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R G Roberts

Publications and source records attributed to R G Roberts.

At least 19 recordsLinked to original sources
PubMed2005

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.

Aging↗
PubMed2004

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.

Animals↗
PubMed2003

Minor or major?

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Humans↗
PubMed2003

Effect of insulin upon protein degradation in cultured human myocytes.

BACKGROUND: The anabolic effects of insulin are well recognized but the mechanism by which insulin decreases muscle protein degradation in human is unclear. However, in a variety of catabolic conditions it is believed to be changes in the activity of the ATP-dependent ubiquitin proteolytic pathway that are responsible for changes in protein degradation in skeletal muscle. The aim of this study was to test the hypothesis that insulin regulates the ATP-dependent ubiquitin proteolytic pathway in human muscle. MATERIAL AND METHODS: The effects of insulin and acidosis on protein degradation were measured in human myocytes using L-[14C]phenylalanine. The effect of insulin on the activity of the ATP-dependent ubiquitin pathway was assessed from the mRNA expression of ubiquitin and the ubiquitin-conjugating enzyme E214k in human myocytes. RESULTS AND CONCLUSIONS: Coincubation of human myocytes with 100 nM of insulin was associated with a significant reduction in protein degradation. Metabolic acidosis is known to increase skeletal muscle protein degradation rates, and in our experiments protein degradation at a pH of 7.0 was significantly higher than pH 7.35. Eight-hour exposure to 100 nM of insulin resulted in a significant reduction in the expression of E214k but no change in the expression of ubiquitin. CONCLUSIONS: In human muscle we have demonstrated regulation by insulin of the ATP-dependent ubiquitin pathway at the level of ubiquitin conjugation.

Cells, Cultured↗
PubMed2002

Sodium bicarbonate treatment and ubiquitin gene expression in acidotic human subjects with chronic renal failure.

BACKGROUND: In chronic renal failure, metabolic acidosis is associated with increased whole body protein degradation. In rats this effect of acidosis occurs in skeletal muscle and is associated with increased ubiquitin mRNA expression. This has not been demonstrated in humans. MATERIALS AND METHODS: Six patients with chronic renal failure and acidosis underwent muscle biopsy before and after 1 month's treatment with sodium bicarbonate. RNA was extracted from the biopsy, and the expression of the genes for ubiquitin and the proteasome component, C2, were measured by Northern blotting. RESULTS AND CONCLUSIONS: There was no significant difference in the expression of ubiquitin or C2 after bicarbonate treatment. This is contrast with results from animal models of acidosis and some other catabolic conditions in humans. This may reflect the complexity of the ubiquitin-dependent pathway, and it may be that changes in ubiquitin expression are only seen with more severe and/or acute changes in pH.

Acidosis↗
PubMed2002

Indomethacin--a review of its role in the management of traumatic brain injury.

OBJECTIVE: To review the use of indomethacin in the management of traumatic brain injury. DATA SOURCES: Articles reported from 1966 to 2001 and identified through a MEDLINE search of the English language literature on the use of indomethacin in traumatic brain injury. SUMMARY OF REVIEW: Traumatic brain injury (TBI) is a frequent cause of mortality and morbidity in patients with head injury. The use of indomethacin in treating raised intracranial pressure (ICP) secondary to TBI is controversial. Clinical studies suggest that it may be useful in the management of intracranial hypertension, when used in combination with standard techniques, by decreasing cerebral blood flow and reducing ICP during the restoration of the blood brain barrier. Its unique mechanism of action may be due to precapillary vasoconstriction, which reduces the transcapillary transfer of fluid into the cerebral extracellular space. However, large, prospective, randomised and controlled studies have not yet been performed to confirm its benefit in patients with TBI. CONCLUSIONS: Indomethacin should only be considered as an experimental therapy for refractory intracranial hypertension in TBI patients, as current evidence is not available to support its routine use in the management of an elevated ICP. Its use in patients with cerebral vasospasm, renal failure, bleeding disorders, peptic ulceration and coagulopathies is contraindicated.

Journal Article↗
PubMed2001

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.

Animals↗
PubMed2001

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.

Animals↗
PubMed2001

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.

Alternative Splicing↗
PubMed2001

Dystrophins and dystrobrevins.

SUMMARY: A unique arrangement of domains makes up the common region of two otherwise very different proteins - long, elegant dystrophin, and its rather dumpy distant cousin, dystrobrevin. The two work in concert, forming the core of a large membrane-bound complex in all metazoa. Like many proteins, dystrophin and dystrobrevin have diversified in the vertebrate clade, as have their binding partners, yielding specialized complexes tailored to different cellular and subcellular locations. Disruption of several components of the complex is known to result in syndromes that include progressive myopathy, sometimes combined with cognitive defects; the best known of these is Duchenne muscular dystrophy. Despite a wealth of biochemical, cell biological and genetic information, the precise role of dystrophins, dystrobrevins and their collaborators remains unclear.

Animals↗
PubMed2001

Long mutant dystrophins and variable phenotypes: evasion of nonsense-mediated decay?

More than 98% of Duchenne muscular dystrophy (DMD) mutations result in the premature termination of the dystrophin open reading frame at various points over its 11-kb length. Despite this wide variation in coding potential (0%-98.6% of the full-length protein), the truncating mutations are associated with a surprisingly uniform severity of phenotype. This uniformity is probably attributable to ablation of the message by nonsense-mediated decay (NMD). The rare truncating mutations that occur near the 3' end of the dystrophin gene (beyond exon 70) can however result in extremely variable phenotypes (both intra- and inter-familially). We suggest that all proteins encoded by such mutant genes are capable in principle of rescuing the DMD phenotype but that NMD abrogates the opportunity to effect this rescue. The observed variability may therefore reflect an underlying variation in the efficiency of NMD between individuals. We discuss this hypothesis with particular reference to a well-characterised Becker muscular dystrophy patient with a frameshift mutation, where expression of a truncated dystrophin rescues the muscular but not mental phenotype.

Adolescent↗