What caused extinction of the Pleistocene megafauna of Sahul?

During the Pleistocene, Australia and New Guinea supported a rich assemblage of large vertebrates. Why these animals disappeared has been debated for more than a century and remains controversial. Previous synthetic reviews of this problem have typically focused heavily on particular types of evidence, such as the dating of extinction and human arrival, and have frequently ignored uncertainties and biases that can lead to misinterpretation of this evidence. Here, we review diverse evidence bearing on this issue and conclude that, although many knowledge gaps remain, multiple independent lines of evidence point to direct human impact as the most likely cause of extinction.

Generativity, hierarchical action and recursion in the technology of the Acheulean to Middle Palaeolithic transition: a perspective from Patpara, the Son Valley, India.

The Acheulean to Middle Palaeolithic transition is one of the most important technological changes that occurs over the course of human evolution. Here we examine stone artefact assemblages from Patpara and two other excavated sites in the Middle Son Valley, India, which show a mosaic of attributes associated with Acheulean and Middle Palaeolithic industries. The bifaces from these sites are very refined and generally small, but also highly variable in size. A strong relationship between flake scar density and biface size indicates extensive differential resharpening. There are relatively low proportions of bifaces at these sites, with more emphasis on small flake tools struck from recurrent Levallois cores. The eventual demise of large bifaces may be attributed to the curation of small prepared cores from which sharper, or more task-specific flakes were struck. Levallois technology appears to have arisen out of adapting aspects of handaxe knapping, including shaping of surfaces, the utilization of two inter-dependent surfaces, and the striking of invasive thinning flakes. The generativity, hierarchical organization of action, and recursion evident in recurrent Levallois technology may be attributed to improvements in working memory.

Characterization of DRP2, a novel human dystrophin homologue.

The currently recognised dystrophin protein family comprises the archetype, dystrophin, its close relative, utrophin or dystrophin-related protein (DRP), and a distantly related protein known as the 87K tyrosine kinase substrate. During the course of a phylogenetic study of sequences encoding the characteristic C-terminal domains of dystrophin-related proteins, we identified an unexpected novel class of vertebrate dystrophin-related sequences. We term this class dystrophin-related protein 2 (DRP2), and suggest that utrophin/DRP be renamed DRP1 to simplify future nomenclature. DRP2 is a relatively small protein, encoded in man by a 45 kb gene localized to Xq22. It is expressed principally in the brain and spinal cord, and is similar in overall structure to the Dp116 dystrophin isoform. The discovery of a novel relative of dystrophin substantially broadens the scope for study of this interesting group of proteins and their associated glycoprotein complexes.

Further evidence for small-bodied hominins from the Late Pleistocene of Flores, Indonesia.

Homo floresiensis was recovered from Late Pleistocene deposits on the island of Flores in eastern Indonesia, but has the stature, limb proportions and endocranial volume of African Pliocene Australopithecus. The holotype of the species (LB1), excavated in 2003 from Liang Bua, consisted of a partial skeleton minus the arms. Here we describe additional H. floresiensis remains excavated from the cave in 2004. These include arm bones belonging to the holotype skeleton, a second adult mandible, and postcranial material from other individuals. We can now reconstruct the body proportions of H. floresiensis with some certainty. The finds further demonstrate that LB1 is not just an aberrant or pathological individual, but is representative of a long-term population that was present during the interval 95-74 to 12 thousand years ago. The excavation also yielded more evidence for the depositional history of the cave and for the behavioural capabilities of H. floresiensis, including the butchery of Stegodon and use of fire.

Archaeology and age of a new hominin from Flores in eastern Indonesia.

Excavations at Liang Bua, a large limestone cave on the island of Flores in eastern Indonesia, have yielded evidence for a population of tiny hominins, sufficiently distinct anatomically to be assigned to a new species, Homo floresiensis. The finds comprise the cranial and some post-cranial remains of one individual, as well as a premolar from another individual in older deposits. Here we describe their context, implications and the remaining archaeological uncertainties. Dating by radiocarbon (14C), luminescence, uranium-series and electron spin resonance (ESR) methods indicates that H. floresiensis existed from before 38,000 years ago (kyr) until at least 18 kyr. Associated deposits contain stone artefacts and animal remains, including Komodo dragon and an endemic, dwarfed species of Stegodon. H. floresiensis originated from an early dispersal of Homo erectus (including specimens referred to as Homo ergaster and Homo georgicus) that reached Flores, and then survived on this island refuge until relatively recently. It overlapped significantly in time with Homo sapiens in the region, but we do not know if or how the two species interacted.

The evolving landscape and climate of western Flores: an environmental context for the archaeological site of Liang Bua.

The rapidly changing landscape of the eastern Indonesian archipelago has evolved at a pace dictated by its tropical climate and its geological and tectonic history. This has produced accelerated karstification, flights of alluvial terraces, and complex, multi-level cave systems. These cave systems sometimes contain a wealth of archaeological evidence, such as the almost complete skeleton of Homo floresiensis found at the site of Liang Bua in western Flores, but this information can only be understood in the context of the geomorphic history of the cave, and the more general geological, tectonic, and environmental histories of the river valley and region. Thus, a reconstruction of the landscape history of the Wae Racang valley using speleothems, geological structure, tectonic uplift, karst, cave, and terrace development, provides the necessary evidence to determine the formation, age, evolution, and influences on the site. This evidence suggests that Liang Bua was formed as two subterranean chambers approximately 600ka, but could not be occupied until approximately 190ka when the Wae Racang wandered to the southern side of the valley, exposing the chamber and depositing alluvial deposits containing artifacts. During the next approximately 190k.yr., the chambers coalesced and evolved into a multi-level and interconnected cave that was subjected to channel erosion and pooling events by the development of sinkholes. The domed morphology of the front chamber accumulated deep sediments containing well stratified archaeological and faunal remains, but ponded water in the chamber further prevented hominin use of the cave until approximately 100ka. These chambers were periodically influenced by river inundation and volcanic activity, whereas the area outside the cave was greatly influenced by glacial phases, which changed humid forest environments into grassland environments. This combined evidence has important implications for the archaeological interpretation of the site.

Reconstructing the geomorphic history of Liang Bua, Flores, Indonesia: a stratigraphic interpretation of the occupational environment.

Liang Bua, in Flores, Indonesia, was formed as a subterranean chamber over 600ka. From this time to the present, a series of geomorphic events influenced the structure of the cave and cave deposits, creating a complex stratigraphy. Within these deposits, nine main sedimentary units have been identified. The stratigraphic relationships between these units provide the evidence needed to reconstruct the geomorphic history of the cave. This history was dominated by water action, including slope wash processes, channel formation, pooling of water, and flowstone precipitation, which created waterfalls, cut-and-fill stratigraphy, large pools of water, and extensive flowstone cappings. The reconstructed sequence of events over the last 190k.yr. has been summarized by a series of time slices that demonstrate the nature of the occupational environment in Liang Bua. The earliest artifacts at the site, dated to approximately 190ka, testify to hominin presence in the area, but the reconstructions suggest that occupation of the cave itself may not have been possible until after approximately 100ka. At approximately 95ka, channel erosion of a basal unit, which displays evidence of deposition in a pond environment, created a greater relief on the cave floor, and formed remanent areas of higher ground that later became a focus for hominin occupation from 74-61ka by the west wall and in the center of the cave, and from approximately 18-17ka by the east wall. These zones have been identified according to the sloping nature of the stratigraphy and the distribution of artifacts, and their locations have implications for the archaeological interpretation of the site.

Geochronology of cave deposits at Liang Bua and of adjacent river terraces in the Wae Racang valley, western Flores, Indonesia: a synthesis of age estimates for the type locality of Homo floresiensis.

A robust timeframe for the extant cave deposits at Liang Bua, and for the river terraces in the adjoining Wae Racang valley, is essential to constrain the period of existence and time of extinction of Homo floresiensis and other biota that have been excavated at this hominin type locality. Reliable age control is also required for the variety of artifacts excavated from these deposits, and to assist in environmental reconstructions for this river valley and for the region more broadly. In this paper, we summarize the available geochronological information for Liang Bua and its immediate environs, obtained using seven numerical-age methods: radiocarbon, thermoluminescence, optically- and infrared-stimulated luminescence (collectively known as optical dating), uranium-series, electron spin resonance, and coupled electron spin resonance/uranium-series. We synthesize the large number of numerical age determinations reported previously and present additional age estimates germane to questions of hominin evolution and extinction.

New ages for the last Australian megafauna: continent-wide extinction about 46,000 years ago.

All Australian land mammals, reptiles, and birds weighing more than 100 kilograms, and six of the seven genera with a body mass of 45 to 100 kilograms, perished in the late Quaternary. The timing and causes of these extinctions remain uncertain. We report burial ages for megafauna from 28 sites and infer extinction across the continent around 46,400 years ago (95% confidence interval, 51,200 to 39,800 years ago). Our results rule out extreme aridity at the Last Glacial Maximum as the cause of extinction, but not other climatic impacts; a "blitzkrieg" model of human-induced extinction; or an extended period of anthropogenic ecosystem disruption.

Stereological estimates of dopaminergic, GABAergic and glutamatergic neurons in the ventral tegmental area, substantia nigra and retrorubral field in the rat.

Midbrain dopamine neurons in the ventral tegmental area, substantia nigra and retrorubral field play key roles in reward processing, learning and memory, and movement. Within these midbrain regions and admixed with the dopamine neurons, are also substantial populations of GABAergic neurons that regulate dopamine neuron activity and have projection targets similar to those of dopamine neurons. Additionally, there is a small group of putative glutamatergic neurons within the ventral tegmental area whose function remains unclear. Although dopamine neurons have been intensively studied and quantified, there is little quantitative information regarding the GABAergic and glutamatergic neurons. We therefore used unbiased stereological methods to estimate the number of dopaminergic, GABAergic and glutamatergic cells in these regions in the rat. Neurons were identified using a combination of immunohistochemistry (tyrosine hydroxylase) and in situ hybridization (glutamic acid decarboxylase mRNA and vesicular glutamate transporter 2 mRNA). In substantia nigra pars compacta 29% of cells were glutamic acid decarboxylase mRNA-positive, 58% in the retrorubral field and 35% in the ventral tegmental area. There were further differences in the relative sizes of the GABAergic populations in subnuclei of the ventral tegmental area. Thus, glutamic acid decarboxylase mRNA-positive neurons represented 12% of cells in the interfascicular nucleus, 30% in the parabrachial nucleus, and 45% in the parainterfascicular nucleus. Vesicular glutamate transporter 2 mRNA-positive neurons were present in the ventral tegmental area, but not substantia nigra or retrorubral field. They were mainly confined to the rostro-medial region of the ventral tegmental area, and represented approximately 2-3% of the total neurons counted ( approximately 1600 cells). These results demonstrate that GABAergic and glutamatergic neurons represent large proportions of the neurons in what are traditionally considered as dopamine nuclei and that there are considerable heterogeneities in the proportions of cell types in the different dopaminergic midbrain regions.

Age-dependent and -independent behavioral deficits in Tg2576 mice.

The Tg2576 mouse model of excessive cerebral beta-amyloid deposition is now more than a decade old, yet consensus as to its exact characteristics and utility as a model of Alzheimer's disease is still lacking. Four different cohorts of control and Tg2576 mice, aged approximately 3, 9, 13 and 21 months, were therefore subjected to a battery of tests, principally to assess cognitive and species-typical behaviors. A novel test, the paddling Y-maze, demonstrated an age-dependent deficit in 10 and 14, but not 3 month Tg2576 mice, also in aged (21 month) control mice. However, in many other cognitive tests few Tg2576-related deficits could be shown. This frequently seemed attributable to poor performance of control mice. Tests of species-typical behaviors showed that Tg2576 mice had a deficit in burrowing behavior at all ages. An age-independent deficit was also seen in nest construction, but only when mice were group-housed; most individually housed mice in either group made reasonable nests. Overall, the results suggested that these Tg2576 mice are not a simple, suitable or reliable model for routine screening of treatments for Alzheimer's disease. However, this model might perform better behaviorally on a different genetic background.

Bipartite interaction between neurofibromatosis type I protein (neurofibromin) and syndecan transmembrane heparan sulfate proteoglycans.

The neurofibromatosis type 1 (NF1) gene encodes a large tumor suppressor protein (neurofibromin). Although it is known to possess Ras GTPase-activating protein (GAP) activity, the cellular role of neurofibromin remains unclear. Here we used yeast two-hybrid screening to identify neurofibromin-interacting proteins. Syndecan-2, a transmembrane heparan sulfate proteoglycan (HSPG), was isolated as a binding partner for two distinct regions of the neurofibromin protein. We subsequently found that neurofibromin can bind all four mammalian syndecans. NF1 interaction requires the transmembrane domain and a membrane-proximal region of the cytoplasmic tail of syndecan, but not the C terminus of syndecan known to bind to CASK, a membrane-associated guanylate kinase (MAGUK). Neurofibromin, syndecans, and CASK have overlapping subcellular distributions in axons and synapses of neurons, as shown by biochemical fractionation and immunostaining. Moreover, neurofibromin exists in a complex with syndecan and CASK in vivo, as evidenced by their coimmunoprecipitation from rat brain. Our findings suggest that interaction with different members of the syndecan family may be a mechanism for localizing neurofibromin to specialized domains of the plasma membrane.

Expression of the dystrophin-related protein 2 (Drp2) transcript in the mouse.

We have recently characterised a new member of the dystrophin gene family, DRP2, and its murine counterpart, Drp2, which encode dystrophin-related protein 2 (DRP2). DRP2 is predicted to resemble certain short C-terminal isoforms of dystrophin and dystrophin-related protein 1 (DRP1 or utrophin). We describe here a comprehensive survey of Drp2 expression in the mouse by RT-PCR, and compare the expression profile of Drp2 with that of the related genes Dmd, Drp1 and Dag1 that encode all the known isoforms of dystrophin, DRP1/utrophin and a component of the dystrophin-associated protein complex, dystroglycan, respectively. Drp2 was shown to be expressed throughout the central nervous system (CNS) and in several peripheral tissues including the eye, kidney, teeth, oesophagus, colon, epididymis and ovary. The expression of Drp2 in the CNS was then further defined by in situ hybridization. Overall, the pattern of Drp2 expression corresponds to a subset of the brain regions known to express Dag1, and shows substantial overlap with regions that express various isoforms of dystrophin (particularly in the cerebral cortex, hippocampus and cerebellum). These data define the distribution of Drp2 expression in the mouse, and raise the possibility that in the CNS it may be an important component in neuronal dystrophin-associated complexes.

Two novel members of the interleukin-1 receptor gene family, one deleted in Xp22.1-Xp21.3 mental retardation.

X-linked mental retardation is estimated to affect approximately 1 in 600 males. Although numerous genes responsible for syndromic mental retardation have been identified, the study of non-syndromic mental retardation suffers from intrinsic issues of genetic heterogeneity. During the investigation of three brothers with a contiguous gene deletion syndrome of Becker muscular dystrophy, glycerol kinase deficiency, congenital adrenal hypoplasia, and mental retardation, we found their dystrophin gene to be fused tail-to-tail with a gene encoding a novel member of the interleukin-1 receptor family, IL1RAPL1. This gene has a close relative in Xq22, which we call IL1RAPL2. Both IL1RAPL1 and IL1RAPL2 have novel C-terminal sequences not present in other related proteins, and are encoded by very large genes. The 1.8-megabase deletion in these patients removes not only the last exon of the dystrophin gene, the entire glycerol kinase and DAX-1 genes, and the MAGE-B gene cluster, but also three exons encoding the intracellular signalling domain of IL1RAPL1. The literature contains multiple reports of patients with non-syndromic mental retardation in association with an Xp22.1-Xp21.3 microdeletion of a marker which lies within the IL1RAPL1 gene. The gene is also wholly or partially deleted in patients with mental retardation as part of a contiguous deletion syndrome. We suggest that IL1RAPL1, and perhaps IL1RAPL2, are strong candidates for X-linked non-syndromic mental retardation loci, and that molecules resembling IL-1 and IL-18 play a role in the development or function of the central nervous system.

Conservation of components of the dystrophin complex in Drosophila.

Defects in the dystrophin complex (DC) underlie several human genetic disorders, but our dissection of its function is complicated by potential redundancy of the multiple vertebrate isoforms of most DC components. We here complete our previous description of Drosophila dystrophin, and show that the fly retains all essential components of the DC, but with substantially less diversity. Seventeen known human components (three dystrophin-related proteins, two dystrobrevins, five sarcoglycans, five syntrophins, one dystroglycan and one sarcospan) appear to be reduced to eight in Drosophila (one, one, three, two, one and none, respectively). The simplicity of this system recommends it as a model for its human counterpart.

Overexpressed human survival motor neurone isoforms, SMNDeltaexon7 and SMN+exon7, both form intranuclear gems but differ in cytoplasmic distribution.

Homozygous mutations of the telomeric survival motor neurone gene (SMN1) cause spinal muscular atrophy (SMA). The centromeric copy gene (SMN2) generally skips exon 7 during splicing and fails to compensate for SMN1 deficits, so SMA cells have reduced SMN protein and few nuclear gems. To investigate the role of exon 7 in SMN localisation, cDNAs for full-length SMN and SMNDeltaexon 7 were overexpressed in COS cells, neurones and SMA fibroblasts. Both constructs formed discrete intranuclear bodies colocalising with p80-coilin, but produced more cytoplasmic aggregates in cells overexpressing exon 7. Hence, the exon 7 domain enhances SMN aggregation but is not critical for gem formation.

Prostate cancer screening and beliefs about treatment efficacy: a national survey of primary care physicians and urologists.

PURPOSE: To describe practice patterns and beliefs of primary care physicians and urologists regarding early detection and treatment of prostate cancer. SUBJECTS AND METHODS: National probability samples of primary care physicians (n=444) and urologists (n=394) completed mail survey instruments in 1995. Physicians were asked about their use of prostate-specific antigen (PSA) testing for men of different ages and their beliefs about the value of radical prostatectomy, external-beam radiation therapy, and watchful waiting for men with differing life expectancies. RESULTS: Most primary care physicians report doing PSA tests during routine examination of men older than 50 years of age. The majority say they continue to do them on patients over 80 years and to refer men with abnormal values for biopsy. In contrast, only a minority of urologists would recommend PSA tests or biopsy for abnormal values for men over 75 years of age. More than 80% of primary care physicians and urologists doubt the value of radical prostatectomy for men with < 10 years of life expectancy; more primary care physicians than urologists see probable survival benefit in radiation therapy for patients with life expectancy < 10 years (48% versus 36%) or > 10 years (67% versus 53%). Thirteen percent of primary care physicians and only 3% of urologists consider watchful waiting to be as appropriate as aggressive therapy for men with > 10 years of life expectancy. CONCLUSIONS: Primary care physicians are more aggressive about PSA testing and referral for biopsy than most urologists recommend. Both groups recommend PSA testing and believe that aggressive treatment is more beneficial than existing evidence indicates.

Protein truncation test (PTT) to rapidly screen the DMD gene for translation terminating mutations.

We have developed a rapid and sensitive method to screen the Duchenne muscular dystrophy (DMD) mRNA for translation terminating mutations by a combination of RT-PCR (Reverse Transcription and Polymerase Chain Reaction) and in vitro transcription/translation applied to white blood cell mRNA. This technique was termed the protein truncation test (PTT). Here we demonstrate the detection of a point mutation in a DMD patient and his mother, a carrier. The PTT can also be used for carrier detection when no patient material is available, or in the case of spontaneous mutations. We developed a protocol to screen the total coding region of the DMD gene in 5-10 PTT reactions. Furthermore, PTT could be of diagnostic value in any disease where premature terminations form a substantial part of the total mutation spectrum.

Nicotinic acetylcholine receptors on capsaicin-sensitive nerves.

To study the density of nicotinic acetylcholine receptors on primary afferents and central nociceptive pathways, [3H](-)-nicotine binding was conducted in the cerebral cortex and spinal cord including dorsal roots and ganglia (DRG), of control rats and rats desensitized by neonatal capsaicin treatment. [3H](-)-nicotine binding in capsaicin-treated rats was reduced in cerebral cortex by 35% and spinal cord+DRG by 46% (p < 0.05). Functionally, both iontophoretically applied acetylcholine- and capsaicin-evoked flares (measured by laser Doppler flowmetry) were reduced in capsaicin-treated animals (p < 0.05); similarly, electrical stimulation-evoked flares were significantly lower in the same group, compared with controls (p < 0.05). These data provide direct evidence that many neuronal nicotinic acetylcholine receptors are associated with capsaicin-sensitive peptidergic neurones, including primary afferents, DRG and central nociceptive pathways.

Denervation impairs cutaneous microvascular function and blister healing in the rat hindlimb.

Skin sensory nerve nocifensor functions were investigated non-invasively in rats by measuring neurogenic inflammation and blister healing-rate after unilateral hindlimb denervation. Axon reflexes were evoked by transdermal iontophoresis of acetylcholine (ACh) or noxious electrical stimulation (TNS). Sodium nitroprusside (SNP) evoked direct dilator responses. Resultant changes in skin microvascular blood flux were measured by laser Doppler flowmetry. Compared with their sham-operated control limbs, denervation reduced inflammatory responses (ACh or TNS) by more than 85% and SNP responses by 28% (p < 0.05). Healing of dry-ice blisters raised on the hindpaw 14d post-denervation was significantly slower to complete healing (42d) than controls (26d) and initial inflammation was attenuated, confirming that innervation is important for inflammation and blister-healing.