Fertilizable mammalian oocytes are arrested at the second meiotic metaphase (mII) by the cyclinB-Cdc2 heterodimer, maturation promoting factor (MPF). MPF is stabilized via the activity of an unidentified cytostatic factor (CSF), thereby suspending meiotic progression until fertilization. We here present evidence that a conserved 71 kDa mammalian orthologue of Xenopus XErp1/Emi2, which we term endogenous meiotic inhibitor 2 (Emi2) is an essential CSF component. Depletion in situ of Emi2 by RNA interference elicited precocious meiotic exit in maturing mouse oocytes. Reduction of Emi2 released mature mII oocytes from cytostatic arrest, frequently inducing cytodegeneration. Mos levels autonomously declined to undetectable levels in mII oocytes. Recombinant Emi2 reduced the propensity of mII oocytes to exit meiosis in response to activating stimuli. Emi2 and Cdc20 proteins mutually interact and Cdc20 ablation negated the ability of Emi2 removal to induce metaphase release. Consistent with this, Cdc20 removal prevented parthenogenetic or sperm-induced meiotic exit. These studies show in intact oocytes that the interaction of Emi2 with Cdc20 links activating stimuli to meiotic resumption at fertilization and during parthenogenesis in mammals.

Excitatory neurons are preferentially impaired in early Alzheimer’s disease but the pathways contributing to their relative vulnerability remain largely unknown. Here we report that pathological tau accumulation takes place predominantly in excitatory neurons compared to inhibitory neurons, not only in the entorhinal cortex, a brain region affected in early Alzheimer’s disease, but also in areas affected later by the disease. By analyzing RNA transcripts from single-nucleus RNA datasets, we identified a specific tau homeostasis signature of genes differentially expressed in excitatory compared to inhibitory neurons. One of the genes, BCL2 associated athanogene 3 BAG3 , a facilitator of autophagy, was identified as a hub or master regulator, gene. We verified that reducing BAG3 levels in primary neurons exacerbated pathological tau accumulation whereas overexpression attenuated it. These results support the conclusion that tau homeostasis underlies the cellular and regional vulnerability of excitatory neurons to tau pathology.

Oscillatory rises in intracellular Ca2+ concentration ([Ca2+]i) are the pivotal signal in the fertilization of mammalian eggs. The spatiotemporal dynamics of [Ca2+]i rises in mouse eggs subjected to intracytoplasmic sperm injection (ICSI) were analysed by Ca2+ imaging and compared with those subjected to in-vitro fertilization (IVF). The first Ca2+ transient occurred 15-30 min after ICSI in most eggs, and was followed by Ca2+ oscillations which lasted for at least 6 h at intervals of approximately 10 min. The pattern of Ca2+ oscillations, an initial relatively larger Ca2+ transient followed by smaller Ca2+ transients, was similar to that at fertilization. Confocal Ca2+ imaging during early Ca2+ transients showed that, in fertilized eggs, [Ca2+]i increased in a wave which started from the sperm attachment site and propagated across the egg cytoplasm. In eggs subjected to ICSI, [Ca2+]i increased gradually and then a Ca2+ spike was generated when [Ca2+]i reached a certain level. The [Ca2+]i rise occurred in the whole egg, associated with neither a wave nor significant heterogeneity between the cortical and central regions. It is suggested that cytosolic factor(s) may leak from the injected spermatozoon, diffuse slowly in the egg cytoplasm, and then cause a synchronous Ca2+ release from intracellular Ca2+ stores.

Background and Purpose-Status epilepticus and cerebral ischemia stimulate persistent neurogenesis in the adult brain, but both conditions cause neuronal damage. We determined whether spreading depression, a common epiphenomenon of these conditions, stimulates persistent neurogenesis. Methods-We analyzed the effect of KCl-induced spreading depression on persistent neurogenesis and the spatio-temporal distribution of cells exhibiting immunohistochemical markers for divided and early committed neurons (new neurons) in the adult rat brain. Results-After induction of spreading depression for 48 hours, the density of mitotic cells, divided cells, and new neurons in the subventricular zone increased at days 1 to 3, days 3 to 6, and day 6, respectively (PϽ0.05). The divided cell density in the rostral migratory stream and the stream size increased at day 12 (PϽ0.001). Vehicle (saline) infusion or induction of spreading depression for 4 hours only did not increase the divided cell density, but the latter increased new neuron density in the subventricular zone (PϽ0.001). Double-labeled new neuron-like cells also appeared in the caudate putamen or cortex in ectopic fashion at day 3, with dramatic increases at days 6 and 12. Administration of the NMDA receptor antagonist, MK-801, which inhibits the propagation of spreading depression, abolished the increase in new neurons in the subventricular zone and the appearance of ectopic new neuron-like cells after 48-hour KCl infusion. There was no neuronal damage, as evidenced by mature neuron density, neurite density, and apoptotic cell appearance after spreading depression for 48 hours. Conclusions-Spreading

Mammalian metaphase II (mII) exit and embryogenesis are induced at fertilisation by a signal thought to come from the sperm protein, phospholipase C-zeta (PLCZ1). Meiotic progression can also be triggered without sperm, as in parthenogenesis, although the classic mouse in vivo parthenogenetic model, LT/Sv, fails in meiosis I owing to an unknown molecular etiology. Here, we dissect PLCZ1 specificity and function in vivo and address its ability to interfere with maternal meiotic exit. Wild-type mouse Plcz1 expression was restricted to post-pubertal testes and the brains of both sexes, with region-specifying elements mapping to a 4.1 kb Plcz1 promoter fragment. When broad ectopic PLCZ1 expression was forced in independent transgenic lines, they initially appeared healthy. Their oocytes underwent unperturbed meiotic maturation to mII but subsequently exhibited autonomous intracellular free calcium oscillations, second polar body extrusion, pronucleus formation and parthenogenetic development. Transfer of transgenic cumulus cell nuclei into wild-type oocytes induced activation and development, demonstrating a direct effect of PLCZ1 analogous to fertilisation. Whereas Plcz1 transgenic males remained largely asymptomatic, females developed abdominal swellings caused by benign ovarian teratomas that were under-represented for paternally-and placentally-expressed transcripts. Plcz1 was not overexpressed in the ovaries of LT/Sv or in human germline ovarian tumours. The narrow spectrum of PLCZ1 activity indicates that it is modulated by tissue-restricted accessory factors. This work characterises a novel model in which parthenogenesis and tumourigenesis follow full meiotic maturation and are linked to fertilisation by PLCZ1.