Early developmental arrest of mammalian limbs lacking HoxA/HoxD gene function

Vertebrate HoxA and HoxD cluster genes are required for proper limb development. However, early lethality, compensation and redundancy have made a full assessment of their function difficult. Here we describe mice that are lacking all Hoxa and Hoxd functions in their forelimbs. We show that such limbs are arrested early in their developmental patterning and display severe truncations of distal elements, partly owing to the absence of Sonic hedgehog expression. These results indicate that the evolutionary recruitment of Hox gene function into growing appendages might have been crucial in implementing hedgehog signalling, subsequently leading to the distal extension of tetrapod appendages. Accordingly, these mutant limbs may be reminiscent of an ancestral trunk extension, related to that proposed for arthropods.     

Massive infection and loss of memory CD4+ T cells in multiple tissues during acute SIV infection

It has recently been established that both acute human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) infections are accompanied by a dramatic and selective loss of memory CD4+ T cells predominantly from the mucosal surfaces. The mechanism underlying this depletion of memory CD4+ T cells (that is, T-helper cells specific to previously encountered pathogens) has not been defined. Using highly sensitive, quantitative polymerase chain reaction together with precise sorting of different subsets of CD4+ T cells in various tissues, we show that this loss is explained by a massive infection of memory CD4+ T cells by the virus. Specifically, 30-60% of CD4+ memory T cells throughout the body are infected by SIV at the peak of infection, and most of these infected cells disappear within four days. Furthermore, our data demonstrate that the depletion of memory CD4+ T cells occurs to a similar extent in all tissues. As a consequence, over one-half of all memory CD4+ T cells in SIV-infected macaques are destroyed directly by viral infection during the acute phase-an insult that certainly heralds subsequent immunodeficiency. Our findings point to the importance of reducing the cell-associated viral load during acute infection through therapeutic or vaccination strategies.     

Coral record of increased sediment flux to the inner Great Barrier Reef since European settlement

The effect of European settlement on water quality in the Great Barrier Reef of Australia is a long-standing and controversial issue. Erosion and sediment transport in river catchments in this region have increased substantially since European settlement, but the magnitude of these changes remains uncertain. Here we report analyses of Ba/Ca ratios in long-lived Porites coral from Havannah Reef--a site on the inner Great Barrier Reef that is influenced by flood plumes from the Burdekin river--to establish a record of sediment fluxes from about 1750 to 1998. We find that, in the early part of the record, suspended sediment from river floods reached the inner reef area only occasionally, whereas after about 1870--following the beginning of European settlement--a five- to tenfold increase in the delivery of sediments is recorded with the highest fluxes occurring during the drought-breaking floods. We conclude that, since European settlement, land-use practices such as clearing and overstocking have led to major degradation of the semi-arid river catchments, resulting in substantially increased sediment loads entering the inner Great Barrier Reef.     

Mutation detection

The detection and characterization of mutations in genes has become a major area of interest in many areas of biology. Such variation may account for speciation, tumour formation, drug resistance, as well as the more obvious nature of inherited disease.     

Seasonal characteristics of the Indian Ocean Dipole during the Holocene epoch

The Indian Ocean Dipole (IOD)--an oscillatory mode of coupled ocean-atmosphere variability--causes climatic extremes and socio-economic hardship throughout the tropical Indian Ocean region. There is much debate about how the IOD interacts with the El Ni?o/Southern Oscillation (ENSO) and the Asian monsoon, and recent changes in the historic ENSO-monsoon relationship raise the possibility that the properties of the IOD may also be evolving. Improving our understanding of IOD events and their climatic impacts thus requires the development of records defining IOD activity in different climatic settings, including prehistoric times when ENSO and the Asian monsoon behaved differently from the present day. Here we use coral geochemical records from the equatorial eastern Indian Ocean to reconstruct surface-ocean cooling and drought during individual IOD events over the past approximately 6,500 years. We find that IOD events during the middle Holocene were characterized by a longer duration of strong surface ocean cooling, together with droughts that peaked later than those expected by El Ni?o forcing alone. Climate model simulations suggest that this enhanced cooling and drying was the result of strong cross-equatorial winds driven by the strengthened Asian monsoon of the middle Holocene. These IOD-monsoon connections imply that the socioeconomic impacts of projected future changes in Asian monsoon strength may extend throughout Australasia.