An actin-dependent spindle position checkpoint ensures the asymmetric division in mouse oocytes

Cytoskeletal symmetry breaking in animal cells

Symmetry breaking is a crucial step in structure formation and function of all cells, necessary for cell movement, cell division, and polarity establishment. Although the mechanisms of symmetry breaking are diverse, they often share common characteristics. Here we review examples of nematic, polar, and chiral cytoskeletal symmetry breaking in animal cells, and analogous processes in simplified reconstituted systems. We discuss the origins of symmetry breaking, which can arise spontaneously, or involve amplification of a pre-existing external or internal bias to the whole cell level. The underlying mechanisms often involve both chemical and mechanical processes that cooperate to break symmetry in a robust manner, and typically depend on the shape, size, or properties of the cell's boundary.

RAB35 depletion affects spindle formation and actin-based spindle migration in mouse oocyte meiosis

Mammalian oocyte maturation involves a unique asymmetric cell division, in which meiotic spindle formation and actin filament-mediated spindle migration to the oocyte cortex are key processes. Here, we report that the vesicle trafficking regulator, RAB35 GTPase, is involved in regulating cytoskeleton dynamics in mouse oocytes. RAB35 GTPase mainly accumulated at the meiotic spindle periphery and cortex during oocyte meiosis. Depletion of RAB35 by morpholino microinjection led to aberrant polar body extrusion and asymmetric division defects in almost half the treated oocytes. We also found that RAB35 affected SIRT2 and αTAT for tubulin acetylation, which further modulated microtubule stability and meiotic spindle formation. Additionally, we found that RAB35 associated with RHOA in oocytes and modulated the ROCK–cofilin pathway for actin assembly, which further facilitated spindle migration for oocyte asymmetric division. Importantly, microinjection of Myc-Rab35 cRNA into RAB35-depleted oocytes could significantly rescue these defects. In summary, our results suggest that RAB35 GTPase has multiple roles in spindle stability and actin-mediated spindle migration in mouse oocyte meiosis.

Toxic effects and possible mechanisms of hydrogen sulfide and/or ammonia on porcine oocyte maturation in vitro

Previous studies suggest that hydrogen sulfide (H2S) and ammonia (NH3) are two major air pollutants which can cause damage to porcine health. However, the mechanisms underlying toxic effects of these compounds on porcine oocyte maturation are not clear. To clarify the mechanism, we evaluated the oocyte quality by detecting some events during oocytes maturation. In our study, porcine oocytes were cultured with different concentrations of Na2S and/or NH4Cl in vitro and the rate of the first polar body extrusion decreased significantly. Also, actin filament was seriously disrupted to damage the cytoskeleton which resulted in reduced rate of oocyte maturation. We explored the reactive oxygen species (ROS) generation and found that the ROS level was increased significantly after Na2S treatment but not after NH4Cl treatment. Moreover, early stage apoptosis rate was significantly increased and autophagy protein LC3 B expression level was higher in oocytes treated with Na2S and/or NH4Cl, which might be caused by ROS elevation. Additionally, exposure to Na2S and/or NH4Cl also caused ROS generation and early apoptosis in cumulus cells, which might further affect oocyte maturation in vitro. In summary, our data suggested that exposure to H2S and/or NH3 decreased porcine oocyte maturation in vitro, which might be caused by actin disruption, ROS generation, early apoptosis and autophagy.

The Role of Lymphatic Niches in T Cell Differentiation

Long-term immunity to many viral and bacterial pathogens requires CD8(+) memory T cell development, and the induction of long-lasting CD8(+) memory T cells from a naïve, undifferentiated state is a major goal of vaccine design. Formation of the memory CD8(+) T cell compartment is highly dependent on the early activation cues received by naïve CD8(+) T cells during primary infection. This review aims to highlight the cellularity of various niches within the lymph node and emphasize recent evidence suggesting that distinct types of T cell activation and differentiation occur within different immune contexts in lymphoid organs.

Rab3A, Rab27A, and Rab35 regulate different events during mouse oocyte meiotic maturation and activation

Rab family members play important roles in membrane trafficking, cell growth, and differentiation. Almost all components of the cell endomembrane system, the nucleus, and the plasma membrane are closely related to RAB proteins. In this study, we investigated the distribution and functions of three members of the Rab family, Rab3A, Rab27A, and Rab35, in mouse oocyte meiotic maturation and activation. The three Rab family members showed different localization patterns in oocytes. Microinjection of siRNA, antibody injection, or inhibitor treatment showed that (1) Rab3A regulates peripheral spindle and cortical granule (CG) migration, polarity establishment, and asymmetric division; (2) Rab27A regulates CG exocytosis following MII-stage oocyte activation; and (3) Rab35 plays an important role in spindle organization and morphology maintenance, and thus meiotic nuclear maturation. These results show that Rab proteins play important roles in mouse oocyte meiotic maturation and activation and that different members exert different distinct functions.