ANALYSIS OF SYNAPTOTAGMIN I-IV MESSENGER-RNA EXPRESSION AND DEVELOPMENTAL REGULATION IN THE RAT HYPOTHALAMUS AND PITUITARY

Synaptotagmins are a large family of synaptic vesicle membrane protein s, that appear to be involved in neurotransmitter secretion from small secretory vesicles. We have quantitatively analysed the messenger RNA levels of synaptotagmin I-IV isoforms in adult hypothalamic and pitui tary tissues in order to determine which of: these isoforms dominate i n these tissues which mainly secrete peptides from large dense core ve sicles. We also studied the expression of these isoforms during prenat al (E15, and E17) and postnatal (P1, P7, P14 and P21) rat hypothalamic development. In order to assay small individual samples (e.g., pituit ary and embryonic tissues). we employed quantitative reverse transcrip tion-polymerase chain reaction methods. Our results show that synaptot agmin I messenger RNA is the most abundant isoform in all tissues, and is about 5.4- or 38-fold higher in hypothalamus than in neurointermed iate and anterior pituitary lobe, respectively. Synaptotagmin II. whic h is very abundant in cerebellum, is relatively low in hypothalamus (5 % of cerebellum) and virtually absent from the pituitary. Synaptotagmi n III is about 10 times greater in the neural tissues versus the pitui tary, and synaptotagmin IV was the least abundant isoform in all the t issues. Developmental analyses of the synaptotagmin isoforms in rat hy pothalamus shows that all isoforms are at low levels during embryonic stages and increase postnatally. Synaptotagmin I and II have similar p atterns and rise to maximum (adult) levels around P14, whereas synapto tagmin III and IV I each their maximum levels considerably earlier, at P1. These data show that synaptotagmin I is the dominant isoform in b oth predominantly peptide secreting systems (e.g., in pituitary tissue s) and in neurotransmitter secreting systems (e.g., in cerebellum). Wh ile the developmental expression patterns of synaptotagmin I and II pa rallels the temporal development of synaptogenesis in the nervous syst em, the early maximal expression of synaptotagmin III and IV suggests that these isoforms may have other functions during early postnatal de velopment.