18 research outputs found
Age Sequence in Small Clusters Associated with Bright-Rimmed Clouds
Bright-rimmed clouds (BRCs) found in H II regions are probable sites of
triggered star formation due to compression by ionization/shock fronts, and it
is hypothesized that star formation proceeds from the exciting star(s) side
outward of the HII region ("small-scale sequential star formation"). In order
to quantitatively testify this hypothesis we undertook BVIc photometry of four
BRC aggregates. The amounts of interstellar extinction and reddening for each
star have been estimated by using the JHKs photometry. Then we constructed
reddening-corrected V/V-Ic color-magnitude diagrams, where the age of each star
has been derived. All the stars turned out to be a few tenths to a few Myr old.
Although the scatters are large and the numbers of the sample stars are small,
we found a clear trend that the stars inside or in the immediate vicinity of
the bright rim are younger than those outside it in all the four aggregates,
confirming the hypothesis in question.Comment: 10 pages, 2 figures; accepted for publication in PAS
Interferometric Observations of the T Tauri Stars in the MBM 12 Cloud
We have carried out a millimeter interferometric continuum survey toward 7
YSOs in the MBM 12 cloud. Thermal emissions associated with 2 YSOs were
detected above the 3- level at 2.1 mm, and one also showed a 1.3 mm
thermal emission. Another object was marginally detected at 2.1 mm. Spectral
energy distributions of the YSOs are well fitted by a simple power-law disk
model. Masses of the circumstellar disks are estimated to be an order of 0.05
M_{\sun}. The circumstellar disks in the MBM 12 cloud have properties in
common with the disks in nearby star-forming regions, in terms of disk
parameters such as a disk mass, as well as an infrared excess.Comment: 9 pages, 3 figures, accepted by ApJ Letter
Unc-51/ATG1 Controls Axonal and Dendritic Development via Kinesin-Mediated Vesicle Transport in the Drosophila Brain
Background:Members of the evolutionary conserved Ser/Thr kinase Unc-51 family are key regulatory proteins that control neural development in both vertebrates and invertebrates. Previous studies have suggested diverse functions for the Unc-51 protein, including axonal elongation, growth cone guidance, and synaptic vesicle transport.Methodology/Principal Findings:In this work, we have investigated the functional significance of Unc-51-mediated vesicle transport in the development of complex brain structures in Drosophila. We show that Unc-51 preferentially accumulates in newly elongating axons of the mushroom body, a center of olfactory learning in flies. Mutations in unc-51 cause disintegration of the core of the developing mushroom body, with mislocalization of Fasciclin II (Fas II), an IgG-family cell adhesion molecule important for axonal guidance and fasciculation. In unc-51 mutants, Fas II accumulates in the cell bodies, calyx, and the proximal peduncle. Furthermore, we show that mutations in unc-51 cause aberrant overshooting of dendrites in the mushroom body and the antennal lobe. Loss of unc-51 function leads to marked accumulation of Rab5 and Golgi components, whereas the localization of dendrite-specific proteins, such as Down syndrome cell adhesion molecule (DSCAM) and No distributive disjunction (Nod), remains unaltered. Genetic analyses of kinesin light chain (Klc) and unc-51 double heterozygotes suggest the importance of kinesin-mediated membrane transport for axonal and dendritic development. Moreover, our data demonstrate that loss of Klc activity causes similar axonal and dendritic defects in mushroom body neurons, recapitulating the salient feature of the developmental abnormalities caused by unc-51 mutations.Conclusions/Significance:Unc-51 plays pivotal roles in the axonal and dendritic development of the Drosophila brain. Unc-51-mediated membrane vesicle transport is important in targeted localization of guidance molecules and organelles that regulate elongation and compartmentalization of developing neurons