Spermatogenesis is a classic model of cycling cell lineages that depend on a balance between stem cell self-renewal for continuity and the formation of progenitors as the initial step in the production of differentiated cells. The mechanisms that guide the continuum of spermatogonial stem cell (SSC) to progenitor spermatogonial transition and precise identifiers of subtypes in the process are undefined. Here we used an Id4-eGfp reporter mouse to discover that EGFP intensity is predictive of the subsets, with the ID4-EGFP Bright population being mostly, if not purely, SSCs, whereas the ID4-EGFP Dim population is in transition to the progenitor state. These subsets are also distinguishable by transcriptome signatures. Moreover, using a conditional overexpression mouse model, we found that transition from the stem cell to the immediate progenitor state requires downregulation of Id4 coincident with a major change in the transcriptome. Collectively, our results demonstrate that the level of ID4 is predictive of stem cell or progenitor capacity in spermatogonia and dictates the interface of transition between the different functional states.

With extended periods of time following ovulation, the metaphase II stage oocyte experiences deterioration in quality referred to as post-ovulatory oocyte ageing. Post-ovulatory ageing occurs both in vivo and in vitro and has been associated with reduced fertilization rates, poor embryo quality, post-implantation errors and abnormalities in the offspring. Although the physiological consequences of post-ovulatory oocyte ageing have largely been established, the molecular mechanisms controlling this process are not well defined. This review analyses the relationships between biochemical changes exhibited by the ageing oocyte and the symptoms associated with the ageing phenotype. We also discuss molecular events that are potentially involved in orchestrating post-ovulatory ageing with a particular focus on the role of oxidative stress. We propose that oxidative stress may act as the initiator for a cascade of events that create the aged oocyte phenotype. Specifically, oxidative stress has the capacity to cause a decline in levels of critical cell cycle factors such as maturation-promoting factor, impair calcium homoeostasis, induce mitochondrial dysfunction and directly damage multiple intracellular components of the oocyte such as lipids, proteins and DNA. Finally, this review addresses current strategies for delaying post-ovulatory oocyte ageing with a particular focus on the potential use of compounds such as caffeine or selected antioxidants in the development of more refined media for the preservation of oocyte integrity during IVF procedures.

Oxidative stress is known as a major contributing factor involved in oocyte aging, which negatively affects oocyte quality and development after fertilization. Melatonin is an effective free radical scavenger and its metabolites AFMK and AMK are powerful detoxifiers that eliminate free radicals. In this study, we used porcine oocytes to test the hypothesis that melatonin could scavenge free radicals produced during oocyte aging, thereby maintaining oocyte quality. We compared reactive oxygen species levels, apoptosis levels, mitochondrial membrane potential ratios, total glutathione contents and expression levels in fresh, aged and melatonin-treated aged porcine oocytes and observed the percentage of blastocyst formation following parthenogenetic activation. We found that melatonin could effectively maintain the morphology of oocytes observed in control oocytes, alleviate oxidative stress, markedly decrease early apoptosis levels, retard the decline of mitochondrial membrane potential and significantly promote subsequent embryonic development in oocytes aged for 24 hr in vitro. These results strongly suggest that melatonin can prevent postovulatory oocyte aging and promote subsequent embryonic development in the pig, which might find practical applications to control oocyte aging in other mammalian species including humans to maintain the quality of human oocytes when performing clinical assisted reproductive technology. www.aging-us.com 1553 AGING strategies to delay oocyte aging and increase the time that may be needed to manipulate oocytes to perform assisted reproductive technologies (ARTs).

SummaryOxidative stress is known to have a major impact on human sperm function and, as a result, there is a need to develop sensitive methods for measuring reactive oxygen species (ROS) generation by these cells. A variety of techniques have been developed for this purpose including chemiluminescence (luminol and lucigenin), flow cytometry (MitoSOX Red, dihydroethidium, 4,5‐diaminofluorescein diacetate and 2′,7′‐dichlorodihydrofluorescein diacetate) and spectrophotometry (nitroblue tetrazolium). The relative sensitivity of these assays and their comparative ability to detect ROS generated in different subcellular compartments of human spermatozoa, have not previously been investigated. To address this issue, we have compared the performance of these assays when ROS generation was triggered with a variety of reagents including 2‐hydroxyestradiol, menadione, 4‐hydroxynonenal and arachidonic acid. The results revealed that menadione predominantly induced release of ROS into the extracellular space where these metabolites could be readily detected by luminol‐peroxidase and, to a lesser extent, 2′,7′‐dichlorodihydrofluorescein. However, such sensitivity to extracellular ROS meant that these assays were particularly vulnerable to interference by leucocytes. The remaining reagents predominantly elicited ROS generation by the sperm mitochondria and could be optimally detected by MitoSOX Red and DHE. Examination of spontaneous ROS generation by defective human spermatozoa revealed that MitoSOX Red was the most effective indicator of oxidative stress, thereby emphasizing the general importance of mitochondrial dysregulation in the aetiology of defective sperm function.

Ensuring robust gamete production even in the face of environmental stress is of utmost importance for species survival, especially in mammals that have low reproductive rates. Here, we describe a family of genes called melanoma antigens (MAGEs) that evolved in eutherian mammals and are normally restricted to expression in the testis (http://MAGE.stjude.org) but are often aberrantly activated in cancer. Depletion of Mage-a genes disrupts spermatogonial stem cell maintenance and impairs repopulation efficiency in vivo. Exposure of Mage-a knockout mice to genotoxic stress or long-term starvation that mimics famine in nature causes defects in spermatogenesis, decreased testis weights, diminished sperm production, and reduced fertility. Last, human MAGE-As are activated in many cancers where they promote fuel switching and growth of cells. These results suggest that mammalian-specific MAGE genes have evolved to protect the male germline against environmental stress, ensure reproductive success under non-optimal conditions, and are hijacked by cancer cells.