Comparison of RNA localization during oogenesis within Acipenser ruthenus and Xenopus laevis [Xenopus laevis]

In this study we analyzed the spatial and temporal localization of maternal transcripts during oogenesis in Xenopus laevis. The occurrence of transcript asymmetry in X. laevis has been described at a global level only in matured eggs, while the establishment of the asymmetry during oogenesis has been described only for a few transcripts. In this model it was discerned that there exist three pathways (early, intermediate, late) for the establishment of the vegetal gradient, while for the animal gradient not much is known for its production. In this study we assessed the temporal establishment of the transcript localization at a global level for Xenopus laevis. We were able to determine that there are many transcripts that show temporal variability in the establishment of their localization. We observed the previously described early, intermediate (predefined) and also late pathways but found more member transcripts within these groups. We also described, perhaps for the first time, an early, intermediate (predefined) and late pathway for the animal genes as well. Additionally, we showed that some maternal transcripts are dynamic during oogenesis with degradation and de novo production being observed. Our study showed that in additional to spatial orientation to the transcripts, there is a strong temporal factor. The discovery of these new temporal profiles should help to better understand the driving forces during embryogenesis. Overall design: Oocytes from Xenopus laevis females were extracted to create four groups: very small oocytes (n = 3; stage III, size 560-580µm); small oocytes (n = 5; stage IV, size 720-810µm); medium (n =2; stage V, size 1050µm); and big (n = 2; stage VI, size 1140-1200µm). Samples were oriented along their animal-vegetal axis and cryosectioned to produce 5 main sections (A (extreme animal) – E (extreme vegetal)). Each section was sequenced and the abundance of the transcript across the section and stages analyzed.