Fig. 5. Four connexins were maternally expressed in Xenopus embryos. (A) RT-PCR from ovary, oocytes and early embryos distinguished between maternally and zygotically expressed Xenopus connexins. Cx30 was solely zygotic and Cx38 solely maternal. Cx31 and Cx43.4 were both maternal and zygotic. Histone H4 was used as an internal control. (B) RT-PCR analysis revealed that Cx43 RNA, but not Cx41, was expressed maternally in fertilized eggs and 64-cell stage embryos. RT-minus controls were utilized for all cDNA samples in A and B, but only one example is shown in each panel. (C) Steady-state levels of Cx38 and Cx43.4 RNA are compared by northern blots. Fibronectin (FN) levels are provided as a loading control. In all three panels oocytes samples were obtained from defolliculated oocytes and ovary samples from pieces of ovary containing follicular oocytes and ovarian tissue.