New Canadian amber deposit fills gap in fossil record near end-Cretaceous mass extinction

Amber preserves an exceptional record of tiny, soft-bodied organisms and chemical environmental signatures, elucidating the evolution of arthropod lineages and the diversity, ecology, and biogeochemistry of ancient ecosystems. However, globally, fossiliferous amber deposits are rare in the latest Cretaceous and surrounding the Cretaceous-Paleogene (K-Pg) mass extinction.1,2,3,4,5 This faunal gap limits our understanding of arthropod diversity and survival across the extinction boundary.2,6 Contrasting hypotheses propose that arthropods were either relatively unaffected by the K-Pg extinction or experienced a steady decline in diversity before the extinction event followed by rapid diversification in the Cenozoic.2,6 These hypotheses are primarily based on arthropod feeding traces on fossil leaves and time-calibrated molecular phylogenies, not direct observation of the fossil record.2,7 Here, we report a diverse amber assemblage from the Late Cretaceous (67.04 ± 0.16 Ma) of the Big Muddy Badlands, Canada. The new deposit fills a critical 16-million-year gap in the arthropod fossil record spanning the K-Pg mass extinction. Seven arthropod orders and at least 11 insect families have been recovered, making the Big Muddy amber deposit the most diverse arthropod assemblage near the K-Pg extinction. Amber chemistry and stable isotopes suggest the amber was produced by coniferous (Cupressaceae) trees in a subtropical swamp near remnants of the Western Interior Seaway. The unexpected abundance of ants from extant families and the virtual absence of arthropods from common, exclusively Cretaceous families suggests that Big Muddy amber may represent a yet unsampled Late Cretaceous environment and provides evidence of a faunal transition before the end of the Cretaceous.

Relapse after bone marrow transplantation: evidence for distinct immunological mechanisms between adult and paediatric populations

Donor lymphocyte infusions are particularly effective for remission induction in malignant cells in patients who relapse after allogeneic progenitor cell transplantation (PCT) and who remain sensitive to the administration of unprimed donor T and/or natural killer (NK) cells present in donor lymphocyte infusions. To determine whether relapse after unmanipulated PCT could be ascribed to donor T and/or NK cell loss or tolerization, we evaluated the chimeric status of 81 patients with haematological malignancies who were receiving allogeneic unmanipulated PCT. The incidence of mixed chimaerism (MC) in unfractionated mononuclear leucocyte samples decreased rapidly after transplant, and was not detectable 4 months after PCT, even in patients who subsequently relapsed. The chimeric status of immune effector cell subsets was then evaluated in 15 patients at the time of relapse. All adults demonstrated complete donor haematopoiesis (CDH) for all cell lineages, whereas T- and NK-cell MC was only found in patients younger than age 13 years (P = 0.004). MC was not found in T nor NK cells of a control group consisting of age-matched paediatric patients in remission after allogeneic PCT. Thus, in adults, T and NK cell MC disappears early after unmanipulated allogeneic PCT and is absent at the time of relapse. However, the identification of donor T and NK cell loss in the paediatric relapsed but not remission patients suggests a distinct mechanism of relapse.

Nonrandom X-inactivation patterns in normal females: lyonization ratios vary with age

The utility of X-inactivation based clonality assays for evaluation of human neoplasia is well-documented. However, excessive Lyonization is a potential limitation of these assays, because it mimics clonal derivation of cells. The incidence of excessive Lyonization in healthy females is controversial, with reported incidence varying from 4% to 33%. Several explanations have been offered for the observed variation, including different criteria for excessive Lyonization, diversity of X-linked clonality assays, small population sizes and more recently, tissue specificity of X-inactivation patterns. However, it is also possible that stem cell depletion, clonal hematopoiesis, or selection pressures on blood cells results in an increased incidence of excessive skewing. If any of the latter is true, then the incidence of excessive skewing should increase with age in blood cells. To test this hypothesis, we determined X-inactivation ratios at the human androgen receptor locus of 295 normal females from three age groups: (1) neonates, (2) females 28 to 32 years old and, (3) females aged > or = 60 years. The incidence of skewing (allele ratios > or = 3:1) was 8.6% (14 of 162) in neonates (P = .104 v 28 to 32); 16.4% (11/67) in 28 to 32 y.o. (P = .0064 v > or = 60), and 37.9% (25 of 66) in women > or = 60 y.o. (P < .0001 v neonates). When a more stringent criterion for skewing was used (allele ratios > or = 10:1), the incidence was 1.9% (3 of 162) in neonates (P = .362 v 28 to 32), 4.5% (3 of 67) in 28 to 32 y.o. (P = .0022 v > or = 60), and 22.7% (15 of 66) in > or = 60 y.o. group (P < .0001 v neonates). Results have been confirmed at the phosphoglycerate kinase locus for 48 heterozygous females. The incidence of excessive skewing increases with age. In neonates, the incidence is low and may correspond to true excessive Lyonization. Acquired skewing occurs with aging in normal females and is present in 38% of females over the age of 60. Further studies are needed to determine whether acquired skewing is a consequence of stem cell depletion, true clonal hematopoiesis, growth advantage conferred by parental-specific X-chromosomes, or other causes. These data provide an explanation for variation in reported incidence of excessive skewing in normal females. Furthermore, these findings suggest that any study of clonality using X-inactivation based assays should incorporate age-matched controls for Lyonization.