Xenopus tropicalis oocytes as an advantageous model system for the study of intracellular Ca2+ signalling

1 The purpose of this study was to compare oocytes from the pipid frogs Xen opus tropicalis and Xenopus laevis, with respect to their utility for study ing Ca2+ signalling mechanisms and for expression of heterologous proteins. 2 We show that X. tropicalis oocytes possess an intracellular Ca2+ store th at is mobilized by inositol (1,4,5) trisphosphate (IP3) Ca2+ signalling is activated by endogenous lysophosphatidic acid receptors and cytosolic Ca2activates a plasma membrane chloride conductance. The spatiotemporal organi zation of cytosolic Ca2+ signals, from the microscopic architecture of elem entary Ca2+ 'puffs' to the macroscopic patterns of Ca2+ spiking are closely similar to the local and global patterns of Ca2+ release previously charac terized in oocytes from X, laevis. 3 By injecting X. tropicalis oocytes with cDNA encoding an ER-targeted fluo rescent protein construct, we demonstrate the capacity of the X. tropicalis oocyte to readily express heterologous proteins. The organization of ER is polarized across the oocyte, with the IP3-releaseable store targeted withi n an similar to8 mum wide band that circumscribes the cell. 4 We conclude that the X. tropicalis oocyte shares many of the characterist ics that have made oocytes of X. laevis a favoured system for studying Ca2 signalling mechanisms. Moreover, X. tropicalis oocytes display further pra ctical advantages in terms of imaging depth, Ca2+ signal magnitude and elec trical properties. These further enhance the appeal of X, tropicalis as an experimental system, in addition to its greater amenability to transgenic a pproaches.