CALCIUM REGULATION AND CALCIUM FUNCTION IN THE NUCLEUS OF STARFISH OOCYTES

The nucleus (germinal vesicle) of starfish oocytes can be injected in vivo to introduce into it calcium indicators and various effecters or inhibitors of calcium signalling pathways. This is advantageous to the study of the debated problem of nuclear calcium homeostasis, which is related to that of the function of calcium in the nucleus. The work d escribed here has shown that, at variance with other cell types, the n uclear envelope of starfish oocytes is relatively impermeable to calci um and to calcium sensitive dyes. It has also shown that a rise in fre e nuclear calcium is required for the reinitiation of meiosis induced by 1-methyladenine. Both inositol 1,4,5-trisphosphate (InsP(3)) and cy clic ADP-ribose (cADPr) receptors are present and functional in the me mbrane enveloping the nucleus. The chief processor of the calcium sign al, calmodulin, interacts in the nucleus with the heterogeneous ribonu cleoprotein particles and could thus play an important role in the pro cessing of pre-mRNA.