Dna sequence of the mitochondrial hypervariable region ii (krings et al.)
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1) The authors determined the DNA sequence of the second hypervariable region (HVRII) of mitochondrial DNA from the Neandertal type specimen. 2) When combined with the previously published HVR1 sequence, phylogenetic analysis found the Neandertal mtDNA to fall outside the variation of contemporary human mtDNA sequences. 3) The estimated date of divergence between Neandertal and modern human mtDNA sequences was 465,000 years before present, with a confidence interval of 317,000 to 741,000 years. This supports the Neandertals having a separate evolutionary history from modern humans.
Dna sequence of the mitochondrial hypervariable region ii (krings et al.)
- 1. DNA sequence of the mitochondrial hypervariable region II from the Neandertal type specimen Matthias Krings, Helga Geisert, Ralf W. Schmitz, Heike Krainitzki, and Svante Pääbo PNAS 1999;96;5581-5585 doi:10.1073/pnas.96.10.5581 This information is current as of January 2007. Online Information High-resolution figures, a citation map, links to PubMed and Google & Services Scholar, etc., can be found at: www.pnas.org/cgi/content/full/96/10/5581 References This article cites 20 articles, 10 of which you can access for free at: www.pnas.org/cgi/content/full/96/10/5581#BIBL This article has been cited by other articles: www.pnas.org/cgi/content/full/96/10/5581#otherarticles E-mail Alerts Receive free email alerts when new articles cite this article - sign up in the box at the top right corner of the article or click here. Rights & Permissions To reproduce this article in part (figures, tables) or in entirety, see: www.pnas.org/misc/rightperm.shtml Reprints To order reprints, see: www.pnas.org/misc/reprints.shtml Notes:
- 2. Proc. Natl. Acad. Sci. USA Vol. 96, pp. 5581–5585, May 1999 Evolution DNA sequence of the mitochondrial hypervariable region II from the Neandertal type specimen MATTHIAS K RINGS*, HELGA GEISERT*, RALF W. SCHMITZ†, HEIKE K RAINITZKI‡, AND SVANTE PAABO*§ ¨¨ *Max Planck Institute for Evolutionary Anthropology, Inselstrasse 22, D-04103 Leipzig, Germany; †Landschaftsverband Rheinland, Rheinisches Amt fur ¨ Bodendenkmalpflege Rheinisches Landesmuseum, Bonn, Endenicher Strasse 133, D-53115 Bonn, Germany; and ‡Hohere Berufsfachschule fur ¨ ¨ praparationstechnische Assistenten, Markstrasse 185, D-44799 Bochum, Germany ¨ Edited by L. L. Cavalli-Sforza, Stanford University School of Medicine, Stanford, CA, and approved February 17, 1999 (received for review December 28, 1998) ABSTRACT The DNA sequence of the second hypervari- lyzed the relationship of the combined sequences to the able region of the mitochondrial control region of the Nean- contemporary human mtDNA gene pool. dertal type specimen, found in 1856 in central Europe, has been determined from 92 clones derived from eight overlap- MATERIALS AND METHODS ping amplifications performed from four independent ex- tracts. When the reconstructed sequence is analyzed together Experimental Procedures. Sampling, precautions against with the previously determined DNA sequence from the first contamination, DNA extraction, PCR amplifications, cloning hypervariable region, the Neandertal mtDNA is found to fall of PCR products, and sequencing of clones were performed as outside a phylogenetic tree relating the mtDNAs of contem- described (5). Extracts A, B, and C were prepared previously porary humans. The date of divergence between the mtDNAs (5), whereas extracts D and E were prepared for this work from of the Neandertal and contemporary humans is estimated to 0.4 g of bone each. Extracts A, B, and C were known to yield 465,000 years before the present, with confidence limits of PCR products that contained various proportions of modern 317,000 and 741,000 years. Taken together, the results support human mtDNA sequences in addition to the Neandertal the concept that the Neandertal mtDNA evolved separately sequence (5). To test the degree of contamination of extracts from that of modern humans for a substantial amount of time D and E, PCRs were performed for a part of HVRI, which had and lends no support to the idea that they contributed mtDNA been determined previously (primers L16209 and H16271; ref. to contemporary modern humans. 5). The PCR products were cloned, and 10 clones each were sequenced. In both extracts, 8 of 10 clones carried 7 substitu- tions and an adenosine insertion was determined for the The role of Neandertals with respect to the evolution of Neandertal in this region (5), whereas two clones were iden- anatomically modern humans is controversial. Although some tical to the reference sequence (data not shown). Thus, as in paleontologists view Neandertals as a distinct branch in hom- the case of extracts A and B, a small proportion of contami- inid evolution that became extinct without any direct genetic nating sequences is present in extracts D and E. Extract C, contribution to present-day humans (1), others consider the which was prepared in another laboratory, contains a majority Neandertals to be among the direct ancestors of modern of contaminating modern human DNA (5). Thus, whenever Europeans (2). Recently, as a part of an interdisciplinary this extract was used, primers specific for putative Neandertal project of the Rheinisches Landesmuseum Bonn (3, 4), the sequences determined from adjacent segments were used (cf. DNA sequence of the first hypervariable region (HVRI) of the Fig. 1). There were 6, 2, and 19 clones derived from amplifi- mtDNA from the Neandertal type specimen was determined cations C21, C23, and E24 (Fig. 1), respectively, that contained (5). When compared with HVRI sequences of contemporary sequences with only one or no difference from the reference humans, the Neandertal mtDNA tended to fall outside the sequence (7). These clones (not shown) were considered variation of modern humans. Furthermore, phylogenetic anal- contaminants and were not included in the reconstruction of yses suggested that the Neandertal mtDNA was an outgroup the Neandertal sequence. For the other amplifications, all to the mtDNAs of modern humans, and the age of the most clones sequenced and the primers used are shown in Fig. 1. recent common ancestor (MRCA) of the mtDNAs of the Alignments and Sequence Analyses. For the analysis of the Neandertal and modern humans was estimated to be about HVRI and HVRII sequences, the Neandertal sequences were four times older than the age of the MRCA of modern human aligned to a data set of 663 contemporary mtDNA lineages, mtDNAs. These results indicate that the Neandertal mtDNA i.e., distinct mtDNA sequences found among 682 contempo- gene pool evolved for a substantial time period as an entity rary humans (8). All human sequences with ambiguities in the distinct from modern humans and give no indication that reported sequences were excluded before the analysis. In Neandertals contributed mtDNA to modern humans (5, 6). addition, nine mtDNA lineages from seven common chimpan- However, because these analyses were based on a DNA zees and two bonobos (‘‘pygmy chimpanzees’’) were used sequence of only 333 bp, the results are less than conclusive. (9–14). At positions where insertions deletions occurred be- For example, the support for the placement of the Neandertal tween the sequences of the apes, humans and the Neandertal mtDNA outside the variation of modern human mtDNA in the were excluded from the alignment. Sequence comparisons thus phylogenetic tree was merely 89% (5). To better estimate the were based on a total of 600 nucleotide positions, encompass- relationship of the Neandertal mtDNA to the current mtDNA ing positions 16024–16365 and 73–340, but excluding positions gene pool, we have determined 340 bp of the second mtDNA HVR (HVRII) from the Neandertal type specimen and ana- This paper was submitted directly (Track II) to the Proceedings office. Abbreviations: HVRI and HVRII, first and second hypervariable The publication costs of this article were defrayed in part by page charge region, respectively; MRCA, most recent common ancestor. Data deposition: The sequence reported in this paper has been payment. This article must therefore be hereby marked ‘‘advertisement’’ in deposited in the GenBank database (accession no. AF142095). accordance with 18 U.S.C. §1734 solely to indicate this fact. §To whom reprint requests should be addressed. e-mail: paabo@eva. PNAS is available online at www.pnas.org. mpg.de. 5581
- 3. 5582 Evolution: Krings et al. Proc. Natl. Acad. Sci. USA 96 (1999) 16078, 16166, 252, 291, 299, and 317–321 (numbering accord- stitutions was not found, although all four positions are ing to ref. 7). Pairwise sequence differences were calculated by variable among humans. using unpublished software by A. von Haeseler (Max Planck To determine the rest of the HVRII sequence, additional Institute for Evolutionary Anthropology Leipzig, Germany). amplifications partly overlapping with the above segment were The transition transversion ratio was estimated by using the performed from three different extracts, one of which had 663 human lineages and the program PUZZLE 4.0 (15), and been prepared in another laboratory (extract C, ref. 5). All genetic distances between pairs of sequences were calculated sequence positions from position 57 to 396 were scored by according to the F84 model using the ‘‘ML’’ option of the using 9–21 clones from at least two independent amplifica- program ‘‘dnadist’’ from the PHYLIP package (16). A neighbor- tions. Nucleotide states reproducible between amplifications joining tree (17) was produced by using the program ‘‘neigh- were inferred to exist in the original template molecules. bor’’ from PHYLIP, and the support for branches in this tree was Authenticity. The sequence determined was considered to calculated with the likelihood mapping option in PUZZLE 4.0 be derived from the mtDNA of the Neandertal individual for (18). For the estimation of the age of the MRCAs, pairwise the following reasons. (i) An analysis of the state of preser- genetic distances were calculated with the Tamura—Nei al- vation of amino acids in the bone (5) has shown that the gorithm (19) as implemented in PUZZLE 4.0. The parameters conditions under which the bone has been preserved are (transition transversion ratio), (purine pyrimidine transi- compatible with macromolecular preservation. (ii) The DNA tion ratio), and , which describes the distribution of the sequence could be amplified reproducibly from different evolutionary rates of individual nucleotide positions (20, 21), extracts. Because the amount of bone available for extractions were estimated from the human sequences by using PUZZLE 4.0. is limited, the HVRII sequence was not reproduced from an Means and SDs of the genetic distances within and between independent extract in another laboratory. However, this was species were calculated by using the program EXCEL 4.0. done for the HVRI sequence determined previously (5). For The rate of nucleotide substitution per position per year per the HVRII sequence, the extract prepared at Penn State lineage was calculated by the method of Tamura and Nei (19), University (extract C) yielded the same sequence as extracts using as a calibration point the divergence of humans and prepared in Munich. (iii) The DNA sequence falls as an chimpanzees 4–5 million years ago (22, 23). The upper and outgroup to modern human sequences in phylogenetic analy- lower confidence limits of this rate were estimated by using, ses (see below), an observation that may be taken to support respectively, the upper 95% confidence limit of the mean that it is derived from the bone. However, in some cases, genetic distance and the younger date for the human— divergent mtDNA sequences derived from amplifications of chimpanzee split, and the lower confidence limit of the genetic contemporary DNA containing nuclear insertions of mtDNA distance and the older date for the human—chimpanzee split. segments have been misidentified as ancient sequences (26). These two rates, in turn, were used to calculate the lower and Therefore, we designed a primer pair (NL152, cf. Fig. 1 and upper limits of the age of the MRCA of the human and NH243 5 -TGG CTG TGC A A CAT TTA GTC-3 ) that chimpanzee mtDNA gene pools. matches the sequence from the Neandertal type specimen and not contemporary human mtDNA sequences. Under amplifi- cation conditions that allow less than one copy of the Nean- RESULTS AND DISCUSSION dertal sequence per genome of human genomic DNA to be Retrieval of the Neandertal HVRII. Primers designed to amplified, these primers failed to produce products in ampli- amplify human and chimpanzee mtDNA sequences were used fications attempted from nine Africans, six Europeans, eight to amplify a 122-bp segment (including primers) of HVRII Asians, and three Australians Oceanians. This makes a nu- from extract B, prepared from the 0.4 g of the right humerus clear insertion an unlikely source of the sequence. (iv) If some of the Neandertal type specimen (24). A weak amplification form of miscoding DNA damage that was highly sequence- product could be visualized on an agarose gel. This product specific were prevalent in the Neandertal DNA molecules, this was reamplified and cloned in a plasmid vector, and the inserts would result in nucleotide substitutions that would be repro- of 13 clones were sequenced (Fig. 1, B18). All clones carried duced between independent amplifications and thus would be four identical substitutions from the contemporary human mistaken for substitutions in the authentic Neandertal DNA reference sequence (7). Furthermore, two other positions sequence. We consider this unlikely because 37 of 38 positions differed from the reference sequence in six and seven clones, in which a substitutional difference between the Neandertal respectively, and four more positions showed substitutions in and reference sequence are observed in HVRI and HVRII single clones. The same primers were used to amplify the same also show differences among modern humans, chimpanzees, DNA segment from a different extract (Fig. 1, D20). Among and bonobos. Because 295 of 600 positions studied are variable the seven clones sequenced, the four substitutions found in all in this data set, this would be an extremely unlikely result (P clones of the first amplification were found in all of these 1.13 10 11) if the substitutions in the Neandertal were clones, with the sole exception of a G at position 189 in one of generated by a process different from the process generating the clones. Neither the four singleton substitutions nor the two the differences in the contemporary species, for example, some substitutions observed in several clones from the first ampli- form of postmortem chemical damage. fication were seen among the clones from the second ampli- Sequence Comparisons. Among the 340 positions deter- fication. However, three more singleton substitutions were mined for HVRII, 11 transitional differences from the refer- observed at positions that showed no variation among the first ence sequence (7) were identified. In addition, an insertion of amplification. Substitutions that are not reproducible between three thymine residues occurs in a C-rich region after position amplifications are likely to be due to nucleotide misincorpo- 307 that shows length variation in humans (8). rations during the PCR, which may be induced by damage To estimate the relationship of the Neandertal mtDNA to present in ancient DNA (25). That two nonreproducible that of contemporary humans, positions 73–340 of HVRII substitutions occur in a large proportion of clones from one of were joined with positions 16024–16365 of HVRI and aligned the amplifications indicates that the amplifications start from to the homologous sequences from 151 Africans, 472 Euro- very few template molecules, a supposition that agrees with the peans, 41 Asians, 10 Native Americans, and 15 Australian quantitation performed previously (5). When the sequence Oceanians as well as 7 chimpanzees and 2 bonobos. Positions with the four substitutions seen in both amplifications was at which insertions deletions occurred were excluded. Some compared with a collection of 951 contemporary human humans shared the same sequences such that the data set could mtDNA control region lineages (8), this combination of sub- be collapsed to 663 different mitochondrial lineages.
- 4. Evolution: Krings et al. Proc. Natl. Acad. Sci. USA 96 (1999) 5583 Table 1. Pairwise sequence differences between the Neandertal, humans, and some apes Chimpanzees Humans Neandertal bonobos (n 663) (n 1) (n 9) Humans 10.9 5.1 35.3 2.3 93.4 7.1 (1–35) (29–43) (78–113) Neandertal 94.1 5.7 (84–103) Chimpanzees 54.8 24 bonobos (1–81) Shown are means SD and ranges (in parentheses) of pairwise sequence differences. The chimpanzee and bonobo DNA sequences used come from two P. troglodytes troglodytes, one P. troglodytes verus, four P. troglodytes spec., and two bonobos (Pan paniscus). The contemporary human mtDNA lineages differ at an average of 10.9 positions from one another and at 35.3 positions from the Neandertal (Table 1). Thus, on average, the Neandertal mtDNA has more than three times as many differences from modern human sequences as the latter have between them. In addition to the substitutions, the Neandertal sequences carry an insertion of an A after position 16263 in HVRI as well as the insertion of three T residues in HVRII. It may be noted that a small fraction (0.037%) of the inter- human comparisons are larger than the smallest distance (29 substitutions) between the Neandertal and humans. It has been suggested that Neandertals were among the direct ancestors of modern Europeans (2, 27). European mtDNAs therefore might be expected to have fewer nucleotide differences from the Neandertal mtDNA than mtDNAs from Africa or Asia. The modern human sequences from the different continents therefore were compared separately with the Neandertal sequence. The mtDNAs from Africa, Europe, and Asia were found to carry 34.4 2.7, 35.8 2.1, and 33.8 2.0 differences from the Neandertal sequence, respectively. The modern human lineages displaying the fewest differences (29 substitutions) to the Neandertal mtDNA were found in Africa, but the closest lineages in Asia and Europe were almost as similar to the Neandertal (30 and 31 differences, respec- tively). Thus, the mtDNA gene pools of modern humans on these continents are equidistant from the Neandertal mtDNA. Because of the stochastic nature of the accumulation of mutations and the heterogeneity of substitution rates among nucleotide positions, it is not surprising that some contempo- rary mtDNAs have fewer differences from the Neandertal mtDNA than the maximum number of differences seen among contemporary mtDNAs. This cannot be taken as an indication that these contemporary mtDNAs are more closely related in a phylogenetic sense to the Neandertal mtDNA than they are to other contemporary mtDNAs, as has been implied recently (28). Rather, phylogenetic analyses are needed to elucidate this question. Phylogenetic Analysis. The observed nucleotide differences among all pairs of sequences of the Neandertal, the 663 modern humans, and the 7 chimpanzees and 2 bonobos were FIG. 1. HVRII mtDNA sequences of clones derived from PCR products from Neandertal bone extracts. Dots indicate base identity to the human reference sequence (7). Clone designations are made up of a letter (B, C, D, E) that refers to DNA extracts followed by the number of the amplification performed and, after the dot, the number of the individual clones. Primers used are given for the first clone of each PCR. Numbers in primer designations indicate the number of the 3 base according to ref. 7, and L and H refer to the light and heavy strands of mtDNA. The sequences of the H primers are reverse and complemented. Standard designations are used for unidentified bases. The numbers of the positions at which substitutions in the Neandertal were found are indicated.
- 5. 5584 Evolution: Krings et al. Proc. Natl. Acad. Sci. USA 96 (1999) corrected for multiple substitutions, and a phylogenetic tree the two bonobos was calculated as 2,844,000 years (confidence was constructed by using the neighbor-joining algorithm (17). limits: 1,940,000 and 4,534,000 years). In this tree the Neandertal forms the outgroup to the modern Relative Divergence Between Neandertals and Humans. In human mtDNAs (Fig. 2). The reliability of the branch con- western Europe, Neandertals and modern humans coexisted necting the Neandertal mtDNA with that of the modern from approximately 40,000 years ago to less than 30,000 years humans was tested by the likelihood-mapping approach (18), ago (34). The implications of that coexistence in terms of where quartets of sequences involving the Neandertal, a culture and genetic relationships are a matter of debate. The chimpanzee or bonobo, and two humans were analyzed such results presented here indicate that the mtDNA gene pools of that the probability of sampling each human sequence at least these two hominid forms had diverged for a substantial time once was 0.96. For each quartet, the likelihood of each of the before they came into contact. To put the extent of genetic three possible tree topologies was calculated. In 100% of the differentiation that had resulted into perspective, a useful 1,898,505 quartets tested the most likely topology had the comparison may be the differentiation found today among Neandertal mtDNA as an outgroup to that of the humans. chimpanzees and bonobos. The number of differences between Furthermore, among the modern human mtDNAs, nine and the Neandertal and modern humans is 35.5 2.3, about half eight African sequences were found to branch off on the first that between chimpanzees and bonobos (75.7 4.6). Unfor- and the second branch after the Neandertal, respectively. tunately, HVRII sequences are not available for different These branches were supported by 91% and 92% of quartets, subspecies of chimpanzees. However, if the analysis is confined respectively. to 312 bp of HVRI, the average difference between modern Thus, the phylogenetic analysis shows that the line leading humans and the Neandertal is 25.6 2.2, whereas that among to the Neandertal mtDNA diverged before the most recent 19 bonobos is 17.7 8.5, among 10 central chimpanzees (Pan common ancestor of the modern human mtDNA gene pool troglodytes troglodytes) is 14.6 8.1, among 25 western chim- existed. Furthermore, as has been pointed out earlier (5, panzees (P. troglodytes verus) is 21.8 9.7, and among 108 29–31), the branching pattern among human mtDNAs sug- eastern chimpanzees (P. troglodytes schweinfurthii) is 7.9 3.0. gests an African origin of the modern human mtDNA gene The observed differences between the subspecies varies from pool. 19.7 2.9 between central and eastern chimpanzees and Dates of Divergences. For the estimation of the ages of 36.2 6.1 and 33.0 4.5 between western and central, and MRCAs of different groups of mtDNAs, the observed nucle- western and eastern chimpanzees, respectively. Thus, the otide differences were corrected for multiple substitutions by average observed difference between the Neandertal mtDNA using the Tamura–Nei algorithm (17). The resulting genetic and the mtDNA of modern humans exceeds that occurring distances and the estimated age of the modern human– within chimpanzee subspecies and within bonobos, but is less chimpanzee split of 4–5 million years (22, 23) were used to than what is found between two of three pairwise comparisons calculate the substitution rate of 0.94 10 7 substitutions per between currently recognized subspecies of chimpanzees. site per year per lineage with 5.92 10 8 and 1.38 10 7 as When the differences are corrected for multiple substitutions, the lower and upper confidence limits. These estimates are in reasonable agreement with previous rate estimations for the this general situation remains unchanged. However, mtDNA mtDNA control region (32, 33). Using these rates, the age of sequences from more Neandertal individuals are needed to the MRCA of the Neandertal and modern human mtDNAs obtain a better understanding of the extent of separation was estimated to be 465,000 years, with confidence limits of between the mtDNA gene pools of Neandertals and modern 317,000 and 741,000 years. This age is significantly older than humans. that of the MRCA of modern human mtDNAs, which, by the same procedure, was determined to be 163,000 years, with CONCLUSIONS 111,000 and 260,000 years as confidence limits. Finally, the age of the MRCA of the mtDNAs of the seven chimpanzees and The divergence of the Neandertal mtDNA from the line leading to the contemporary human mtDNA gene pool is almost 3-fold older than the deepest divergence among con- temporary human mtDNAs. The extent of sequence diver- gence exceeds that found within current chimpanzee subspe- cies. This shows that the Neandertal mtDNA and the human ancestral mtDNA gene pool have evolved as separate entities for a substantial period of time and gives no support to the notion that Neandertals should have contributed mtDNA to the modern human gene pool. We are indebted to F. G. Zehnder and H.-E. Joachim (Rheinisches Landesmuseum Bonn) for permission to remove samples, to I. Boschi and V. Pascali for unpublished human mtDNA sequences, to P. Gagneux and U. Gerloff for unpublished chimpanzee and bonobo mtDNA sequences, to C. Capelli, S. Meyer, K. Strimmer, L. Vigilant, A. von Haeseler, and W. Schartau for discussion and technical help, and to the Boehringer–Ingelheim Fonds and the Deutsche For- schungsgemeinschaft for financial support. 1. Stringer, C. & McKie, R. (1996) African Exodus (Random House, London). 2. Wolpoff, M. & Caspari, R. (1997) Race and Human Evolution (Simon & Schuster, New York). FIG. 2. A schematic phylogenetic tree of the Neandertal mtDNA 3. Schmitz, R. W., Pieper, P., Bonte, W. & Krainitzki, H. (1995) in and 663 modern human mtDNA lineages. Only the relevant branches Advances in Forensic Sciences, Forensic Odontology, eds. Jacob, B. are shown. The tree was rooted with seven chimpanzees and two & Bonte, W. (Koster, Berlin), Vol. 7, pp. 42–44. ¨ bonobos. Numbers on internal branches indicate quartet puzzling 4. Schmitz, R. W. (1996) Doctoral thesis (University of Cologne, support values (18). Germany).
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