Regulation of Ovarian Function by the Germ Cell Specific DAZL Gene

The RNA binding protein DAZL (Deleted in Azoospermia) is essential for germ cell survival and subsequent fertility. The transgenic mouse DAZL model has confirmed that knockout (KO) females are infertile as a direct consequence of complete postnatal oocyte ablation. Interestingly, the heterozygous (Het) DAZL females have increased fertility giving rise to significantly more viable offspring, accompanied by significantly reduced plasma FSH and increased inhibin B compared to levels observed in the wildtype (Wt) females. Recent studies to identify putative DAZL mRNA targets suggest that DAZL may have multiple functions and mRNA targets throughout germ cell development. However, how this protein functions within the oocyte and how functional copy number gives rise to increased fertility remains to be fully elucidated.The studies in this thesis sought to identify putative DAZL mRNA targets in addition to molecular mechanisms which may be either affected direct or indirectly as a result of the functional copy number of DAZL (Wt or Het) within the oocyte or follicular unit. Oocytes from Wt and Het were evaluated for their expression of selected oocyte genes and comparative analysis suggests that oocyte gene expression is significantly altered between the genotypes. Genes of interest include Oospl and Hlfoo, both of which are down-regulated in mRNA expression in Het d21 oocytes and dlO ovaries compared to the Wt. Furthermore, an in silico bioinformatics approach was utilised to identify putative DAZL mRNA targets using a consensus DAZL binding sequence. One candidate target, PDCD4, previously identified as a tumour suppressor gene was selected for further investigation. Despite PDCD4 mRNA and protein being highly expressed within the ovary, no difference in mRNA levels between Het and Wt was observed. However, although not ruling out the possibility of being a DAZL target we now have evidence that PDCD4 can function within the steroidogenic cells of the corpus luteum in relation to functional luteolysis. Abstract Indirect actions of DAZL upon local regulation and response of follicle growth in culture were evaluated to investigate follicles at the gonadotrophin dependent stage of growth. Individual follicles from Wt and Het d21 mice were cultured in the presence of FSH at liu, 0.5iu, O.liu and O.Oliu for a six day period. Final follicle size/morphology did not differ between genotypes at liu, 0.5iu and O.liu of FSH, but by d3 at O.Oliu FSH growth o f Wt follicles was significantly (PO.OOl) perturbed compared to the Het. Despite no difference in final size between liu, 0.5iu, O.liu FSH treatments, mRNA analysis of individual follicles demonstrated a significant up-regulation of FSH receptor (P<0.05), aromatase (P<0.05) and inhibin PA (P<0.01) and a significant down-regulation in inhibin PB (P<0.01) expression in the Het follicles compared to the Wt, suggesting an increase in follicle maturity, sensitivity and hence suitability for selection as viable pre-ovulatory follicles. Furthermore, atresia rates from cultured follicles were significantly lower (P<0.05 (liu, O.liu FSH); P<0.01(0,01iu FSH)) in the Het compared to the Wt.These studies provide strong evidence that multiple mechanisms within the oocyte/follicle are directly and indirectly affected as a result of functional copy number of DAZL. Although direct in vivo targets remain to be identified it is clear that DAZL protein potentially targets multiple mRNAs at different stages of development, pre-programming the oocyte to increase the sensitivity of follicle and/or the functioning within a transcription complex regulating development. In conclusion, the beneficial consequences of increased fertility in the Het females is accompanied by a possible acceleration in oocyte and follicle maturation, an increased sensitivity to FSH in vitro with evidence of advanced stages of growth and, a reduction in follicle atresia. These differences support the suggestion that DAZL is having systemic effects on the paracrine communication within the follicle unit between the oocyte and somatic cells altering regulation and subsequent selection, and affecting final ovulation rate and litter size

Dexfenfluramine and the oestrogen-metabolizing enzyme CYP1B1 in the development of pulmonary arterial hypertension

&lt;p&gt;Aims: Pulmonary arterial hypertension (PAH) occurs more frequently in women than men. Oestrogen and the oestrogen-metabolising enzyme cytochrome P450 1B1 (CYP1B1) play a role in the development of PAH. Anorectic drugs such as dexfenfluramine (Dfen) have been associated with the development of PAH. Dfen mediates PAH via a serotonergic mechanism and we have shown serotonin to up-regulate expression of CYP1B1 in human pulmonary artery smooth muscle cells (PASMCs). Thus here we assess the role of CYP1B1 in the development of Dfen-induced PAH.&lt;/p&gt; &lt;p&gt;Methods and results: Dfen (5 mg kg−1 day−1 PO for 28 days) increased right ventricular pressure and pulmonary vascular remodelling in female mice only. Mice dosed with Dfen showed increased whole lung expression of CYP1B1 and Dfen-induced PAH was ablated in CYP1B1−/− mice. In line with this, Dfen up-regulated expression of CYP1B1 in PASMCs from PAH patients (PAH-PASMCs) and Dfen-mediated proliferation of PAH-PASMCs was ablated by pharmacological inhibition of CYP1B1. Dfen increased expression of tryptophan hydroxylase 1 (Tph1; the rate-limiting enzyme in the synthesis of serotonin) in PAH-PASMCs and both Dfen-induced proliferation and Dfen-induced up-regulation of CYP1B1 were ablated by inhibition of Tph1. 17β-Oestradiol increased expression of both Tph1 and CYP1B1 in PAH-PASMCs, and Dfen and 17β-oestradiol had synergistic effects on proliferation of PAH-PASMCs. Finally, ovariectomy protected against Dfen-induced PAH in female mice.&lt;/p&gt; &lt;p&gt;Conclusion: CYP1B1 is critical in the development of Dfen-induced PAH in mice in vivo and proliferation of PAH-PASMCs in vitro. CYP1B1 may provide a novel therapeutic target for PAH.&lt;/p&gt

Asteroseismology of the open clusters NGC 6791, NGC 6811, and NGC 6819 from nineteen months of Kepler photometry

We studied solar-like oscillations in 115 red giants in the three open clusters NGC 6791, NGC 6811, and NGC 6819, based on photometric data covering more than 19 months with NASA's Kepler space telescope. We present the asteroseismic diagrams of the asymptotic parameters \delta\nu_02, \delta\nu_01 and \epsilon, which show clear correlation with fundamental stellar parameters such as mass and radius. When the stellar populations from the clusters are compared, we see evidence for a difference in mass of the red giant branch stars, and possibly a difference in structure of the red clump stars, from our measurements of the small separations \delta\nu_02 and \delta\nu_01. Ensemble \'{e}chelle diagrams and upper limits to the linewidths of l = 0 modes as a function of \Delta\nu of the clusters NGC 6791 and NGC 6819 are also shown, together with the correlation between the l = 0 ridge width and the T_eff of the stars. Lastly, we distinguish between red giant branch and red clump stars through the measurement of the period spacing of mixed dipole modes in 53 stars among all the three clusters to verify the stellar classification from the color-magnitude diagram. These seismic results also allow us to identify a number of special cases, including evolved blue stragglers and binaries, as well as stars in late He-core burning phases, which can be potentially interesting targets for detailed theoretical modeling.Comment: 30 pages, 15 figures, 1 table, accepted to Ap

Temporal Changes in Ebola Transmission in Sierra Leone and Implications for Control Requirements: a Real-time Modelling Study.

BACKGROUND: Between August and November 2014, the incidence of Ebola virus disease (EVD) rose dramatically in several districts of Sierra Leone. As a result, the number of cases exceeded the capacity of Ebola holding and treatment centres. During December, additional beds were introduced, and incidence declined in many areas. We aimed to measure patterns of transmission in different regions, and evaluate whether bed capacity is now sufficient to meet future demand. METHODS: We used a mathematical model of EVD infection to estimate how the extent of transmission in the nine worst affected districts of Sierra Leone changed between 10th August 2014 and 18th January 2015. Using the model, we forecast the number of cases that could occur until the end of March 2015, and compared bed requirements with expected future capacity. RESULTS: We found that the reproduction number, R, defined as the average number of secondary cases generated by a typical infectious individual, declined between August and December in all districts. We estimated that R was near the crucial control threshold value of 1 in December. We further estimated that bed capacity has lagged behind demand between August and December for most districts, but as a consequence of the decline in transmission, control measures caught up with the epidemic in early 2015. CONCLUSIONS: EVD incidence has exhibited substantial temporal and geographical variation in Sierra Leone, but our results suggest that the epidemic may have now peaked in Sierra Leone, and that current bed capacity appears to be sufficient to keep the epidemic under-control in most districts

Kepler-432: a red giant interacting with one of its two long period giant planets

We report the discovery of Kepler-432b, a giant planet ($M_b = 5.41^{+0.32}_{-0.18} M_{\rm Jup}, R_b = 1.145^{+0.036}_{-0.039} R_{\rm Jup}$) transiting an evolved star $(M_\star = 1.32^{+0.10}_{-0.07} M_\odot, R_\star = 4.06^{+0.12}_{-0.08} R_\odot)$ with an orbital period of $P_b = 52.501129^{+0.000067}_{-0.000053}$ days. Radial velocities (RVs) reveal that Kepler-432b orbits its parent star with an eccentricity of $e = 0.5134^{+0.0098}_{-0.0089}$, which we also measure independently with asterodensity profiling (AP; $e=0.507^{+0.039}_{-0.114}$), thereby confirming the validity of AP on this particular evolved star. The well-determined planetary properties and unusually large mass also make this planet an important benchmark for theoretical models of super-Jupiter formation. Long-term RV monitoring detected the presence of a non-transiting outer planet (Kepler-432c; $M_c \sin{i_c} = 2.43^{+0.22}_{-0.24} M_{\rm Jup}, P_c = 406.2^{+3.9}_{-2.5}$ days), and adaptive optics imaging revealed a nearby (0\farcs87), faint companion (Kepler-432B) that is a physically bound M dwarf. The host star exhibits high signal-to-noise asteroseismic oscillations, which enable precise measurements of the stellar mass, radius and age. Analysis of the rotational splitting of the oscillation modes additionally reveals the stellar spin axis to be nearly edge-on, which suggests that the stellar spin is likely well-aligned with the orbit of the transiting planet. Despite its long period, the obliquity of the 52.5-day orbit may have been shaped by star-planet interaction in a manner similar to hot Jupiter systems, and we present observational and theoretical evidence to support this scenario. Finally, as a short-period outlier among giant planets orbiting giant stars, study of Kepler-432b may help explain the distribution of massive planets orbiting giant stars interior to 1 AU.Comment: 22 pages, 19 figures, 5 tables. Accepted to ApJ on Jan 24, 2015 (submitted Nov 11, 2014). Updated with minor changes to match published versio

Solving the mode identification problem in asteroseismology of F stars observed with Kepler

Asteroseismology of F-type stars has been hindered by an ambiguity in identification of their oscillation modes. The regular mode pattern that makes this task trivial in cooler stars is masked by increased linewidths. The absolute mode frequencies, encapsulated in the asteroseismic variable epsilon, can help solve this impasse because the values of epsilon implied by the two possible mode identifications are distinct. We find that the correct epsilon can be deduced from the effective temperature and the linewidths and we apply these methods to a sample of solar-like oscillators observed with Kepler.Comment: 7 pages, 4 figures, 1 table, accepted for publication in The Astrophysical Journal Letter

An asteroseismic membership study of the red giants in three open clusters observed by Kepler: NGC6791, NGC6819, and NGC6811

Studying star clusters offers significant advances in stellar astrophysics due to the combined power of having many stars with essentially the same distance, age, and initial composition. This makes clusters excellent test benches for verification of stellar evolution theory. To fully exploit this potential, it is vital that the star sample is uncontaminated by stars that are not members of the cluster. Techniques for determining cluster membership therefore play a key role in the investigation of clusters. We present results on three clusters in the Kepler field of view based on a newly established technique that uses asteroseismology to identify fore- or background stars in the field, which demonstrates advantages over classical methods such as kinematic and photometry measurements. Four previously identified seismic non-members in NGC6819 are confirmed in this study, and three additional non-members are found -- two in NGC6819 and one in NGC6791. We further highlight which stars are, or might be, affected by blending, which needs to be taken into account when analysing these Kepler data.Comment: 12 pages, 9 figures, 5 tables, accepted by Ap

Gravitational clustering of relic neutrinos and implications for their detection

We study the gravitational clustering of big bang relic neutrinos onto existing cold dark matter (CDM) and baryonic structures within the flat $\Lambda$CDM model, using both numerical simulations and a semi-analytical linear technique, with the aim of understanding the neutrinos' clustering properties for direct detection purposes. In a comparative analysis, we find that the linear technique systematically underestimates the amount of clustering for a wide range of CDM halo and neutrino masses. This invalidates earlier claims of the technique's applicability. We then compute the exact phase space distribution of relic neutrinos in our neighbourhood at Earth, and estimate the large scale neutrino density contrasts within the local Greisen--Zatsepin--Kuzmin zone. With these findings, we discuss the implications of gravitational neutrino clustering for scattering-based detection methods, ranging from flux detection via Cavendish-type torsion balances, to target detection using accelerator beams and cosmic rays. For emission spectroscopy via resonant annihilation of extremely energetic cosmic neutrinos on the relic neutrino background, we give new estimates for the expected enhancement in the event rates in the direction of the Virgo cluster.Comment: 38 pages, 8 embedded figures, iopart.cls; v2: references added, minor changes in text, to appear in JCA