mapped the three mouse synaptotagmin genes, using the rat cDNAs and two interspecific backcrosses. Restriction fragment length polymorphisms for Sytl, Syt2, and Syt3 were identified by digestion of genomic DNA from strains CAST/El, SPRET/Ei, and C57BL/6J (The Jackson Laboratory, Bar Harbor, Me.) and hybridization with cDNA probes (Table 1). The rat cDNA probes for Sytl (Perin et al. 1990), Syt2 (Geppert et ai. 1991; Perin et al. 1990), and Syt3 (Mizuta et al. 1994) were previously described. Primers for the Mit microsatellite markers (Dietrich et al. 1992) were obtained from Research Genetics (Birmingham, Ala.). Synaptotagmin 1 was previously localized to human Chromosome (Chr) 12 cen-q21 (Perin et ai. 1991), a region that includes two conserved groups on mouse Chrs 10 and 15. No linkage was observed between Sytl and markers for mouse Chr 15. However, analysis of markers from Chr 10 demonstrated linkage (Fig. 1A). The observed gene order and distances on distal region of mouse Chr 10 were: centromere-DlOMitlO-lO.7 +_ 5.8-Syti-10.7 + 5.8DlOMit136-7.1 +_ 4.9-DlOMitl4. Sytl is thus located within the large conserved linkage group on human Chr 12 and mouse Chr 10 that includes the region between phenylalanine hydroxylase and Erbb3 (Taylor et al. 1993). Recent mapping of two neurological mutants in this region, grizzled and jittery, relative to molecular markers (Kapfhamer and Burmeister, 1994) indicates that Sytl is located distal to both. On the basis of the reported linkage of Syt2 to the renin gene in the rat, we tested linkage between Syt2 and markers near Renl on mouse Chr 1 (Fig. 1B). The following gene order and distances were observed: centromere-D1Mit5-19.2 +_ 7.7-D1Mit140-11.5 +_ 6.3-Syt2-15.4 + 5.0-D1Mit37. Syt2 thus maps to a conserved linkage group on mouse Chr 1 and human Chr lq that includes 39 mapped genes (Seldin et al. 1993). Since no mapping data were available for Syt3, we probed The