Five woolly mammoths, deep-frozen for millennia in the Siberianperma-frost, are among the animal models testing the power of fossilDNA to reconstruct ancient gene sequences.Two groups of molecular paleontologists from Russia, Germany andBritain report separately in the current issue of Nature on mitochondrialsequence similarities between these extinct pachyderms, Mammuthusprimigenius and elephants alive today in Africa (Loxodonta africana)and Asia (Elephas maximus).Writing in the journal's "Scientific correspondence" pages, one groupconcluded: "Sequencing data from additional informativemitochondrial DNA regions and a larger number of individuals fromboth the living and extinct genera, are needed before the evolutionaryrelationships of the elephantids can be fully understood."This team, of which the first author is biological anthropologist ErikaHagelberg of Cambridge University, reported analyzing bone samplesfrom two Siberian mammoths at least 47,000 years old, by amplifyingand sequencing a fragment of the cytochrome b gene (which takes partin the mitochondrion's energy transfer). They cut the two 0.7-grambone samples from frozen carcasses at the Zoological Institute in St.Petersburg.One, the "Khatanga mammoth," yielded an age greater than 47,000years by accelerated mass spectrometry radiocarbon dating. The teamdated the second specimen to "not less than 150,000 years before thepresent," on the basis of associated fossil remains of an extinctlemming.Polymerase chain reaction amplification, against a 375-base-paircytochrome b fragment, took place, prudently, in "a laboratory whereelephant DNA had not been handled before."The resulting sequence comparisons could neither confirm nor deny adecade-old report by others that 99 percent homology of the mammothand modern elephant sequences suggest "an evolutionary divergencebetween three and five million years ago." Hence theirrecommendation for additional expanded trials.That same Khatanga carcass, along with three others, contributed soft-tissue samples to a four-mammoth analysis performed by otherscientists from the zoology institutes in St. Petersburg and Munich,Germany, led by Matthias Hoss, reported in the same issue of Nature.These range in age from 9,700 to more than 50,000 years before thepresent, and yielded retrievable DNA from seven samples. Theinvestigators compared these sequences not only to modern elephantsbut to bovine and equine ungulates as well. Enzymatic amplification ofa fragment of a mitochondrial 16S ribosomal RNA gene indicated thatmammoths and modern elephants differ by up to four basesubstitutions, and by six to 12 for the other two ungulates.Moreover, the four mammoths' sequences vary from each other by upto five substitutions, against only two between the African and Asianmodels. This suggests that the extinct Siberians were highly diverse intime and space. The writers propose that "the much older sequencesreported in the past few years, for example in amber, be submitted tothe same kind of tests . . ."To which microbiologist Raul Cano responds, "I submit that they havebeen." He told BioWorld Today, that the authors of the letters inNature "have to read my article in the June 1994 issue of Applied andEnvironmental Microbiology, titled "Bacillus DNA in Fossil Bees: anAncient Symbiosis?"This reports analysis of bacteria in the guts of four stingless beespreserved for some 40 million years in Dominican Republic amber.Cano, who is chairman of microbiology at California Polytechnic StateUniversity in San Luis Obispo, Calif., focuses on amber and host-parasite relationships.Last year he extracted and analyzed DNA from an ancient insectentombed in amber 120-135 million years ago, about the time the filmJurassic Park popularized the concept of amber-derived DNA. (SeeBioWorld Today, June 10, 1993, p. 1.) n081294
-- David N. Leff Science Editor
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