A 12-Crown-4 Ether Containing Dipeptide Boc-12-Crown-4-<Emphasis Type="SmallCaps">l</Emphasis>-DOPA-Gly-OMe Induces Cell Cycle Arrest and Apoptosis in Rat Eggs Cultured In Vitro

The study was designed to investigate whether crown ether containing dipeptide Boc-12-crown-4-l-DOPA-Gly-OMe has potential to induce meiotic cell cycle arrest and apoptosis in rat eggs cultured in vitro. The immature female rats were subjected to superovulation induction protocol and ovulated eggs were collected from ampulla of the fallopian tube. Ovulated eggs arrested at metaphase-II (M-II) stage of meiotic cell cycle were cultured in media-199 with or without various concentrations (0.0, 0.025, 0.050, 0.10, and 0.20 mM) of dipeptide for 3 h in vitro. Morphological apoptotic changes, hydrogen peroxide (H₂O₂) concentration, cytochrome c level, caspase-3 level as well as activity and DNA fragmentation were analysed in eggs cultured in vitro. Culture of M-II arrested eggs in plain medium for 3 h in vitro induced meiotic exit from M-II arrest in majority of eggs as evidenced by initiation of extrusion of second polar body (II PB). The dipeptide induced maintenance of M-II arrest and morphological apoptotic features in a concentration-dependent manner prior to degeneration. The dipeptide-induced morphological features were associated with increased H₂O₂ and cytochrome c levels in treated eggs. The increased cytochrome c induced caspase-3 level and activity and thereby DNA fragmentation as evidenced by DAB positive staining in treated eggs. Our results suggest that dipeptide Boc-12-C-4-l-DOPA-Gly-OMe induces cell cycle arrest at M-II stage and apoptosis in rat eggs cultured in vitro.     

Characteristics of Electronegative Plasma Sheath with <Emphasis Type="Italic">q</Emphasis>-Nonextensive Electron Distribution

The characteristics of sheath in a plasma system containing q-nonextensive electrons, cold fluid ions, and Boltzmann-distributed negative ions are investigated. A modified Bohm sheath criterion is derived by using the Sagdeev pseudopotential technique. It is found that the proposed Bohm velocity depends on the degree of nonextensivity (q), negative ion temperature to nonextensive electron temperature ratio (σ), and negative ion density (B). Using the modified Bohm sheath criterion, the sheath characteristics, such as the spatial distribution of the potential, positive ion velocity, and density profile, have been numerically investigated, which clearly shows the effect of negative ions, as well as the nonextensive distribution of electrons. It is found that, as the nonextensivity parameter and the electronegativity increases, the electrostatic sheath potential increases sharply and the sheath width decreases.     

Temperature-mediated switching of protectant-denaturant behavior of trimethylamine-N-oxide and consequences on protein stability from a replica exchange molecular dynamics simulation study

The detailed mechanism of protein folding–unfolding processes with the aid of osmolytes has been a leading topic of discussion over many decades. We have used replica-exchange molecular dynamics simulation to propose the molecular mechanism of interaction of a 20-residue mini-protein with urea and trimethylamine N-oxide (TMAO) that act as denaturing and protecting osmolyte, respectively, in binary osmolyte solutions. Urea is found to exert its action by interacting directly with the protein residues. Temperature tolerance of TMAO’s action is particularly emphasised in this study. At lower range of temperature, TMAO acts as a successful protein protectant. Interestingly, the study discloses the tendency of TMAO molecules to prefer self-association at the protein surface at elevated temperature. A greater number of TMAO molecules in the protein hydration shell at higher temperature is also observed. Dihedral angle principal component analysis and free energy landscape plots sampled all possible conformations adopted by the protein that reveal highly folded behaviour of the protein in pure water and binary TMAO solutions and highly unfolded behaviour in presence of urea.     

Reactive oxygen and nitrogen species during meiotic resumption from diplotene arrest in mammalian oocytes

Mammalian ovary is metabolically active organ and generates by‐products such as reactive oxygen species (ROS) and reactive nitrogen species (RNS) on an extraordinary scale. Both follicular somatic cells as well as oocyte generate ROS and RNS synchronously and their effects are neutralized by intricate array of antioxidants. ROS such as hydrogen peroxide (H₂O₂) and RNS such as nitric oxide (NO) act as signaling molecules and modulate various aspects of oocyte physiology including meiotic cell cycle arrest and resumption. Generation of intraoocyte H₂O₂ can induce meiotic resumption from diplotene arrest probably by the activation of adenosine monophosphate (AMP)‐activated protein kinase A (PRKA)—or Ca²⁺‐mediated pathway. However, reduced intraoocyte NO level may inactivate guanylyl cyclase‐mediated pathway that results in the reduced production of cyclic 3′,5′‐guanosine monophosphate (cGMP). The reduced level of cGMP results in the activation of cyclic 3′,5′‐adenosine monophosphate (cAMP)‐phosphodiesterase 3A (PDE3A), which hydrolyses cAMP. The reduced intraoocyte cAMP results in the activation of maturation promoting factor (MPF) that finally induces meiotic resumption. Thus, a transient increase of intraoocyte H₂O₂ level and decrease of NO level may signal meiotic resumption from diplotene arrest in mammalian oocytes. J. Cell. Biochem. 111: 521–528, 2010. © 2010 Wiley‐Liss, Inc.