A dearth of dark matter in ordinary elliptical galaxies

The kinematics of the outer parts of three intermediate-luminosity elliptical galaxies were studied with the Planetary Nebula Spectrograph. The galaxies' velocity-dispersion profiles were found to decline with the radius, and dynamical modeling of the data indicates the presence of little if any dark matter in these galaxies' halos. This unexpected result conflicts with findings in other galaxy types and poses a challenge to current galaxy formation theories.     

Cloning of complementary DNA for GAP-43, a neuronal growth-related protein

GAP-43 is one of a small subset of cellular proteins selectively transported by a neuron to its terminals. Its enrichment in growth cones and its increased levels in developing or regenerating neurons suggest that it has an important role in neurite growth. A complementary DNA (cDNA) that encodes rat GAP-43 has been isolated to study its structural characteristics and regulation. The predicted molecular size is 24 kilodaltons, although its migration in SDS-polyacrylamide gels is anomalously retarded. Expression of GAP-43 is limited to the nervous system, where its levels are highest during periods of neurite outgrowth. Nerve growth factor or adenosine 3',5'-monophosphate induction of neurites from PC12 cells is accompanied by increased GAP-43 expression. GAP-43 RNA is easily detectable, although at diminished levels, in the adult rat nervous system. This regulation of GAP-43 is concordant with a role in growth-related processes of the neuron, processes that may continue in the mature animal.     

A protein induced during nerve growth (GAP-43) is a major component of growth-cone membranes

Growth cones are specialized structures that form the distal tips of growing axons. During both normal development of the nervous system and regeneration of injured nerves, growth cones are essential for elongation and guidance of growing axons. Developmental and regenerative axon growth is frequently accompanied by elevated synthesis of a protein designated GAP-43. GAP-43 has now been found to be a major component of growth-cone membranes in developing rat brains. Relative to total protein, GAP-43 is approximately 12 times as abundant in growth-cone membranes as in synaptic membranes from adult brains. Immunohistochemical localization of GAP-43 in frozen sections of developing brain indicates that the protein is specifically associated with neuropil areas containing growth cones and immature synaptic terminals. The results support the proposal that GAP-43 plays a role in axon growth.     

The baryon halo of the milky way: A fossil record of its formation

Astronomers believe that the baryon (stellar) halo of the Milky Way retains a fossil imprint of how it was formed. But a vast literature shows that the struggle to interpret the observations within a consistent framework continues. The evidence indicates that the halo has built up through a process of accretion and merging over billions of years, which is still going on at a low level. Future satellite missions to derive three-dimensional space motions and heavy element (metal) abundances for a billion stars will disentangle the existing web and elucidate how galaxies like our own came into existence.     

Genetic conversion of a fungal plant pathogen to a nonpathogenic, endophytic mutualist

The filamentous fungal ascomycete Colletotrichum magna causes anthracnose in cucurbit plants. Isolation of a nonpathogenic mutant of this species (path-1) resulted in maintained wild-type levels of in vitro sporulation, spore adhesion, appressorial formation, and infection. Path-1 grew throughout host tissues as an endophyte and retained the wild-type host range, which indicates that the genetics involved in pathogenicity and host specificity are distinct. Prior infection with path-1 protected plants from disease caused by Colletotrichum and Fusarium.Genetic analysis of a cross between path-1 and wild-type strains indicated mutation of a single locus.