1,874 research outputs found
Progeny of Germ Line Knockouts of \u3cem\u3eASI2\u3c/em\u3e, a Gene Encoding a Putative Signal Transduction Receptor in \u3cem\u3eTetrahymena Thermophila\u3c/em\u3e, Fail to Make the Transition from Sexual Reproduction to Vegetative Growth
The ciliated protozoan Tetrahymena has two nuclei: a germ line micronucleus and a somatic macronucleus. The transcriptionally active macronucleus has about 50 copies of each chromosome. At sexual reproduction (conjugation), the parental macronucleus is degraded and new macronucleus develops from a mitotic product of the zygotic micronucleus. Development of the macronucleus involves massive genome remodeling, including deletion of about 6000 specific internal eliminated sequences (IES) and multiple rounds of DNA replication. A gene encoding a putative signal transduction receptor, ASI2, (anlagen stage induced 2) is up-regulated during development of the new macronuclei (anlagen). Macronuclear ASI2 is nonessential for vegetative growth. Homozygous ASI2 germ line knockout cells with wild type parental macronuclei proceed through mating but arrest at late macronuclear anlagen development and die before the first post-conjugation fission. IES elimination occurs in these cells. Two rounds of postzygotic DNA replication occur normally in progeny of ASI2 germ line knockouts, but endoreduplication of the macronuclear genome is arrested. The germ line ASI2 null phenotype is rescued in a mating of a knockout strain with wild type cells
Semi-analytical dark matter halos and the Jeans equation
Although N-body studies of dark matter halos show that the density profiles,
rho(r), are not simple power-laws, the quantity rho/sigma^3, where sigma(r) is
the velocity dispersion, is in fact a featureless power-law over ~3 decades in
radius. In the first part of the paper we demonstrate, using the semi-analytic
Extended Secondary Infall Model (ESIM), that the nearly scale-free nature of
rho/sigma^3 is a robust feature of virialized halos in equilibrium. By
examining the processes in common between numerical N-body and semi-analytic
approaches, we argue that the scale-free nature of rho/sigma^3 cannot be the
result of hierarchical merging, rather it must be an outcome of violent
relaxation. The empirical results of the first part of the paper motivate the
analytical work of the second part of the paper, where we use rho/sigma^3
proportional to r^{-alpha} as an additional constraint in the isotropic Jeans
equation of hydrostatic equilibrium. Our analysis shows that the constrained
Jeans equation has different types of solutions, and in particular, it admits a
unique ``periodic'' solution with alpha=1.9444. We derive the analytic
expression for this density profile, which asymptotes to inner and outer
profiles of rho ~ r^{-0.78}, and rho ~ r^{-3.44}, respectively.Comment: 37 pg, 14 fig. Accepted to ApJ: added two figures and extended
discussion. Note that an earlier related paper (conference proceedings)
astro-ph/0412442 has a mistake in eq.(2.2); the correct version is eq.(5) of
the present submissio
Variations, validations, degradations, and noninvasive determination of pregnancy using fecal steroid metabolites in free-ranging pronghorn
Pregnancy status is a key parameter used to assess reproductive performance of a species as it represents a starting point for measuring vital rates. Vital rates allow managers to determine trends in populations such as neonate survival and recruitment; two important factors in ungulate population growth rates. Techniques to determine pregnancy have generally involved capture and restraint of the animal to obtain blood samples for determining serum hormone levels. Non-invasive pregnancy assessment, via feces, eliminates any hazards between handler and animal, as well as removes handling-induced physiological biases. Using noninvasive fecal sampling, we conducted hormone validations, investigated pregnancy rates, and determined hormone degradation rates across five subpopulations of pronghorn (Antilocapra americana) in Idaho. Samples were collected during April-May of 2018 and 2019 from adult pronghorn of known sex and age class. Metabolites of testosterone, cortisol, 17β-estradiol, and progesterone were measured in fecal samples, and concentrations of estradiol and progesterone were examined for pregnancy determination. Average fecal progesterone metabolite (FPM) levels of pregnant females were more than double compared to levels of nonpregnant females. Fecal estrogen metabolite (FEM) levels did not differ during concurrent sampling. The largest difference in FPM levels between pregnant and nonpregnant females began on 28 April. Pregnancy determination sampling showed average FPM levels for all five subpopulations were significantly different than the nonpregnant female validation group. Nonetheless, pregnancy rates for some subpopulations lacked conclusive estimates due to early fecal sampling. Fecal glucocorticoid metabolites (FGM) levels significantly differed between pregnant females and male pronghorn, but did not differ from nonpregnant females. Degradation rates of FPM and FGM differed across days, with values for FPM from Day 1 being significantly different from all subsequent days, and after Day 9 for FGM, demonstrating the requirement of fresh samples to accurately measure hormone concentrations. We concluded that a noninvasive method to diagnosis pregnancy is possible in pronghorn via progesterone metabolites if fresh samples are collected during late gestation
Progeny of germ line knockouts of ASI2, a gene encoding a putative signal transduction receptor in Tetrahymena thermophila, fail to make the transition from sexual reproduction to vegetative growth
AbstractThe ciliated protozoan Tetrahymena has two nuclei: a germ line micronucleus and a somatic macronucleus. The transcriptionally active macronucleus has about 50 copies of each chromosome. At sexual reproduction (conjugation), the parental macronucleus is degraded and new macronucleus develops from a mitotic product of the zygotic micronucleus. Development of the macronucleus involves massive genome remodeling, including deletion of about 6000 specific internal eliminated sequences (IES) and multiple rounds of DNA replication. A gene encoding a putative signal transduction receptor, ASI2, (anlagen stage induced 2) is up-regulated during development of the new macronuclei (anlagen). Macronuclear ASI2 is nonessential for vegetative growth. Homozygous ASI2 germ line knockout cells with wild type parental macronuclei proceed through mating but arrest at late macronuclear anlagen development and die before the first post-conjugation fission. IES elimination occurs in these cells. Two rounds of postzygotic DNA replication occur normally in progeny of ASI2 germ line knockouts, but endoreduplication of the macronuclear genome is arrested. The germ line ASI2 null phenotype is rescued in a mating of a knockout strain with wild type cells
A Mutational Analysis of Conjugation inTetrahymena thermophila
AbstractConjugation in the freshwater ciliateTetrahymena thermophilainvolves a developmental program that models meiosis, fertilization, and early developmental events characteristic of multicellular eukaryotes. We describe a gallery of five early-acting conjugation mutations. These mutants,cnj1–5,exhibit phenotypes in which specific steps in the conjugal pathway have been altered or eliminated. Specifically,cnj1andcnj2fail to condense their micronuclear chromatin prior to each of the three prezygotic nuclear divisions. This results in nuclear division failure, failure to replicate DNA, and failure to initiate postzygotic development. Thecnj3mutant appears to exhibit a defect in chromosome separation during anaphase of mitosis.cnj4mutants successfully carry out meiosis I, yet are unable to execute the second meiotic division and abort all further development.cnj5mutants are unable to initiate either meiosis I or meiosis II, yet proceed to execute all subsequent developmental events. These mutant phenotypes are used to draw inferences regarding developmental dependencies that exist within the conjugation program
The Role of the Radial Orbit Instability in Dark Matter Halo Formation and Structure
For a decade, N-body simulations have revealed a nearly universal dark matter
density profile, which appears to be robust to changes in the overall density
of the universe and the underlying power spectrum. Despite its universality,
the physical origin of this profile has not yet been well understood.
Semi--analytic models by Barnes et al. (2005) have suggested that the density
structure of dark matter halos is determined by the onset of the radial orbit
instability (ROI). We have tested this hypothesis using N-body simulations of
collapsing dark matter halos with a variety of initial conditions. For
dynamically cold initial conditions, the resulting halo structures are triaxial
in shape, due to the mild aspect of the instability. We examine how variations
in initial velocity dispersion affect the onset of the instability, and find
that an isotropic velocity dispersion can suppress the ROI entirely, while a
purely radial dispersion does not. The quantity sigma^2/vc^2 is a criterion for
instability, where regions with sigma^2/vc^2 <~1 become triaxial due to the ROI
or other perturbations. We also find that the radial orbit instability sets a
scale length at which the velocity dispersion changes rapidly from isotropic to
radially anisotropic. This scale length is proportional to the radius at which
the density profile changes shape, as is the case in the semi--analytic models;
however, the coefficient of proportionality is different by a factor of ~2.5.
We conclude that the radial orbit instability is likely to be a key physical
mechanism responsible for the nearly universal profiles of simulated dark
matter halos.Comment: 13 pages, 12 figures, accepted to Ap
Dark Matter and Stellar Mass in the Luminous Regions of Disk Galaxies
We investigate the correlations among stellar mass (M_*), disk scale length
(R_d), and rotation velocity at 2.2 disk scale lengths (V_2.2) for a sample of
81 disk-dominated galaxies (disk/total >= 0.9) selected from the SDSS. We
measure V_2.2 from long-slit H-alpha rotation curves and infer M_* from galaxy
i-band luminosities (L_i) and g-r colors. We find logarithmic slopes of
2.60+/-0.13 and 3.05+/-0.12 for the L_i-V_2.2 and M_*-V_2.2 relations, somewhat
shallower than most previous studies, with intrinsic scatter of 0.13 dex and
0.16 dex. Our direct estimates of the total-to-stellar mass ratio within
2.2R_d, assuming a Kroupa IMF, yield a median ratio of 2.4 for M_*>10^10 Msun
and 4.4 for M_*=10^9-10^10 Msun, with large scatter at a given M_* and R_d. The
typical ratio of the rotation speed predicted for the stellar disk alone to the
observed rotation speed at 2.2R_d is ~0.65. The distribution of R_d at fixed
M_* is broad, but we find no correlation between disk size and the residual
from the M_*-V_2.2 relation, implying that this relation is an approximately
edge-on view of the disk galaxy fundamental plane. Independent of the assumed
IMF, this result implies that stellar disks do not, on average, dominate the
mass within 2.2R_d. We discuss our results in the context of infall models of
disk formation in cold dark matter halos. A model with a disk-to-halo mass
ratio m_d=0.05 provides a reasonable match to the R_d-M_* distribution for spin
parameters \lambda ranging from ~0.04-0.08, and it yields a reasonable match to
the mean M_*-V_2.2 relation. A model with m_d=0.1 predicts overly strong
correlations between disk size and M_*-V_2.2 residual. Explaining the wide
range of halo-to-disk mass ratios within 2.2R_d requires significant scatter in
m_d values, with systematically lower m_d for galaxies with lower .Comment: 18 pages, 2 tables, 7 figures, Accepted to ApJ, Table 1 updated,
otherwise minor change
African Americans' views on research and the Tuskegee Syphilis Study
The participation of African Americans in clinical and public health research is essential. However, for a multitude of reasons, participation is low in many research studies. This article reviews the literature that substantiates barriers to participation and the legacy of past abuses of human subjects through research. The article then reports the results of seven focus groups with 60 African Americans in Los Angeles, Chicago, Washington, DC, and Atlanta during the winter of 1997. In order to improve recruitment and retention in research, the focus group study examined knowledge of and attitudes toward medical research, knowledge of the Tuskegee Syphilis Study, and reactions to the Home Box Office production, Miss Evers' Boys, a fictionalized version of the Tuskegee Study, that premiered in February, 1997. The study found that accurate knowledge about research was limited; lack of understanding and trust of informed consent procedures was problematic; and distrust of researchers posed a substantial barrier to recruitment. Additionally, the study found that, in general, participants believed that research was important, but they clearly distinguished between types of research they would be willing to consider participating in and their motivations for doing so
Changes in Fecal Glucocorticoid Metabolites in Captive Coyotes (\u3ci\u3eCanis latrans\u3c/i\u3e): Influence of Gender, Time, and Reproductive Status
Reproduction is considered an energetically and physiologically demanding time in the life of an animal. Changes in physiological stress are partly reflected in changes in glucocorticoid metabolites and can be measured from fecal samples. We examined levels of fecal glucocorticoid metabolites (fGCMs) in 24 captive coyotes (Canis latrans) to investigate responses to the demands of reproduction. Using 12 pairs of coyotes (five pairs produced pups, seven pairs did not), we analyzed 633 fecal samples covering 11 biological periods (e.g., breeding, gestation, and lactation). Levels of fGCMs showed high individual variability, with females having higher fGCM levels than males. The production of pups showed no statistical effect on fGCM levels among females or males. Among females, fGCM levels were highest during 4–6 weeks of gestation compared to other periods but were not significantly different between pregnant and nonpregnant females. Among males, the highest fGCM levels were during 1–3 weeks of gestation compared to other periods, but were not significantly different between males with a pregnant mate versus nonpregnant mate. Of females producing pups, litter size did not influence fGCM levels. Given that they were fed ample food throughout the year, we found that the demands of producing pups did not appear to statistically influence measures of fGCM concentrations in captive coyotes
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