Maternal and cytoplasmic inheritance of mitochondrial DNA in Xenopus

Abstract

The inheritance of mitochondrial DNA (mtDNA 1) has been studied in the progeny of an interspecific cross of the amphibians Xenopus laevis and Xenopus mulleri. The mtDNAs of these two species were distinguished by molecular hybridization with cRNA transcribed from the mtDNA of the two species. F 1 hybrid frogs from either reciprocal cross always contained only maternal mtDNA. Therefore, the mitochondria in somatic cells of the progeny are derived from the numerous mitochondria in the egg. Large oocytes in F 1 hybrid frogs, or embryos obtained by backcrossing female F 1 hybrids to parental animals, contained mtDNA derived from the original female parent. These experiments show that mtDNA is inherited cytoplasmically and maternally in Xenopus. Molecular hybridization of nuclear DNA and cRNA transcribed from mtDNA was used to test the question whether copies of the mitochondrial sequences exist in the nucleus. Contamination of nuclear DNA preparations by cytoplasmic mtDNA was excluded by looking for paternal mtDNA sequences in nuclear DNA preparations from hybrid animals. Since no paternal sequences were found we conclude that the nucleus does not contain a “master copy” of the mitochondrial sequences.