44 research outputs found
The RNA recognition motif protein RBM11 is a novel tissue-specific splicing regulator.
Mammalian tissues display a remarkable complexity of splicing patterns. Nevertheless, only few examples of tissue-specific splicing regulators are known. Herein, we characterize a novel splicing regulator named RBM11, which contains an RNA Recognition Motif (RRM) at the amino terminus and a region lacking known homology at the carboxyl terminus. RBM11 is selectively expressed in brain, cerebellum and testis, and to a lower extent in kidney. RBM11 mRNA levels fluctuate in a developmentally regulated manner, peaking perinatally in brain and cerebellum, and at puberty in testis, in concomitance with differentiation events occurring in neurons and germ cells. Deletion analysis indicated that the RRM of RBM11 is required for RNA binding, whereas the carboxyl terminal region permits nuclear localization and homodimerization. RBM11 is localized in the nucleoplasm and enriched in SRSF2-containing splicing speckles. Transcription inhibition/release experiments and exposure of cells to stress revealed a dynamic movement of RBM11 between nucleoplasm and speckles, suggesting that its localization is affected by the transcriptional status of the cell. Splicing assays revealed a role for RBM11 in the modulation of alternative splicing. In particular, RBM11 affected the choice of alternative 5' splice sites in BCL-X by binding to specific sequences in exon 2 and antagonizing the SR protein SRSF1. Thus, our findings identify RBM11 as a novel tissue-specific splicing factor with potential implication in the regulation of alternative splicing during neuron and germ cell differentiation
Chromospheric activity among fast rotating M-dwarfs in the open cluster NGC 2516
We report radial velocities (RVs), projected equatorial velocities (v sin i)
and CaII triplet (CaT) chromospheric activity indices for 237 late-K to mid-M
candidate members of the young open cluster NGC 2516. These stars have rotation
periods between 0.1 and 15 days. Intermediate resolution spectra were obtained
using the Giraffe spectrograph at the Very Large Telescope. Membership was
confirmed on the basis of RVs for 210 targets. We see a marked increase in the
fraction of rapidly rotators as we move to cooler spectral types. About 20 per
cent of M0-M1 stars have v sin i >15km/s, increasing to 90 per cent of M4
stars. Activity indices derived from the first two lines of the CaT (8498A and
8542A) show differing dependencies on rotation period and mass for stars lying
above and below the fully convective boundary. Higher mass stars, of spectral
type K3-M2.5, show chromospheric activity which increases with decreasing
Rossby number (the ratio of period to convective turnover time), saturating for
Rossby numbers <0.1. For cooler stars, which are probably fully convective and
almost all of which have Rossby numbers <0.1, there is a clear decrease in
chromospheric activity as (V-I)_0 increases, amounting to a fall of about a
factor of 2-3 between spectral types M2.5 and M4. This decrease in activity
levels at low Rossby numbers is not seen in X-ray observations of the coronae
of cluster M-dwarfs or of active field M-dwarfs. There is no evidence for
supersaturation of chromospheric activity for stars of any spectral type at
Rossby numbers <0.01. We suggest that the fall in the limiting level of
chromospheric emission beyond spectral type M3 in NGC~2516 is, like the
simultaneous increase in rotation rates in field stars, associated with a
change in the global magnetic topology as stars approach the fully convective
boundary and not due to any decrease in dynamo-generated magnetic flux.Comment: Accepted for publication in MNRA
Chromosphere of K giant stars Geometrical extent and spatial structure detection
We aim to constrain the geometrical extent of the chromosphere of non-binary
K giant stars and detect any spatial structures in the chromosphere. We
performed observations with the CHARA interferometer and the VEGA beam combiner
at optical wavelengths. We observed seven non-binary K giant stars. We measured
the ratio of the radii of the photosphere to the chromosphere using the
interferometric measurements in the Halpha and the Ca II infrared triplet line
cores. For beta Ceti, spectro-interferometric observations are compared to an
non-local thermal equilibrium (NLTE) semi-empirical model atmosphere including
a chromosphere. The NLTE computations provide line intensities and contribution
functions that indicate the relative locations where the line cores are formed
and can constrain the size of the limb-darkened disk of the stars with
chromospheres. We measured the angular diameter of seven K giant stars and
deduced their fundamental parameters: effective temperatures, radii,
luminosities, and masses. We determined the geometrical extent of the
chromosphere for four giant stars. The chromosphere extents obtained range
between 16% to 47% of the stellar radius. The NLTE computations confirm that
the Ca II/849 nm line core is deeper in the chromosphere of ? Cet than either
of the Ca II/854 nm and Ca II/866 nm line cores. We present a modified version
of a semi-empirical model atmosphere derived by fitting the Ca II triplet line
cores of this star. In four of our targets, we also detect the signature of a
differential signal showing the presence of asymmetries in the chromospheres.
Conclusions. It is the first time that geometrical extents and structure in the
chromospheres of non-binary K giant stars are determined by interferometry.
These observations provide strong constrains on stellar atmosphere models.Comment: 10 pages, 12 figure
Chromospheric activity and rotation of FGK stars in the solar vicinity. An estimation of the radial velocity jitter
Context: Chromospheric activity produces both photometric and spectroscopic
variations that can be mistaken as planets. Large spots crossing the stellar
disc can produce planet-like periodic variations in the light curve of a star.
These spots clearly affect the spectral line profiles and their perturbations
alter the line centroids creating a radial velocity jitter that might
contaminate" the variations induced by a planet. Precise chromospheric activity
measurements are needed to estimate the activity-induced noise that should be
expected for a given star. Aims: We obtain precise chromospheric activity
measurements and projected rotational velocities for nearby (d < 25 pc) cool
(spectral types F to K) stars, to estimate their expected activity-related
jitter. As a complementary objective, we attempt to obtain relationships
between fluxes in different activity indicator lines, that permit a
transformation of traditional activity indicators, i.e, CaII H & K lines, to
others that hold noteworthy advantages. Methods: We used high resolution
(~50000) echelle optical spectra. To determine the chromospheric emission of
the stars in the sample, we used the spectral subtraction technique. Rotational
velocities were determined using the cross-correlation technique. To infer
activity-related radial velocity (RV) jitter, we used empirical relationships
between this jitter and the R'_HK index. Results: We measured chromospheric
activity, as given by different indicators throughout the optical spectra, and
projected rotational velocities for 371 nearby cool stars. We have built
empirical relationships among the most important chromospheric emission lines.
Finally, we used the measured chromospheric activity to estimate the expected
RV jitter for the active stars in the sample.Comment: Accepted for publication in Astronomy & Astrophysic
The young active star SAO 51891 (V383 Lac)
Our aim is investigating surface inhomogeneities of the young late-type star
SAO51891, from photosphere to upper chromosphere, analyzing contemporaneous
high-resolution spectra and broad-band photometry. The FOCES@CAHA spectral
range is used to determine spectral classification and derive vsini and Vrad.
The Li abundance is measured to estimate the age. The BVRIJHKs bands are used
to construct the SED. The variations of our BV fluxes and Teff are used to
infer the presence of photospheric spots and observe their behavior over time.
The chromospheric activity is studied applying the spectral subtraction
technique to Halpha, CaII H&K, Heps, and CaII IRT lines. We find SAO51891 to be
a young K0-1V star with Li abundance close to the Pleiades upper envelope,
confirming its youth (~100 Myr), also inferred from its kinematical membership
to the Local Association. We detect no IR excess from SED analysis, and
rotational modulation of luminosity, Teff, CaII, and Heps total fluxes. A spot
model with two active regions, ~240 K cooler than the surrounding photosphere,
fits our light/Teff curves, and reproduces the small-amplitude Vrad variations.
The anti-correlation of light curves and chromospheric diagnostics indicates
plages spatially associated with spots. The large amplitude observed in the
Heps-flux curve suggests that this line is very sensitive to the plage
presence. Finally, SAO51891 is a young active star, lacking significant amounts
of circumstellar dust or any evidence for low mass companions. The spots turn
out to be larger and warmer than those in less active MS stars. The Vrad
variation produced by spots has an amplitude comparable with those induced by
Jupiter-mass planets orbiting close to the star. SAO51891 is a good example of
star where the detection of planets may be hampered by the high activity level.Comment: 16 pages, 12 figures, 7 tables, accepted by Astronomy and
Astrophysics; abstract here was shortene
The effect of magnetic activity saturation in chromospheric flux-flux relationships
We present a homogeneous study of chromospheric and coronal flux-flux
relationships using a sample of 298 late-type dwarf active stars with spectral
types F to M. The chromospheric lines were observed simultaneously in each star
to avoid spread due to long term variability. Unlike other works, we subtract
the basal chromospheric contribution in all the spectral lines studied. For the
first time, we quantify the departure of dMe stars from the general relations.
We show that dK and dKe stars also deviate from the general trend. Studying the
flux-colour diagrams we demonstrate that the stars deviating from the general
relations are those with saturated X-ray emission and that those stars also
present saturation in the H line. Using several age spectral
indicators, we show that they are younger stars than those following the
general relationships. The non-universality of flux-flux relationships found in
this work should be taken into account when converting between fluxes in
different chromospheric activity indicators.Comment: Accepted for publication in the Monthly Notices of the Royal
Astronomical Societ
The RNA Binding Protein SAM68 Transiently Localizes in the Chromatoid Body of Male Germ Cells and Influences Expression of Select MicroRNAs
The chromatoid body (CB) is a unique structure of male germ cells composed of thin filaments that condense into a perinuclear organelle after meiosis. Due to the presence of proteins involved in different steps of RNA metabolism and of different classes of RNAs, including microRNAs (miRNAs), the CB has been recently suggested to function as an RNA processing centre. Herein, we show that the RNA binding protein SAM68 transiently localizes in the CB, in concomitance with the meiotic divisions of mouse spermatocytes. Precise staging of the seminiferous tubules and co-localization studies with MVH and MILI, two well recognized CB markers, documented that SAM68 transiently associates with the CB in secondary spermatocytes and early round spermatids. Furthermore, although SAM68 co-immunoprecipitated with MVH in secondary spermatocytes, its ablation did not affect the proper localization of MVH in the CB. On the other hand, ablation of the CB constitutive component MIWI did not impair association of SAM68 with the CB. Isolation of CBs from Sam68 wild type and knockout mouse testes and comparison of their protein content by mass spectrometry indicated that Sam68 ablation did not cause overall alterations in the CB proteome. Lastly, we found that SAM68 interacts with DROSHA and DICER in secondary spermatocytes and early round spermatids and that a subset of miRNAs were altered in Sam68−/−germ cells. These results suggest a novel role for SAM68 in the miRNA pathway during spermatogenesis