Spermatogonial Stem Cell Niche and Spermatogonial Stem Cell Transplantation in Zebrafish

Background Spermatogonial stem cells (SSCs) are the foundation of spermatogenesis, and reside within a specific microenvironment in the testes called “niche” which regulates stem cell properties, such as, self-renewal, pluripotency, quiescence and their ability to differentiate. Methodology/Principal Findings Here, we introduce zebrafish as a new model for the study of SSCs in vertebrates. Using 5′-bromo-2′-deoxyuridine (BrdU), we identified long term BrdU-retaining germ cells, type A undifferentiated spermatogonia as putative stem cells in zebrafish testes. Similar to rodents, these cells were preferentially located near the interstitium, suggesting that the SSC niche is related to interstitial elements and might be conserved across vertebrates. This localization was also confirmed by analyzing the topographical distribution of type A undifferentiated spermatogonia in normal, vasa::egfp and fli::egfp zebrafish testes. In the latter one, the topographical arrangement suggested that the vasculature is important for the SSC niche, perhaps as a supplier of nutrients, oxygen and/or signaling molecules. We also developed an SSC transplantation technique for both male and female recipients as an assay to evaluate the presence, biological activity, and plasticity of the SSC candidates in zebrafish. Conclusions/Significance We demonstrated donor-derived spermato- and oogenesis in male and female recipients, respectively, indicating the stemness of type A undifferentiated spermatogonia and their plasticity when placed into an environment different from their original niche. Similar to other vertebrates, the transplantation efficiency was low. This might be attributed to the testicular microenvironment created after busulfan depletion in the recipients, which may have caused an imbalance between factors regulating self-renewal or differentiation of the transplanted SSCs

Measurement of the diffractive structure function in deep inelastic scattering at HERA

This paper presents an analysis of the inclusive properties of diffractive deep inelastic scattering events produced in $ep$ interactions at HERA. The events are characterised by a rapidity gap between the outgoing proton system and the remaining hadronic system. Inclusive distributions are presented and compared with Monte Carlo models for diffractive processes. The data are consistent with models where the pomeron structure function has a hard and a soft contribution. The diffractive structure function is measured as a function of \xpom, the momentum fraction lost by the proton, of $\beta$, the momentum fraction of the struck quark with respect to \xpom, and of $Q^2$. The \xpom dependence is consistent with the form \xpoma where $a~=~1.30~\pm~0.08~(stat)~^{+~0.08}_{-~0.14}~(sys)$ in all bins of $\beta$ and $Q^2$. In the measured $Q^2$ range, the diffractive structure function approximately scales with $Q^2$ at fixed $\beta$. In an Ingelman-Schlein type model, where commonly used pomeron flux factor normalisations are assumed, it is found that the quarks within the pomeron do not saturate the momentum sum rule.Comment: 36 pages, latex, 11 figures appended as uuencoded fil

Observation of hard scattering in photoproduction events with a large rapidity gap at HERA

Events with a large rapidity gap and total transverse energy greater than 5 GeV have been observed in quasi-real photoproduction at HERA with the ZEUS detector. The distribution of these events as a function of the $\gamma p$ centre of mass energy is consistent with diffractive scattering. For total transverse energies above 12 GeV, the hadronic final states show predominantly a two-jet structure with each jet having a transverse energy greater than 4 GeV. For the two-jet events, little energy flow is found outside the jets. This observation is consistent with the hard scattering of a quasi-real photon with a colourless object in the proton.Comment: 19 pages, latex, 4 figures appended as uuencoded fil

mTOR: from growth signal integration to cancer, diabetes and ageing

In all eukaryotes, the target of rapamycin (TOR) signalling pathway couples energy and nutrient abundance to the execution of cell growth and division, owing to the ability of TOR protein kinase to simultaneously sense energy, nutrients and stress and, in metazoans, growth factors. Mammalian TOR complex 1 (mTORC1) and mTORC2 exert their actions by regulating other important kinases, such as S6 kinase (S6K) and Akt. In the past few years, a significant advance in our understanding of the regulation and functions of mTOR has revealed the crucial involvement of this signalling pathway in the onset and progression of diabetes, cancer and ageing.National Institutes of Health (U.S.)Howard Hughes Medical InstituteWhitehead Institute for Biomedical ResearchJane Coffin Childs Memorial Fund for Medical Research (Postdoctoral Fellowship)Human Frontier Science Program (Strasbourg, France

Alteration of AKT Activity Increases Chemotherapeutic Drug and Hormonal Resistance in Breast Cancer yet Confers an Achilles Heel by Sensitization to Targeted Therapy

The PI3K/PTEN/Akt/mTOR pathway plays critical roles in the regulation of cell growth. The effects of this pathway on drug resistance and cellular senescence of breast cancer cells has been a focus of our laboratory. Introduction of activated Akt or mutant PTEN constructs which lack lipid phosphatase [PTEN(G129E)] or lipid and protein phosphatase [PTEN(C124S)] activity increased the resistance of the cells to the chemotherapeutic drug doxorubicin, and the hormonal drug tamoxifen. Activated Akt and PTEN genes also inhibited the induction of senescence after doxorubicin treatment; a phenomenon associated with unrestrained proliferation and tumorigenesis. Interference with the lipid phosphatase domain of PTEN was sufficient to activate Akt/mTOR/p70S6K as MCF-7 cells transfected with the mutant PTEN gene lacking the lipid phosphatase activity [PTEN(G129E)] displayed elevated levels of activated Akt and p70S6K compared to empty vector transfected cells. Cells transfected with mutant PTEN or Akt constructs were hypersensitive to mTOR inhibitors when compared with the parental or empty vector transfected cells. Akt-transfected cells were cultured for over two months in tamoxifen from which tamoxifen and doxorubicin resistant cells were isolated that were >10-fold more resistant to tamoxifen and doxorubicin than the original Akt-transfected cells. These cells had a decreased induction of both activated p53 and total p21Cip1 upon doxorubicin treatment. Furthermore, these cells had an increased inactivation of GSK-3β and decreased expression of the estrogen receptor-α. In these drug resistant cells, there was an increased activation of ERK which is associated with proliferation. These drug resistant cells were hypersensitive to mTOR inhibitors and also sensitive to MEK inhibitors, indicating that the enhanced p70S6K and ERK expression was relevant to their drug and hormonal resistance. Given that Akt is overexpressed in greater than 50% of breast cancers, our results point to potential therapeutic targets, mTOR and MEK. These studies indicate that activation of the Akt kinase or disruption of the normal activity of the PTEN phosphatase can have dramatic effects on activity of p70S6K and other downstream substrates and thereby altering the therapeutic sensitivity of breast cancer cells. The effects of doxorubicin and tamoxifen on induction of the Raf/MEK/ERK and PI3K/Akt survival pathways were examined in unmodified MCF-7 breast cells. Doxorubicin was a potent inducer of activated ERK and to a lesser extent Akt. Tamoxifen also induced ERK. Thus a consequence of doxorubicin and tamoxifen therapy of breast cancer is the induction of a pro-survival pathway which may contribute to the development of drug resistance. Unmodified MCF-7 cells were also sensitive to MEK and mTOR inhibitors which synergized with both tamoxifen and doxorubicin to induce death. In summary, our results point to the key interactions between the PI3K/PTEN/Akt/mTOR and Raf/ MEK/ERK pathways in regulating chemotherapeutic drug resistance/sensitivity in breast cancer and indicate that targeting these pathways may prevent drug and hormonal resistance. Orignally published Advances in Enzyme Regulation, Vol. 48, No. 1, 2008

Population of Merging Compact Binaries Inferred Using Gravitational Waves through GWTC-3

We report on the population properties of compact binary mergers inferred from gravitational-wave observations of these systems during the first three LIGO-Virgo observing runs. The Gravitational-Wave Transient Catalog 3 (GWTC-3) contains signals consistent with three classes of binary mergers: binary black hole, binary neutron star, and neutron star-black hole mergers. We infer the binary neutron star merger rate to be between 10 and 1700 Gpc-3 yr-1 and the neutron star-black hole merger rate to be between 7.8 and 140 Gpc-3 yr-1, assuming a constant rate density in the comoving frame and taking the union of 90% credible intervals for methods used in this work. We infer the binary black hole merger rate, allowing for evolution with redshift, to be between 17.9 and 44 Gpc-3 yr-1 at a fiducial redshift (z=0.2). The rate of binary black hole mergers is observed to increase with redshift at a rate proportional to (1+z)κ with κ=2.9-1.8+1.7 for z≲1. Using both binary neutron star and neutron star-black hole binaries, we obtain a broad, relatively flat neutron star mass distribution extending from 1.2-0.2+0.1 to 2.0-0.3+0.3M⊙. We confidently determine that the merger rate as a function of mass sharply declines after the expected maximum neutron star mass, but cannot yet confirm or rule out the existence of a lower mass gap between neutron stars and black holes. We also find the binary black hole mass distribution has localized over- and underdensities relative to a power-law distribution, with peaks emerging at chirp masses of 8.3-0.5+0.3 and 27.9-1.8+1.9M⊙. While we continue to find that the mass distribution of a binary's more massive component strongly decreases as a function of primary mass, we observe no evidence of a strongly suppressed merger rate above approximately 60M⊙, which would indicate the presence of a upper mass gap. Observed black hole spins are small, with half of spin magnitudes below χi≈0.25. While the majority of spins are preferentially aligned with the orbital angular momentum, we infer evidence of antialigned spins among the binary population. We observe an increase in spin magnitude for systems with more unequal-mass ratio. We also observe evidence of misalignment of spins relative to the orbital angular momentum

All-sky search for long-duration gravitational-wave bursts in the third Advanced LIGO and Advanced Virgo run

After the detection of gravitational waves from compact binary coalescences, the search for transient gravitational-wave signals with less well-defined waveforms for which matched filtering is not well suited is one of the frontiers for gravitational-wave astronomy. Broadly classified into “short” ≲1  s and “long” ≳1  s duration signals, these signals are expected from a variety of astrophysical processes, including non-axisymmetric deformations in magnetars or eccentric binary black hole coalescences. In this work, we present a search for long-duration gravitational-wave transients from Advanced LIGO and Advanced Virgo’s third observing run from April 2019 to March 2020. For this search, we use minimal assumptions for the sky location, event time, waveform morphology, and duration of the source. The search covers the range of 2–500 s in duration and a frequency band of 24–2048 Hz. We find no significant triggers within this parameter space; we report sensitivity limits on the signal strength of gravitational waves characterized by the root-sum-square amplitude hrss as a function of waveform morphology. These hrss limits improve upon the results from the second observing run by an average factor of 1.8

Open data from the third observing run of LIGO, Virgo, KAGRA and GEO

The global network of gravitational-wave observatories now includes five detectors, namely LIGO Hanford, LIGO Livingston, Virgo, KAGRA, and GEO 600. These detectors collected data during their third observing run, O3, composed of three phases: O3a starting in April of 2019 and lasting six months, O3b starting in November of 2019 and lasting five months, and O3GK starting in April of 2020 and lasting 2 weeks. In this paper we describe these data and various other science products that can be freely accessed through the Gravitational Wave Open Science Center at https://gwosc.org. The main dataset, consisting of the gravitational-wave strain time series that contains the astrophysical signals, is released together with supporting data useful for their analysis and documentation, tutorials, as well as analysis software packages.Comment: 27 pages, 3 figure