Evolutionary conservation of vitellogenin genes.

Homologous and heterologous hybridizations in solution were performed between sheared genomic DNA and DNA complementary to vitellogenin mRNA of Xenopus, chicken, and migratory locust. The kinetics of hybridization and the thermal stability of the hybrids formed suggested a high degree of conservation of coding sequences of insect, amphibian, and avian vitellogenin genes. These cDNA probes hybridized to calf thymus DNA to a slight, but significant, extent, and not at all to Micrococcus lysodektikus DNA. DNA complementary to Xenopus albumin mRNA did not cross-hybridize significantly with locust or chicken DNA. Further evidence for the evolutionary conservation of vitellogenin genes was obtained from Southern blot analysis of restriction endonuclease-digested genomic DNA from a variety of vertebrate and invertebrate oviparous animals (Xenopus, chicken, migratory and desert locusts, yellow meal worm, carab moth, and Mediterranean fruitfly). When probed with cloned vitellogenin cDNAs from Xenopus and migratory locust, the DNA of these organisms showed varying degrees of homology of parts of the vitellogenin coding sequences. Southern blot analysis also showed that a part of the sequence specified in the cloned Xenopus vitellogenin cDNA was represented as repetitive DNA in the locust genome. However, cloned locust vitellogenin cDNA hybridized to discrete fragments of the restricted vertebrate DNA. These studies demonstrate a remarkably high degree of conservation of insect, amphibian, and avian vitellogenin genes.