Recent Arguments Against Germ Cell Renewal in the Adult Human Ovary: Is an Absence of Marker Gene Expression Really Acceptable Evidence of an Absence of Oogenesis?

In 2004, a study from our lab published in the journal Nature re-ignited a worldwide debate over the validity of the dogma that mammalian females are incapable of oocyte and follicle production during postnatal life. Amidst widespread skepticism, we forged ahead and published a second study in 2005 in the journal Cell, which not only reaffirmed with different experimental approaches that this dogma is invalid but also identified cells in bone marrow (BM) and blood of adult female mice that could generate oocytes contained within immature follicles in the ovaries of recipient females following transplantation. Although this work has been the subject of extensive critical commentary as well, two recent reports from others have confirmed the germline potential of adult BM-derived cells in mice. Further, independent corroboration of the results and conclusions presented in our earlier Nature paper is also now available. However, two papers have been published that purportedly question our work and conclusions. The first is a paper by Eggan et al. published in the journal Nature, which attempts to draw conclusions about the germline potential of BM-derived cells after focusing solely on ovulated eggs while ignoring what may be occurring at the level of oogenesis in the ovaries. The second is a report from Liu et al. just released in the journal Developmental Biology that claims to provide evidence refuting the possibility that adult female mammals produce new oocytes. However, all of the data presented in this latter report are derived from gene expression studies that the authors say fail to show the occurrence of meiosis or germ cell mitosis in adult human ovaries. Given that more than three years have past since our initial study challenging the dogma was published, it is our belief that continuing arguments against the possibility of postnatal oogenesis in mammals should be based on more rigorous experimental approaches than simply an absence of evidence, especially from gene expression analyses. Further, the interpretations offered by Liu et al. of their results are not as straightforward as they contend since some of their data can also be viewed as supportive of postnatal oogenesis in reproductive age women.     

Absence of the Δccr5 mutation in indigenous populations of the Brazilian Amazon

Carriers of the deltaccr5 allele, which contains a deletion of 32 bases in relation to the normal allele of the beta-chemokine receptor gene (CCR5), have increased resistance to HIV-1 infection. The higher frequency of this mutation in Europeans than in Blacks and Asians, has generated interest in determining its distribution in other populations. The population of this study involved 300 Amerindians from four Brazilian Amazon tribes (Tikuna, Baniwa, Kashinawa, and Kanamari). All of the individuals were homozygous for the normal allele, which corroborates the hypothesis that the deltaccr5 allele has a European origin, and that its occurrence in urban populations in South America is the result of immigration.     

Mutations on the N-Terminal Edge of the DELSEED Loop in either the α or β Subunit of the Mitochondrial F1-ATPase Enhance ATP Hydrolysis in the Absence of the Central γ Rotor

F₁-ATPase is a rotary molecular machine with a subunit stoichiometry of α₃β₃γ₁δ₁ε₁. It has a robust ATP-hydrolyzing activity due to effective cooperativity between the three catalytic sites. It is believed that the central γ rotor dictates the sequential conformational changes to the catalytic sites in the α₃β₃ core to achieve cooperativity. However, recent studies of the thermophilic Bacillus PS3 F₁-ATPase have suggested that the α₃β₃ core can intrinsically undergo unidirectional cooperative catalysis (T. Uchihashi et al., Science 333:755-758, 2011). The mechanism of this γ-independent ATP-hydrolyzing mode is unclear. Here, a unique genetic screen allowed us to identify specific mutations in the α and β subunits that stimulate ATP hydrolysis by the mitochondrial F₁-ATPase in the absence of γ. We found that the F446I mutation in the α subunit and G419D mutation in the β subunit suppress cell death by the loss of mitochondrial DNA (ρ^o) in a Kluyveromyces lactis mutant lacking γ. In organello ATPase assays showed that the mutant but not the wild-type γ-less F₁ complexes retained 21.7 to 44.6% of the native F₁-ATPase activity. The γ-less F₁ subcomplex was assembled but was structurally and functionally labile in vitro. Phe446 in the α subunit and Gly419 in the β subunit are located on the N-terminal edge of the DELSEED loops in both subunits. Mutations in these two sites likely enhance the transmission of catalytically required conformational changes to an adjacent α or β subunit, thereby allowing robust ATP hydrolysis and cell survival under ρ^o conditions. This work may help our understanding of the structural elements required for ATP hydrolysis by the α₃β₃ subcomplex.     

Stabilization of the GluCl Ligand-Gated Ion Channel in the Presence and?Absence of Ivermectin

Improving our understanding of the mechanisms and effects of anesthetics is a critically important part of neuroscience. The currently dominant theory is that anesthetics and similar molecules act by binding to Cys-loop receptors in the postsynaptic terminal of nerve cells and potentiate or inhibit their function. Although structures for some of the most important mammalian channels have still not been determined, a number of important results have been derived from work on homologous cationic channels in bacteria. However, partly due to the lack of a nervous system in bacteria, there are a number of questions about how these results relate to higher organisms. The recent determination of a structure of the eukaryotic chloride channel, GluCl, is an important step toward accurate modeling of mammalian channels, because it is more similar in function to human Cys-loop receptors such as GABA_AR or GlyR. One potential issue with using GluCl to model other receptors is the presence of the large ligand ivermectin (IVM) positioned between all five subunits. Here, we have performed a series of microsecond molecular simulations to study how the dynamics and structure of GluCl change in the presence versus absence of IVM. When the ligand is removed, subunits move at least 2 Å closer to each other compared to simulations with IVM bound. In addition, the pore radius shrinks to 1.2 Å, all of which appears to support a model where IVM binding between subunits stabilizes an open state, and that the relaxed nonIVM conformations might be suitable for modeling other channels. Interestingly, the presence of IVM also has an effect on the structure of the important loop C located at the neurotransmitter-binding pocket, which might help shed light on its partial agonist behavior.     

Absence of Nepotism in Worker–Queen Care in Polygynous Colonies of the Ant Ectatomma tuberculatum

The question of the occurrence of nepotism in insect societies is central to inclusive fitness theory. Here we investigated the existence of nepotism in the facultative polygynous ant Ectatomma tuberculatum because various characteristics of this species may have favored the evolution of nepotistic behavior toward queens. We thus studied worker–queen care toward their mother queen vs. an unrelated unfamiliar queen, to determine if workers cared preferentially for their mother. Although we tried to facilitate the expression of nepotistic behaviors, we did not detect significant nepotism confirming the general trend of an absence of nepotism in social insects. We discuss about the specific causes that can explain the absence of nepotism in E. tuberculatum regarding the particular social organization of this species and its ecological dominance in the mosaic of arboreal ants.     

Does Melanin Turnover Occur in the Eyes of Adult Vertebrates?

This paper is a review of what is known about the turnover of melanin in iris, choroid, and retinal pigment epithelium (RPE) of the adult vertebrate eye. Differences in size and structure of choroideal and retinal pigment epithelial melanin granules are shown by electron micrographs. The classical stages of melanin synthesis, including the premelanosome, are shown in the RPE of adult hamsters that had been exposed to intense light. Degradation or synthesis of melanin also seem to occur in the melanocytes of the choroid in these animals. It is postulated that all three pigmented eye tissues (iris, RPE, and choroid) of adult vertebrates form melanin granules in vivo. However, nothing is known about the amount of this turnover.     

“Robin Hood” of Techno-Turkey or Organ Trafficking in the State of Ethical Beings

Dr S. is a famous transplant surgeon in the Middle East. He operates "underground" on wealthy patients in different countries, from Israel to Turkey to Russia. The media refer to him as the "Organ Mafia doctor," and patients diagnosed with renal failure speak of him sardonically as "Robin Hood," acknowledging that he takes organs from the poor to give to the rich. But ethical issues of organ trafficking are not limited to marginal private clinics and "Mafia" doctors. All-living related organ transplants in Turkey involve similar ethical dilemmas: many related or nonrelated organ recipients pay their donors, and demand continues to rise. This paper explores practices in state and university hospitals and the ethical dilemmas doctors encounter to understand where and how judicial, cultural, and social categories of "human rights" and "crime" are constructed in our high-tech world.     

To self or not to self? Absence of mate choice despite costly outcrossing in the fungus Podospora anserina

Fungi have a large potential for flexibility in their mode of sexual reproduction, resulting in mating systems ranging from haploid selfing to outcrossing. However, we know little about which mating strategies are used in nature, and why, even in well-studied model organisms. Here, we explored the fitness consequences of alternative mating strategies in the ascomycete fungus Podospora anserina. We measured and compared fitness proxies of nine genotypes in either diploid selfing or outcrossing events, over two generations, and with or without environmental stress. We showed that fitness was consistently lower in outcrossing events, irrespective of the environment. The cost of outcrossing was partly attributed to non-self recognition genes with pleiotropic effects on fertility. We then predicted that when presented with options to either self or outcross, individuals would perform mate choice in favour of the reproductive strategy that yields higher fitness. Contrary to our prediction, individuals did not seem to avoid outcrossing when a choice was offered, in spite of the fitness cost incurred. Our results suggest that, although functionally diploid, P. anserina does not benefit from outcrossing in most cases. We outline different explanations for the apparent lack of mate choice in face of high fitness costs associated with outcrossing, including a new perspective on the pleiotropic effect of non-self recognition genes.