133 research outputs found
Isolation, characterisation and in vitro potential of Oogonial stem cells
No full textThe longstanding belief that women are born with a finite ovarian reserve has been
debated for over a decade, ever since the discovery, and subsequent isolation, of
purported oogonial stem cells (OSCs) from adult mammalian ovaries. This rare cell
population has now been reported in the mouse, rat, pig, rhesus macaque monkey and
humans and, although a physiological role for the cells has not been proven, they do
appear to generate oocytes when cultured in specific environments, resulting in live
offspring in rodents. The primary aim of this thesis was to verify independently the
existence of OSCs in human ovary and determine whether they could be isolated from
a large animal model, the cow. The secondary aim was to investigate the cells’ in vitro
potential, both to undergo neo-oogenesis and as a model for germ cell development.
Putative bovine and human OSCs were isolated from disaggregated adult ovarian
cortex using a previously validated fluorescence-activated cell sorting (FACS)-based
technique, with cells sorted for externally expressed DDX4 (VASA). Freshly isolated
and cultured cells were characterised by analysing their expression of pluripotency and
germline markers, using RT-PCR, immunocytochemistry and Western blotting. The
in vitro neo-oogenesis potential of the cells was explored by injecting fluorescently
labelled cells into fragments of adult ovarian cortex and by forming aggregated
artificial “ovaries” with putative OSCs and fetal ovarian somatic cells. Germ cell
model experiments comprised treatment of cultured cells with BMP4 and/or retinoic
acid (RA), with subsequent quantitative RT-PCR and immunocytochemistry analysis
for downstream BMP4- and RA-response genes, and liposomal-mediated transfection
of cells with a DAZL overexpression plasmid to assess their meiosis-related gene
response.
Scarce populations of putative OSCs were retrieved from 5 human samples (aged 13-
40 years) and 6 bovine samples. The cells were cultured long-term for up to 7 months
and demonstrated consistent expression of several pluripotency-associated and
germline markers at the mRNA and protein level, including LIN28, NANOG,
POU5F1 (OCT4), IFITM3 (fragilis), STELLA, PRDM1 (BLIMP1), and C-KIT,
indicating their early germline nature. Investigation of neo-oogenesis potential
revealed that putative human OSCs were associated rarely with fetal somatic cells in
primordial follicle-like structures, but could not be confirmed to have undergone
oogenesis. However, like early germ cells, putative bovine and human OSCs were
BMP4 and RA responsive, with both species demonstrating significant upregulation
of expression of ID1 and bovine cells exhibiting a significant increase in MSX1, MSX2
and the meiotic marker SYCP3 in response to BMP4 and/or RA treatment. Cells could
be successfully transfected to overexpress DAZL; however, no significant downstream
gene expression changes were observed.
This is the first report of putative bovine OSC isolation and corroborates a previous
report showing putative human OSC isolation. Although the expression of both stem
cell and germline markers indicates the cells have characteristics of OSCs, their
capacity to enter meiosis and form functional oocytes has yet to be determined.
Putative bovine OSCs, however, show promise as a novel model for investigating germ
cell development. If their potential can be harnessed, then OSCs may have a role in
clinical applications, for example in fertility preservation, in the future. Future
experiments will examine the neo-oogenesis capabilities of the cells further and
explore novel cell delivery systems for clinical use
The impact of testosterone on the non-growing follicles and stroma in the transgender ovary
No full textThere is an increasing awareness of a need for fertility preservation measures for the transgender population prior to commencing gender affirming endocrine therapy. Current options for transgender men include embryo and oocyte cryopreservation but ovarian tissue cryopreservation may be a viable fertility preservation option for transgender men if immature follicles from removed ovarian cortex could be developed in vitro to maturity. However, there are few data on the effect of long-term exposure to high levels of testosterone as found in transgender men taking testosterone therapy on the non-growing follicles of the ovary.
Androgens are essential in normal ovarian function and follicle health, with androgen receptor expression found on the granulosa and theca cells as well as the oocyte. Androgens promote follicle growth, improve the responsiveness of granulosa cells to FSH and are an essential substrate for oestradiol production. However, an excess of androgen, as seen in polycystic ovary syndrome (PCOS), is associated with increased follicular recruitment with subsequent development arrest and anovulation, poor ovarian follicle health and subfertility. Hyperandrogenism as seen in PCOS and transgender men on testosterone therapy also drives changes within the ovarian stroma including thickening of the tunica albuginea, stromal cell hyperplasia and stromal cell luteinisation, contributing to reduced follicle maturation.
In this study, the effect of testosterone on the development, morphological health and DNA damage and repair capacity of human ovarian follicles in vivo and their survival in vitro was investigated. Potential alterations in the composition of the ovarian stroma as a result of testosterone exposure and how this can impact follicle growth and activation were also investigated.
Whole ovaries were obtained from transgender men taking pre-operative testosterone therapy (mean age: 27.6 ± 1.7 years; range 20-34 years, n = 8) at oophorectomy. This was compared to cortical biopsies from age-matched healthy women obtained at caesarean section (mean age: 31.8±1.5 years; range= 25-35 years, n=8). Cortical tissues were dissected into fragments and either fixed immediately for histological analysis or cultured for 6 days and subsequently fixed. Follicle classification and morphological health were evaluated from histological sections stained with haematoxylin and eosin (H&E) and expression of γH2AX as a marker of DNA damage by immunohistochemistry. Alteration of the composition of the ovarian stroma compared to control ovarian cortex was assessed by quantifying collagen deposition using histological stains picrosirius red and Masson’s Trichrome, and elastin deposition using immunofluorescence. Stromal cell density was quantified from H&E stained sections.
In uncultured tissue, testosterone exposure was associated with reduced follicle growth activation, poor follicle health and increased DNA damage. After 6 days of culture, there was enhanced follicle activation compared to control, but with further deterioration in morphological health and increased DNA damage. Transgender ovarian tissue had more collagen and less elastin compared to control with a subsequently higher collagen/elastin ratio, indicating tissue fibrosis. The stromal cell density was significantly higher in transgender tissue, in keeping with stromal cell hyperplasia.
The findings from this study indicate that high circulating concentrations of testosterone have effects on the primordial and small-growing follicles of the ovary. In addition, it was found that the ovaries of transgender men are more collagenous and less elastic, indicating tissue fibrosis. This enhanced tissue rigidity may contribute to reduced follicle activation in vivo and have implications on reproductive outcomes for transgender men considering pregnancy or fertility preservation measures
A coupled hidden Markov model for disease interactions
No full textTo investigate interactions between parasite species in a host, a population of field voles was studied longitudinally, with presence or absence of six different parasites measured repeatedly. Although trapping sessions were regular, a different set of voles was caught at each session, leading to incomplete profiles for all subjects. We use a discrete time hidden Markov model for each disease with transition probabilities dependent on covariates via a set of logistic regressions. For each disease the hidden states for each of the other diseases at a given time point form part of the covariate set for the Markov transition probabilities from that time point. This allows us to gauge the influence of each parasite species on the transition probabilities for each of the other parasite species. Inference is performed via a Gibbs sampler, which cycles through each of the diseases, first using an adaptive Metropolis–Hastings step to sample from the conditional posterior of the covariate parameters for that particular disease given the hidden states for all other diseases and then sampling from the hidden states for that disease given the parameters. We find evidence for interactions between several pairs of parasites and of an acquired immune response for two of the parasites
Cowpox virus infection in natural field vole Microtus agrestispopulations: significant negative impacts on survival
No full text1. Cowpox virus is an endemic virus circulating in populations of wild rodents. It has been implicated as a potential cause of population cycles in field voles Microtus agrestis L., in Britain, owing to a delayed density-dependent pattern in prevalence, but its impact on field vole demographic parameters is unknown. This study tests the hypothesis that wild field voles infected with cowpox virus have a lower probability of survival than uninfected individuals. 2. The effect of cowpox virus infection on the probability of an individual surviving to the next month was investigated using longitudinal data collected over 2 years from four grassland sites in Kielder Forest, UK. This effect was also investigated at the population level, by examining whether infection prevalence explained temporal variation in survival rates, once other factors influencing survival had been controlled for. 3. Individuals with a probability of infection, P(I), of 1 at a time when base survival rate was at median levels had a 22.4% lower estimated probability of survival than uninfected individuals, whereas those with a P(I) of 0.5 had a 10.4% lower survival. 4. At the population level, survival rates also decreased with increasing cowpox prevalence, with lower survival rates in months of higher cowpox prevalence. 5. Simple matrix projection models with 28 day time steps and two stages, with 71% of voles experiencing cowpox infection in their second month of life (the average observed seroprevalence at the end of the breeding season) predict a reduction in 28-day population growth rate during the breeding season from λ = 1.62 to 1.53 for populations with no cowpox infection compared with infected populations. 6. This negative correlation between cowpox virus infection and field vole survival, with its potentially significant effect on population growth rate, is the first for an endemic pathogen in a cyclic population of wild rodents
The rise of injecting drug use in East Africa: a case study from Kenya
No full textStudies on injecting drug use in East Africa are reviewed. The existingstudies document the spread of heroin injection in Kenya and Tanzania, both countries where HIV rates are high. No data from Uganda on injecting drug use was found by the authors. A case study of the growth of heroin injection in a Kenyan coastal town is presented. The need for needle-exchange programmes and other prevention services is discussed
An externally validated age-related model of mean follicle density in the cortex of the human ovary
No full textThe population of non-growing follicles present in the ovary is defined as the ovarian reserve. This underpins the reproductive lifespan in women, with its depletion determining age at loss of fertility and the menopause. Data amassed from published results of indirect invasive and non-invasive procedures has resulted in the generation of predictive models which estimate the ovarian reserve from conception throughout adult life. The distribution of follicles in the ovary is not uniform, with the great majority of NGFs located in the cortex, which is the region normally biopsied and used for fertility preservation. Previous models have however analysed whole ovary NGF populations and ovarian volumes, but not cortical NGF density. In this study we compared mean non-growing follicle density values obtained from tissue samples from 13 ovarian cortical biopsies (16-37 years) against age- matched model-predicted values generated from population and ovarian volume models, taking into account the proportion of the ovary that is cortex. A mean non-growing follicle density was calculated for each patient by counting all follicles in a given volume of freshly biopsied ovarian cortical tissue. These values were compared to age-matched model generated densities and the correlation between data sets tested. Non-growing follicle density values obtained from fresh biopsied ovarian cortex samples closely matched model generated data with low mean difference, tight agreement limits and no proportional error between the observed and predicted results. These findings validate the use of the population and ovarian volume models to accurately predict mean follicle density in the ovarian cortex of adult women.Peer reviewe
From Page to Performance Through Pedagogy: The Choral Legacy of Nancy Telfer
No full textNancy Telfer (b. 1950) is a celebrated Canadian composer, choral conductor, clinician, teacher, adjudicator, and author. Many of her approximately 240 works are performed internationally; some have become standard North American, European, and Asian festival and competition repertoire. Choral educators and conductors worldwide use her pedagogical materials. Telfer’s distinctive choral style, deeply rooted in her passion as a music educator, makes her works exemplary teaching and learning tools.
Much has been written about Telfer’s choral output and her music. No one, however, has yet explored connections between her pedagogical materials and her choral compositions. First, this study examines Telfer’s choral works and pedagogical materials, highlighting her inventiveness in using choral repertoire as a teaching tool for singers. Second, my research represents the first comprehensive study of Telfer’s choral legacy to encompass both her choral compositions and her choral pedagogy publications. I have worked closely with Telfer to produce an essential guide to her music, articulating appropriate performance practice of her works and illuminating the pedagogical philosophies that support her pieces.
I identified research on Telfer’s choral music and pedagogical writing, catalogued her choral compositions, and completed detailed analyses of representative works in four categories: compositions driven and/or inspired by text; pedagogically-based compositions; compositions evoking imagery; and noted concert pieces. I interviewed the composer to discuss her musical output, compositional process, and educational philosophy. I also spoke with prominent choral conductors who frequently program Telfer’s music in order to further understand the impact of her work. Ultimately, my study provides information on Telfer’s choral output, offers awareness, education, and support for the people who perform her works, bringing her music from the printed page to the performance stage with artistry and musicality.D.M.A
From Page to Performance Through Pedagogy: The Choral Legacy of Nancy Telfer
No full textNancy Telfer (b. 1950) is a celebrated Canadian composer, choral conductor, clinician, teacher, adjudicator, and author. Many of her approximately 240 works are performed internationally; some have become standard North American, European, and Asian festival and competition repertoire. Choral educators and conductors worldwide use her pedagogical materials. Telfer’s distinctive choral style, deeply rooted in her passion as a music educator, makes her works exemplary teaching and learning tools.
Much has been written about Telfer’s choral output and her music. No one, however, has yet explored connections between her pedagogical materials and her choral compositions. First, this study examines Telfer’s choral works and pedagogical materials, highlighting her inventiveness in using choral repertoire as a teaching tool for singers. Second, my research represents the first comprehensive study of Telfer’s choral legacy to encompass both her choral compositions and her choral pedagogy publications. I have worked closely with Telfer to produce an essential guide to her music, articulating appropriate performance practice of her works and illuminating the pedagogical philosophies that support her pieces.
I identified research on Telfer’s choral music and pedagogical writing, catalogued her choral compositions, and completed detailed analyses of representative works in four categories: compositions driven and/or inspired by text; pedagogically-based compositions; compositions evoking imagery; and noted concert pieces. I interviewed the composer to discuss her musical output, compositional process, and educational philosophy. I also spoke with prominent choral conductors who frequently program Telfer’s music in order to further understand the impact of her work. Ultimately, my study provides information on Telfer’s choral output, offers awareness, education, and support for the people who perform her works, bringing her music from the printed page to the performance stage with artistry and musicality.D.M.A
Maritime Insurgency and the Law of the Sea: An Analysis Using the Doctrine of Distress
No full textThis Comment examines the international legal implications of an insurgent warship operating on the high seas. The author specifically addresses the rights of insurgents to conduct maritime operations and the right of third States to deny use of the high seas to these insurgents. The author argues that these claims may be provided an adequate forum under the doctrine of distress, or force majeure. The author examines potential arguments that an insurgent warship is a private vessel, and is stateless, but concludes that an insurgent is neither. The author further concludes that an insurgent warship is not generally subject to lawful interference on the high seas by third States
Interference with Prospective Gain: Must There Be a Contract
No full textThis Comment examines the nature of the relationship required to establish a cause of action for interference with prospective economic gain. The author suggests that different jurisdictions have reached differing conclusions with respect to the importance of the existence of an enforceable contract as a basis for the establishment of liability. The author discusses the history behind this cause of action and looks at various explanations for the differing viewpoints, with specific focus on the positions taken by California and New York. The author concludes that the California approach, where liability is not dependent on the existence of a contract, is better suited to the modern commercial setting
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