Preliminary results of mitochondrial DNA sequence variation in Spanish Pyrenean populations

Article Outline

• Abstract
• 1. Introduction and aims
• 2. Materials and methods
• 3. Results and discussion
• Conflict of interest
• Role of funding
• Acknowledgements
• References
• Copyright

Abstract 

Mitochondrial DNA sequences of the two hypervariable regions HVS-I and HVS-II were determined for 233 unrelated autochthonous individuals from East, Central and West Pyrenees. Resulting haplogroups were confirmed with RFLPs. Although the distribution of mitochondrial DNA haplogroups in the Pyrenees presents differences between populations, the results obtained may well support the hypothesis that the mountain chain did not act as a barrier to gene flow among Pyrenean populations. These preliminary data could be helpful for the understanding of the present distribution of mitochondrial DNA haplogroups in Iberian Peninsula and its phylogeny.

Keywords: mtDNA, Pyrenean population, Haplogroups

Back to Article Outline

1. Introduction and aims 

The Pyrenees mountain range spans 430km from the Cantabric sea to the Mediterranean shore separating the Iberian Peninsula from the rest of the European mainland. The Pyrenees, are typically divided into three sections: the Atlantic or Western, the Central, and the Eastern. Orographical and geographical characteristics of the Pyrenees create numerous valleys favouring the isolation of small populations in which microevolutive processes determine their genetic structure. Such circumstances likely played a major role in shaping current genetic structure in present-day Pyrenean populations [1]. The main objective of this work was to obtain data from populations scattered throughout the entire Spanish area of the Pyrenees and to compare the results on these studied populations with those previously published in order to know the potential microgeographical differentiation of the Pyrenean populations.

Back to Article Outline

2. Materials and methods 

Blood samples were obtained from unrelated volunteer donors at central hospitals from the Pyrenees. Sample sizes and geographical locations (Fig. 1) were: 108 individuals from East Pyrenees; 68 individuals from Central Pyrenees and 57 individuals from West Pyrenees. All individuals had their four grandparents born in the region. Polymorphisms of the mitochondrial DNA HVRI and II were amplified in a duplex PCR using primers described in Gabriel and Calloway [2] and modified by Chong and Calloway [3]. Sequencing was carried out in an ABI310 Genetic Analyzer (Applied Biosystems). The obtained haplotypes were classified into haplogroups according to mutations between positions 16016 and 16394 for HVI and between positions 58 and 429 for HVII. The “mtDNAmanager” software was used to estimate the most probable mtDNA haplogroups [4]. Haplogroup assignments of H, U, Pre-V, V, K, Pre-HV and HV were confirmed by RFLPs described in Turchi [5].

• 
  • View Large Image
  • Download to PowerPoint

• Fig. 1. 

  Map of the Iberian Peninsula, with zoom in the Pyrenean region. West Pyrenees (W), Central Pyrenees (C) and East Pyrenees (E) are shown in the map.

Back to Article Outline

3. Results and discussion 

Sequence comparisons with rCRS allowed the identification of 131 different haplotypes considering both hypervariable regions (insertions in the HV2 poly-C stretch were ignored) in all samples. Only 15 haplotypes were presented in more than one population. Two haplotypes were shared in West, Central and East Pyrenees: 16298C-72C-263G-309.1C-315.1C and CRS-263G-309.1C-315-1C, these being the most frequent in all samples.

In all populations, the most frequent haplogroup was H, followed by haplogroups U and J, which showed different frequencies among populations (Table 1). Haplogroup U presented higher frequency in central and east Pyrenees (22.06% and 19.44%, respectively), whereas haplogroup J presented the most frequent in western Pyrenees (19.30%). Haplogroup V/HV0/HV0* was also present with a frequency that ranged between 8.77% and 14.81%. Other European haplogroups were also present in these populations: K, T, I, X and W.

Table 1. Frequency of haplogroups in Pyrenean populations.

The distribution of mitochondrial DNA haplogroups in West Pyrenees – characterized by high frequency for haplogroup J, K, V and U5 – may well support certain degree of continuity with Basque populations recently analyzed for the same mtDNA region by Alfonso-Sánchez and Cardoso [6], but the variability found about haplogroup J and V shows differences from initial studies of these populations related to the mitochondrial genome variability in the Basque region. The distribution of mitochondrial DNA haplogroups in Central Pyrenees shows a high frequency for haplogroups V and U5 and low frequency of haplogroups J and K respect to West and East Pyrenean. Respect to other Spanish and France [7] populations, in general Pyrenean populations present different frequencies for haplogroups J, V and U5. These results indicate that an old substrate is preponderant in populations of the whole Pyrenean fringe. Differences among Central, Western and East Pyrenees seem to indicate a differential gene flow across Pyrenean population.

Although the distribution of mitochondrial DNA haplogroups in Pyrenees, presents differences among populations, the results obtained may well support the hypothesis that the mountain chain did not act as a barrier to gene flow among Pyrenean populations. These preliminary data could be helpful for the understanding of the present distribution of mitochondrial DNA haplogroups in Iberian Peninsula.

Back to Article Outline

Conflict of interest 

None.

Back to Article Outline

Role of funding 

This work was financed by projects from Complutense University PR48/01-9837 and the Spanish Ministry of Science and Education CGL2006-07828/BOS.

Back to Article Outline

Acknowledgements 

The authors thank Lourdes Montsant (Hospital de Puigcerda), Carles Borrull and M^a Angeles Bordás (Hospital Vall D’Arán), Ferrán Gómez (Fundación Santo Hospital de La Seu d’Urgell), Isabel Maroto (Consorcio Hospitalario de Jaca), Rafael Eneterreaga and Javier González (Centros de Salud “Cinco Villas”).

Back to Article Outline

References 

1. López-Parra AM, Gusmão L, et al. In search of the pre- and post-neolithic genetic substrates in Iberia: evidence from Y-chromosome in Pyrenean populations. Ann. Hum. Genet. 2009;73(1):42–53
   • View In Article
   • CrossRef
2. Gabriel MN, Calloway CD, et al. Identification of human remains by immobilized sequence-specific oligonucleotide probe analysis of mtDNA hypervariable regions I and II. Croat. Med. J. 2003;44:293–298
   • View In Article
   • MEDLINE
3. Chong MD, Calloway CD, et al. Optimization of a duplex amplification and sequencing strategy for the HVI/HVII regions of human mitochondrial DNA for forensic casework. Forensic Sci. Int. 2005;154(2–3):137–148
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (785 KB)
   • CrossRef
4. Lee HY, Song I, Ha E, et al. mtDNAmanager: a Web-based tool for the management and quality analysis of mitochondrial DNA control-region sequences. BMC Bioinformatics. 2008;9:483
   • View In Article
   • CrossRef
5. Turchi C, Buscemi L, et al. Italian mitochondrial DNA database: results of a collaborative exercise and proficiency testing. Int. J. Legal Med. 2008;122:199–204
   • View In Article
   • CrossRef
6. Alfonso-Sánchez MA, Cardoso S, et al. Mitochondrial DNA haplogroup diversity in Basques: a reassessment base don HVI and HVII polymorphisms. Am. J. Hum. Biol. 2008;20(2):154–164
   • View In Article
   • CrossRef
7. Richard C, Pennarun E, et al. An mtDNA perspective of French genetic variation. Ann. Hum. Biol. 2007;34(1):68–79
   • View In Article
   • MEDLINE
   • CrossRef