Friday 25 July, 2014

Researchers map genetic code of New Zealand’s first settlers

Published On: Wed, Oct 24th, 2012 | Genomics | By BioNews

In a landmark study, University of Otago researchers have achieved the feat of sequencing complete mitochondrial genomes for members of what was likely to be one of the first groups of Polynesians to settle New Zealand and have revealed a surprising degree of genetic variation among these pioneering voyagers.

The Otago researchers’ breakthrough means that similar DNA detective work with samples from various modern and ancient Polynesian populations might now be able to clear up competing theories about the pathways of their great migration across the Pacific to New Zealand.

Coming home: Rangitane iwi tupuna reburial ceremony at Wairau Bar in 2009.

Results from the team’s successful mapping of complete mitochondrial genomes of four of the Rangitane iwi tupuna (ancestors) who were buried at a large village on Marlborough’s Wairau Bar more than 700 years ago will be published online in the prestigious US journal Proceedings of the National Academy of Sciences (PNAS).

Study director Professor Lisa Matisoo-Smith explains that mitochondrial DNA (mtDNA) is only inherited through the mother’s side and can be used to trace maternal lineages and provide insights into ancient origins and migration routes.

“We found that three of the four individuals had no recent maternal ancestor in common, indicating that these pioneers were not simply from one tight-knit kin group, but instead included families that were not directly maternally related. This gives a fascinating new glimpse into the social structure of the first New Zealanders and others taking part in the final phases of the great Polynesian migration across the Pacific.”

The researchers discovered that the four genomes shared two unique genetic markers found in modern Maori while also featuring several previously unidentified Polynesian genetic markers. Intriguingly, they also discovered that at least one of the settlers carried a genetic mutation associated with insulin resistance, which leads to Type 2 diabetes.

“Overall, our results indicate that there is likely to be significant mtDNA variation among New Zealand’s first settlers. However, a lack of genetic diversity has previously been characterised in modern-day Maori and this was thought to reflect uniformity in the founding population.

“It may be rather that later decimation caused by European diseases was an important factor, or perhaps there is actually still much more genetic variation today that remains to be discovered. Possibly, it may have been missed due to most previous work only focusing on a small portion of the mitochondrial genome rather than complete analyses like ours.”

Professor Matisoo-Smith and colleagues including ancient DNA analysis expert Dr Michael Knapp used Otago’s state-of-the-art ancient DNA research facilities to apply similar techniques that other scientists recently employed to sequence the Neanderthal genome.

“We are very excited to be the first researchers to successfully sequence complete mitochondrial genomes from ancient Polynesian samples. Until the advent of next generation sequencing techniques, the highly degraded state of DNA in human remains of this age has not allowed such genomes to be sequenced,” she says.

Now that the researchers have identified several unique genetic markers in New Zealand’s founding population, work can begin to obtain and sequence other ancient and modern DNA samples from Pacific islands and search for these same markers.

“If such research is successful, this may help identify the specific island homelands of the initial canoes that arrived in Aotearoa/New Zealand 700 years ago,” she says.

Reference:
Knapp M, Horsburgh KA, Prost S, Stanton JA, Buckley HR, Walter RK, Matisoo-Smith EA. Complete mitochondrial DNA genome sequences from the first New Zealanders. Proc Natl Acad Sci U S A. 2012 Oct 22. [Epub ahead of print] PubMed PMID: 23091021.

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