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Rafael Montiel

Publications and source records attributed to Rafael Montiel.

5 recordsLinked to original sources
PubMed2006

The complete mitochondrial genome of the entomopathogenic nematode Steinernema carpocapsae: insights into nematode mitochondrial DNA evolution and phylogeny.

We determined the complete sequence of the mitochondrial DNA of the entomopathogenic nematode Steinernema carpocapsae and analyzed its structure and composition as well as the secondary structures predicted for its tRNAs and rRNAs. Almost the complete genome has been amplified in one fragment with long PCR and sequenced using a shotgun strategy. The 13,925-bp genome contains genes for 2 rRNAs, 22 tRNAs, and 12 proteins and lacks an ORF encoding ATPase subunit 8. Four initiation codons were inferred, TTT, TTA, ATA, and ATT, most of the genes ended with TAA or TAG, and only two had a T as an incomplete stop codon. All predicted tRNAs showed the nonconventional secondary structure typical of Secernentea. Although we were able to fold the sequences of trnN, trnD, and trnC into more conventional cloverleaf structures after adding adjacent nucleotides, northern blot experiments showed that the nonstandard tRNAs are actually expressed. Phylogenetic and comparative analyses showed that the mitochondrial genome of S. carpocapsae is more closely related to the genomes of A. suum and C. elegans than to that of Strongyloides stercoralis. This finding does not support the phylogeny based on nuclear small subunit ribosomal DNA sequences previously published. This discrepancy may result from differential reproductive strategies and/or differential selective pressure acting on nuclear and mitochondrial genes. The distinctive characteristics observed among mitochondrial genomes of Secernentea may have arisen to counteract the deleterious effects of Muller's ratchet, which is probably enhanced by the reproductive strategies and selective pressures referred to above.

Animals↗
PubMed2005

Understanding differences between phylogenetic and pedigree-derived mtDNA mutation rate: a model using families from the Azores Islands (Portugal).

We analyzed the control region of the mitochondrial DNA (mtDNA) from maternally related individuals originating from the Azores Islands (Portugal) in order to estimate the mutation rate of mtDNA and to gain insights into the process by which a new mutation arises and segregates into heteroplasmy. Length and/or point heteroplasmies were found at least in one individual of 72% of the studied families. Eleven new point substitutions were found, all of them in heteroplasmy, from which five appear to be somatic mutations and six can be considered germinal, evidencing the high frequency of somatic mutations in mtDNA in healthy young individuals. Different values of the mutation rate according to different assumptions were estimated. When considering all the germinal mutations, the value of the mutation rate obtained is one of the highest reported so far in family studies. However, when corrected for gender (assuming that the mutations present in men have the same evolutionary weight of somatic mutations because they will inevitably be lost) and for the probability of intraindividual fixation, the value for the mutation rate obtained for HVRI and HVRII (0.2415 mutations/site/Myr) was in the upper end of the values provided by phylogenetic estimations. These results indicate that the discrepancy, that has been reported previously, between the human mtDNA mutation rates observed along evolutionary timescales and the estimations obtained using family pedigrees can be minimized when corrections for gender proportions in newborn individuals and for the probability of intraindividual fixation are introduced. The analyses performed support the hypothesis that (1) in a constant, tight bottleneck genetic drift alone can explain different patterns of heteroplasmy segregation and (2) in neutral conditions, the destiny of a new mutation is strictly related to the initial proportion of the new variant. Another important point arising from the data obtained is that, even in the absence of a paternal contribution of mtDNA, recombination may occur between mtDNA molecules present in an individual, which is only observable if it occurs between mtDNA types that differ at two or more positions.

Azores↗
PubMed2005

Peopling of the Azores Islands (Portugal): data from the Y chromosome.

Nine Atlantic islands with approximately five and a half centuries of demographic history constitute the Portuguese archipelago of the Azores. Despite the recent peopling history of these islands, written records regarding the specific origin and relative proportions of the first settlers are scarce and incomplete. To gain insights into the history of the peopling of the Azores and to evaluate to what extent population imports described in historical sources left their marks on the genetic constitution of the present-day populations, we analyzed 11 Y-chromosome biallelic markers in a sample of 145 unrelated individuals of Azorean ancestry. The main results of this study indicate that the genetic profile of the Azorean male population shows high affinities with that of mainland Portugal, in accordance with the general knowledge, derived from historical sources, that the Portuguese were the major contributors to the Azorean founding population. Nevertheless, genetic traces of settlers from other origins also mentioned in historical records can still be found in the present-day population. Thus typically sub-Saharan male lineages were detected in the archipelago, in contrast to what has been described for mainland Portugal. Furthermore, compared to what has been described for the mainland Portugal population, our data support a stronger influence of people of Jewish origin, as detected by an increased frequency of lineages belonging to haplogroup J.

Azores↗
PubMed2004

Determination of human caucasian mitochondrial DNA haplogroups by means of a hierarchical approach.

In this paper we propose a hierarchical approach that allows the screening of mitochondrial DNA (mtDNA) haplogroups in populations that have essentially West Eurasian mtDNA backgrounds but that could have some non-West Eurasian contributions. To develop and validate this scheme, we used data on 18 coding region polymorphisms (17 analyzed by RFLP analysis and 1 by sequencing) and sequences of hypervariable segment I (HVSI) of the mtDNA control region from the Azores Islands (Portugal) population. The proposed scheme allows the characterization of almost all West Eurasian and African major clusters by means of RFLPs. Furthermore, the scheme includes information on situations in which sequencing is pertinent to defining a particular haplogroup. The validity of the scheme is ensured by (1) using relatively stable polymorphic positions, (2) screening more than one position to define a specific haplogroup, and (3) typing confirmatory positions. Dubious samples can be resolved by sequencing. The robustness of this approach was assessed by sequencing all samples for HVSI, taking advantage of the previously established relationships between RFLPs and control region sequence polymorphisms. The use of this hierarchical approach avoids the screening of unnecessary control region polymorphisms and therefore results in a more rapid and cost-efficient screening than one in which all polymorphic positions are analyzed. Even if this approach leads to a lower level of phylogeographic resolution than the sequencing of all samples, it allows us to define population movements on a continental level and can be applied, unlike sequencing all samples, with a low cost in any laboratory.

Azores↗