Pleistocene Homo sapiens from Middle Awash,Ethiopia

The origin of anatomically modern Homo sapiens and the fate of Neanderthals have been fundamental questions in human evolutionary studies for over a century. A key barrier to the resolution of these questions has been the lack of substantial and accurately dated African hominid fossils from between 100,000 and 300,000 years ago. Here we describe fossilized hominid crania from Herto, Middle Awash, Ethiopia, that fill this gap and provide crucial evidence on the location, timing and contextual circumstances of the emergence of Homo sapiens. Radioisotopically dated to between 160,000 and 154,000 years ago, these new fossils predate classic Neanderthals and lack their derived features. The Herto hominids are morphologically and chronologically intermediate between archaic African fossils and later anatomically modern Late Pleistocene humans. They therefore represent the probable immediate ancestors of anatomically modern humans. Their anatomy and antiquity constitute strong evidence of modern-human emergence in Africa.     

Wet and dry deposition of Chernobyl releases

The passage of the Chernobyl plume over the United Kingdom in May 1986 led to the deposition of radionuclides on the ground by wet and dry deposition processes. Here we analyse rainfall during the passage of the plume and the published monitoring data obtained afterwards, and show that levels of deposited 137Cs can be closely related to rainfall intercepting the plume. 137Cs was present in the atmosphere mostly as particulate species with wet deposition mechanisms dominating. In contrast, 131I was present as particulate and vapour phase material, and reported levels on grass and in cow's milk show that both wet and dry deposition mechanisms were important. 131I on grass and in cow's milk therefore shows a different geographic pattern to 137Cs, and is not so closely related to rainfall. We have calculated washout factors for locations where there are data on deposition, rainfall and air concentrations during the passage of the Chernobyl plume. From these factors and interpolated concentrations in the atmosphere, the total deposition of 137Cs has been estimated at each of 4,000 rain gauge stations in the United Kingdom. The results are presented as deposition contours and have been compared with measurements in parts of the country. Estimates of the total deposition of 131I and 137Cs show that less than or equal to 1% of the estimated total releases from Chernobyl were deposited on the United Kingdom.     

Cytotoxic T lymphocyte mediated lysis without release of serine esterase

Cloned cytotoxic T lymphocytes (CTL) can lyse target cells in a Ca2+-dependent or Ca2+-independent fashion, depending on the target cell used. We have used these Ca2+-free assay conditions to determine whether there is serine esterase release in the absence of extracellular Ca2+. We find that under conditions where there is significant target cell killing in the absence of Ca2+, there is no detectable serine esterase release. To the extent that serine esterase and perforin-like molecules reside in the same granules, these results also suggest that target cell killing may occur in the absence of degranulation. Our results provide an example of target cell killing without serine esterase release, and the first indication that lysis and degranulation can be functionally dissociated.     

Alteration of the quality of milk by expression of sheep beta-lactoglobulin in transgenic mice

Milk contains a large amount of protein, most of which consists of a few major species synthesized in the mammary gland. The genes encoding these proteins are single-copy, and expressed during pregnancy and lactation. Although beta-lactoglobulin (BLG) is the major protein in the whey of ruminants, it is not present in rodent milk. We have generated transgenic mice carrying the sheep BLG gene, and show that in such mice, BLG is specifically and abundantly expressed in the mammary gland during lactation. This results in a remarkable alteration of milk composition. These findings suggest that the manipulation of milk composition by gene transfer has considerable potential for the improvement of dairy animals.     

A Middle Jurassic 'sphenosuchian' from China and the origin of the crocodylian skull

The skull of living crocodylians is highly solidified and the jaw closing muscles are enlarged, allowing for prey capture by prolonged crushing between the jaws. Living species are all semi-aquatic, with sprawling limbs and a broad body that moves mainly from side-to-side; however, fossils indicate that they evolved from terrestrial forms. The most cursorial of these fossils are small, gracile forms often grouped together as the Sphenosuchia, with fully erect, slender limbs; their relationships, however, are poorly understood. A new crocodylomorph from deposits in northwestern China of the poorly known Middle Jurassic epoch possesses a skull with several adaptations typical of living crocodylians. Postcranially it is similar to sphenosuchians but with even greater adaptations for cursoriality in the forelimb. Here we show, through phylogenetic analysis, that it is the closest relative of the large group Crocodyliformes, including living crocodylians. Thus, important features of the modern crocodylian skull evolved during a phase when the postcranial skeleton was evolving towards greater cursoriality, rather than towards their current semi-aquatic habitus.     

Shotgun sequence assembly and recent segmental duplications within the human genome

Complex eukaryotic genomes are now being sequenced at an accelerated pace primarily using whole-genome shotgun (WGS) sequence assembly approaches. WGS assembly was initially criticized because of its perceived inability to resolve repeat structures within genomes. Here, we quantify the effect of WGS sequence assembly on large, highly similar repeats by comparison of the segmental duplication content of two different human genome assemblies. Our analysis shows that large (> 15 kilobases) and highly identical (> 97%) duplications are not adequately resolved by WGS assembly. This leads to significant reduction in genome length and the loss of genes embedded within duplications. Comparable analyses of mouse genome assemblies confirm that strict WGS sequence assembly will oversimplify our understanding of mammalian genome structure and evolution; a hybrid strategy using a targeted clone-by-clone approach to resolve duplications is proposed.