SYNAPTOTAGMIN-I AND 1B4 ARE IDENTICAL - IMPLICATIONS FOR SYNAPTOTAGMIN DISTRIBUTION IN THE PRIMATE BRAIN

We have determined that the human cDNA sequence of the previously desc ribed primate brain mRNA species 1B4 is nearly identical (99.95% simil arity) to that of human Synaptotagmin I. The apparent identity of Syna ptotagmin I with 1B4, whose distribution in the brain of the monkey Cy nomolgous was determined previously by Northern blot and in situ hybri dization (ISH) analyses, reveals that Synaptotagmin I is differentiall y expressed in the. primate brain. Primate Synaptotagmin I mRNA is enr iched in hindbrain structures relative to forebrain structures by Nort hern blot analysis. By ISH analysis, primate Synaptotagmin I mRNA is h ighly expressed in occipital cortex and lateral geniculate (visual sys tem components) and differentially expressed across topographic cortic al boundaries between inferior and superior temporal gyrus (a polymoda l zone with visual, auditory and somatosensory inputs) and between are as 17 and 18 of the visual cortex (primary and secondary visual areas) . Cortical expression is also enriched in layers V and VI, which conta in large pyramidal projection neurons, Synaptotagmin I's greater assoc iation with large projection neurons and with some components of visua l sensory transduction could reflect a requirement of these neural com ponents for greater synaptic activity. Synaptotagmin I expression in t he primate brain is also dissimilar to Synaptotagmin I expression in r odents. Thus, variation of Synaptotagmin I expression has occurred dur ing mammalian evolution, perhaps as a consequence of the larger size a nd neurotransmitter requirements of primate neurons.