Loss of heterozygosity in hypotriploid cell cultures from testicular tumours

Summary We have established cell lines with a hypotriploid chromosome number from four testicular tumours. Each line had at least one Y chromosome and most of the informative centromere and enzyme markers were heterozygous implying that the tumours originated from germ cells before the first meiotic division. The small metacentric marker chromosome (i12p), specific for testicular tumours, was present in all tumour cell lines and up to three copies were found in some lines. Rearrangements of chromosome 1 and 11 were each found in three out of four tumours. The rearrangements of chromosome 1 all resulted in duplication of 1q and deletion of short-arm material from the same chromosome giving loss of heterozygosity for enzyme markers on 1p. Loss of satellite material from chromosome 13 and the centromere region of chromosome 9 were found in single cases. This study shows that even where the chromosome number of tumour cells is near triploid, regions of the genome can be deleted. The chromosomes most frequently involved in rearrangements, 1, 11, and 12 all contain sites of ras oncogenes and it is suggested that loss of normal alleles could result in homozygosity for mutant oncogenes which may play a part in tumour progression.     

Asymmetric response of forest and grassy biomes to climate variability across the African Humid Period: influenced by anthropogenic disturbance?

A comprehensive understanding of the relationship between land cover, climate change and disturbance dynamics is needed to inform scenarios of vegetation change on the African continent. Although significant advances have been made, large uncertainties exist in projections of future biodiversity and ecosystem change for the world's largest tropical landmass. To better illustrate the effects of climate–disturbance–ecosystem interactions on continental-scale vegetation change, we apply a novel statistical multivariate envelope approach to subfossil pollen data and climate model outputs (TraCE-21ka). We target paleoenvironmental records across continental Africa, from the African Humid Period (AHP: ca 14 700–5500 yr BP) – an interval of spatially and temporally variable hydroclimatic conditions – until recent times, to improve our understanding of overarching vegetation trends and to compare changes between forest and grassy biomes (savanna and grassland). Our results suggest that although climate variability was the dominant driver of change, forest and grassy biomes responded asymmetrically: 1) the climatic envelope of grassy biomes expanded, or persisted in increasingly diverse climatic conditions, during the second half of the AHP whilst that of forest did not; 2) forest retreat occurred much more slowly during the mid to late Holocene compared to the early AHP forest expansion; and 3) as forest and grassy biomes diverged during the second half of the AHP, their ecological relationship (envelope overlap) fundamentally changed. Based on these asymmetries and associated changes in human land use, we propose and discuss three hypotheses about the influence of anthropogenic disturbance on continental-scale vegetation change.