Population structure and genetic variability of mainland and insular populations of the Neotropical water rat, Nectomys squamipes (Rodentia, Sigmodontinae)

Seven microsatellite loci were used to investigate the genetic variability and structure of six mainland and two island populations of the Neotropical water rat Nectomys squamipes, a South American semi-aquatic rodent species with a wide distribution. High levels of variability were found within mainland populations while island populations were less variable but the more differentiated in respect to allele number and frequency. The time of biological divergence between mainland and island populations coincided with geological data. A significant geographic structure was found in mainland populations (q = 0.099; r = 0.086) although the degree of differentiation was relatively low in respect to the distance between surveyed localities (24 to 740 km). Genetic and geographic distances were not positively correlated as previously found with random amplified polymorphic DNA (RAPD) markers. Significant but low genetic differentiation in the mainland and lack of isolation by distance can be explained by large population size and/or recent population expansion. Additionally, the agreement between the age of geologic events (sea level fluctuations) and divergence times for insular populations points to a good reference for molecular clock calibration to associate recent environmental changes and the distribution pattern of small mammals in the Brazilian Atlantic Forest

BRCA1 mutations in Brazilian patients

BRCA1 mutations are known to be responsible for the majority of hereditary breast and ovarian cancers in women with early onset and a family history of the disease. In this paper we present a mutational survey conducted in 47 Brazilian patients with breast/ovarian cancer, selected based on age at diagnosis, family history, tumor laterality, and presence of breast cancer in male patients. All 22 coding exons and intron-exon junctions were sequenced. Constitutional mutations were found in seven families, consisting of one insertion (insC5382) in exon 20 (four patients), one four base-pair deletion (3450-3453delCAAG) in exon 11 resulting in a premature stop codon (one patient), one transition (IVS17+2T> C) in intron 17 affecting a mRNA splicing site (one patient), and a C> T transition resulting in a stop-codon (Q1135X) in exon 11 (one patient). The identification of these mutations which are associated to hereditary breast and ovarian cancers will contribute to the characterization of the mutational spectrum of BRCA1 and to the improvement of genetic counseling for familial breast/ovarian cancer patients in Brazil.