Effect of taxol and okadaic acid on microtubule dynamics in thimerosal‐arrested primary mouse oocytes: a confocal study

Abstract

A pulse of thimerosal (TMS), a sulfhydryl reagent, induces an instantaneous, complete and long-lasting microtubule interphasic network disassembly in mouse primary oocytes, correlated with the irreversible inhibition of meiosis reinitiation This inhibition is bypassed by dithiothreitol (DTT) while thiosalicylic acid, an analog of TMS, does induce neither microtubules depolymerisation nor inhibition of reinitiation and resumption of meiosis. This strongly suggests that the dramatic and pleiotropic inhibitory effect of TMS is specifically related to its sulfhydryl group oxidising activity of critical molecules among which tubulin. In contrast to DTT, okadaic acid (OA), known to bypass the inhibitory effect of drugs interfering with protein kinase activities, induces a late chromatin condensation and GVBD in TMS-pulsed oocytes as compared to the control situation, with no significant concomitant microtubule assembly. These cytological features are suggested to be indirectly induced by a late MAPK activation and confirm that a very early thiol oxidation induced by TMS exerts a much more dramatic effect on resumption of meiosis than any pharmacological manipulation of protein kinase activities leading to activation of MPF. Finally, taxol was shown to promote tubulin polymerisation even when microtubules were irreversibly disassembled by thiol oxidation but fails to restore the ability to undergo maturation.

Effects of Thimerosal on NGF Signal Transduction and Cell Death in Neuroblastoma Cells

“…The studies cited above identified a number of molecular targets for thimerosal, have including micronuclei induction, disturbances of intracellular calcium, and inhibition of glutathione content (Ueha-Ishibashi et al, 2005a;2004b;Westphal et al, 2003), but the unique dependence of the developing nervous system on growth factors suggests that the neurotrophins and their receptors represent a possible target for thimerosal. There are a several studies suggesting that thimerosal may alter neurotrophin signaling, including binding of secondary messengers (Vanlingen et al 2001), microtubule assembly (Alexandre et al 2003), and intracellular calcium concentrations (Ueha-Ishibashi et al 2004a). Neurotrophins, especially nerve growth factor (NGF), but also the related neurotrophins, brain-derived growth factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4/5 (NT-4/5), are known to affect the biological behavior of neuronal cells during development, survival and differentiation of the central and peripheral nervous systems (Barde 1989;Thoenen 1991).…”

Nicotine combined with okadaic acid or taxol adversely affects bovine oocyte maturation and subsequent embryo development

“…Okadaic acid induced an approximate twofold increase in the frequency of catastrophic transitions and a threefold decrease in the frequency of rescue transitions (25). For mammalian oocytes, OA could induce the resumption of meiosis, including GVBD and mitosis promoting factor (MPF) activation, and metaphase spindle formation in mice (12,13,26). Taxol is known to promote microtubule assembly by shifting the equilibrium between tubulin dimer and polymer in favor of microtubular formation (14).…”

“…The synergistic effects of nicotine and OA or nicotine and taxol on oocyte maturation and chromatid separation is very complicated. Okadaic acid independently induces premature separation of sister chromatids while regulating oocyte maturation and the transition from metaphase to anaphase in the mouse (12).…”

“…Exposure of mammalian oocytes to OA stimulates oocyte germinal vesicle breakdown (GVBD), resulting in the oocytes not developing beyond metaphase I (MI) and displaying a variety of spindle aberrations (11). Okadaic acid reverses the effect of 6-dimethylaminopurine on p34 cdc2 tyrosine phosphorylation and the inhibitory action of phorbol esters and drugs interfering with protein kinase activities (10,12,13). Taxol promotes microtubule assembly by shifting the equilibrium between tubulin dimer and polymer in favor of microtubule formation (14).…”

“…The cellular target of taxol is the b-tubulin subunit in the polymer (15,16). In mouse oocytes, taxol induces a fast restructuring of the microtubule network (12). Incubation of cells with taxol causes the formation of stable bundles or parallel arrays of microtubules resulting in cellular arrest during mitosis (17).…”