Developmental basis of pronephric defects in Xenopus body plan phenotypes

We have used monoclonal antibodies that recognize the pronephric tubules or pronephric duet to explore the induction of the embryonic kidney in develo ping Xenopus embryos. Morphogenesis of the pronephros was examined in UV-ve ntralized and lithium-dorsalized embryos. We find that the pronephric tubul es are present in all but the strongest UV-induced phenotypes, but absent f rom relatively moderate lithium phenotypes. Interestingly the pronephric du ct, which develops from the ventroposterior portion of the pronephric anlag e, is missing from more of the mild UV phenotypes than are pronephric tubul es. The loss of the capacity to form pronephroi in UV-ventralized embryos i s caused by the loss of tissues capable of inducing the pronephric mesoderm , as marginal zone explants from ventralized embryos are still competent to respond to pronephric-inductive signals. Explant recombination experiments indicate that the tissue responsible for both the loss of pronephroi in UV -ventralized embryos and the induction of pronephroi during normal developm ent is the anterior somites. The absence of pronephroi in relatively mild l ithium phenotypes has a developmental basis different from that of the UV p henotype, as explants from lithium-treated embryos are effective inducers o f pronephroi in recombinants with competent mesoderm, even though they them selves do not form pronephroi in isolation. Together these data indicate th at dorsal tissues, especially the anterior somites, are responsible for the establishment of the intermediate mesoderm and the induction of the embryo nic kidneys and that even mild dorsalization destroys the capacity to form cells competent to receive this signal. (C) 1999 Academic Press.