\NEW YORK – Northern and southern Italian populations began to diverge genetically thousands of years ago, according to a new study.
Researchers from the University of Bologna sequenced the genomes of more than three dozen unrelated individuals from northern and southern Italy and compared their genomes, not only to each other but also to the genomes of other populations, including ancient populations. The Italian population is thought to reflect on a smaller scale the biological and demographic processes that shaped the wider European population, the researchers noted.
Through their analysis, the researchers uncovered genetic differences between northern and southern Italian populations. While some of these differences reflect the varying influence of outside populations on Italians, they also revealed what appear to be specific biological adaptations to the two regions of Italy that influence obesity and melanoma susceptibility. These factors all combined to shape the Italian population, as the researchers reported on Thursday in BMC Biology.
"When comparing sequences between modern and ancient genome samples, we found early genetic divergence between the ancestors of northern and southern Italian groups dating back to the Late Glacial, around 19,000 to 12,000 years ago," lead author Marco Sazzini from the University of Bologna said in a statement. "Migrations during the Neolithic and Bronze Age periods, thousands of years later, then further differentiated their gene pools."
For their analysis, the researchers generated whole-genome sequencing data on 38 individuals from different regions of Italy whose families had lived there for generations. These individuals represented the extreme ends of the clines between the northern and southern Italian populations.
When they compared these two populations to other modern populations, the researchers found varying influences. Both Italian populations shared similar portions of their DNA with Sardinians and northern Caucasian populations. These two groups, the researchers noted, are thought to reflect the early Neolithic and Bronze Age contributions to the ancestral pan-European genetic background. At the same time, southern Italians shared about 30 percent of their DNA with Near Eastern populations, while northern Italians share little, if any DNA, with Near Eastern populations. Instead, northern Italians shared more of their genetic background with Eastern and Northern European groups and the Basque.
Similarly, after adding in previously published data from ancient individuals, the researchers found that southern Italians shared more genetic ancestry with Chalcolithic/Bronze Age and Neolithic individuals from Anatolia, Armenia, the Near East, and Greece, while northern Italians shared more genetic ancestry Western Europeans dating back to the Copper Age.
The researchers estimated that northern and southern Italians began to diverge thousands of years ago, during the late Glacial Maximum, noting that southern Italy has been proposed to have served as a refuge for people during that time.
Later, northern and southern Italians began to diverge further, and the researchers uncovered differing regions of the genome that are under positive or balancing selection in one population, but not the other.
In northern Italians, the researchers teased out a signal of selection involving the ADCY genes, which help regulate thermogenesis and adiposity as well as influence susceptibility to diabetes and obesity. The researchers speculate that this may have enabled northern Italians to adapt to lower environmental temperatures and high-calorie diets and could now account for the lower rate of diabetes seen in northern Italians, as compared to southern Italians.
Southern Italians, meanwhile, appeared to have a signal of selection affecting the mucin gene C1GALT1, which may represent an adaptation to microorganisms in region, and one affecting the FZD/Wnt genes involved in melanin production, which could account for the lower rate of melanoma now seen in southern Italians, as compared to northern Italians.
"Further research in this area may help us understand how the observed genetic differences can impact population health or predisposition to a number of diseases," Sazzini added.