Tracing an invasion: landbridges, refugia, and the phylogeography of the Neotropical rattlesnake (Serpentes: Viperidae: Crotalus durissus).

Abstract Pleistocene fragmentation of the Amazonian rainforest has been hypothesized to be a major cause of Neotropical speciation and diversity. However, the role and even the reality of Pleistocene forest refugia have attracted much scepticism. In Amazonia, previous phylogeographical studies have focused mostly on organisms found in the forests themselves, and generally found speciation events to have predated the Pleistocene. However, molecular studies of open-formation taxa found both north and south of the Amazonian forests, probably because of vicariance resulting from expansion of the rainforests, may provide novel insights into the age of continuous forest cover across the Amazon basin. Here, we analyse three mitochondrial genes to infer the phylogeography of one such trans-Amazonian vicariant, the Neotropical rattlesnake (Crotalus durissus), which occupies primarily seasonal formations from Mexico to Argentina, but avoids the rainforests of Central and tropical South America. The phylogeographical pattern is consistent with gradual dispersal along the Central American Isthmus, followed by more rapid dispersal into and across South America after the uplift of the Isthmus of Panama. Low sequence divergence between populations from north and south of the Amazon rainforest is consistent with mid-Pleistocene divergence, approximately 1.1 million years ago (Ma). This suggests that the Amazonian rainforests must have become fragmented or at least shrunk considerably during that period, lending support to the Pleistocene refugia theory as an important cause of distribution patterns, if not necessarily speciation, in Amazonian forest organisms. These results highlight the potential of nonforest species to contribute to an understanding of the history of the Amazonian rainforests themselves.

The early molecular response to imatinib predicts cytogenetic and clinical outcome in chronic myeloid leukaemia.

Real-time quantitative reverse transcription-polymerase chain reaction (Q-RT-PCR) is increasingly used to monitor responses in chronic myeloid leukaemia (CML). The peripheral blood BCR-ABL/ABL ratio, as assessed by Q-RT-PCR, has been shown to correlate with the contemporary cytogenetic response in patients receiving imatinib (Glivec, Gleevec). We have used Q-RT-PCR to monitor the early molecular response to 4 weeks and 3 months of imatinib therapy, in 47 patients with established CML. After 4 weeks of imatinib therapy, patients whose BCR-ABL/ABL ratio had fallen to less than 50% that of baseline had a significantly higher probability of achieving a major cytogenetic response after 6 months of therapy, when compared with those whose ratio did not fall by this amount (P < 0.001). Similarly, patients whose ratio at 3 months was less than 10% of that at baseline had a significantly higher probability of achieving a major cytogenetic remission at 6 months (P < 0.001). Patients who achieved these falls in their BCR-ABL/ABL ratio at either 4 weeks or 3 months had a superior progression-free survival at a median follow-up of 16.5 months (P = 0.01 and 0.003 respectively). These effects were independent of patient age and disease stage. The occurrence of peripheral blood cytopenias sufficiently severe to interrupt therapy was unrelated to progression-free survival. In conclusion, the data suggest that the early trend in the BCR-ABL/ABL ratio may be clinically useful for the early identification of patients destined to fare poorly on imatinib.

Serial monitoring of BCR-ABL by peripheral blood real-time polymerase chain reaction predicts the marrow cytogenetic response to imatinib mesylate in chronic myeloid leukaemia.

Imatinib mesylate (trade name Glivec or Gleevec) is emerging as an important therapy in the management of chronic myeloid leukaemia (CML). It is clinically useful to monitor the cytogenetic response to imatinib, although frequent marrow examinations are inconvenient. We have used serial real-time reverse transcription-polymerase chain reaction (RT-PCR) to monitor the ratio of peripheral blood BCR-ABL to normal ABL transcripts in 43 patients receiving imatinib, and compared the results to concurrent conventional bone marrow (BM) cytogenetics. After 6 months of treatment, 13 cases were complete cytogenetic responders, defined as all BM metaphases negative for the Philadelphia (Ph) chromosome. In these patients, the BCR-ABL/ABL ratio was less than 0.08%. Six cases achieved a partial cytogenetic response (1-35% Ph-positive BM metaphases) and their BCR-ABL/ABL ratio was between 0.08 and 10%. In total, 24 cases were cytogenetic non-responders, and their BCR-ABL/ABL ratio exceeded 11%. The data suggested that the 6-month BCR-ABL/ABL ratio may reliably predict the contemporary marrow cytogenetic response. It was concluded that serial real-time RT-PCR may offer a convenient surrogate assessment of the marrow cytogenetic response to imatinib therapy in CML.