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H Alexandre1, V Delsinne, J-J Goval
1Université de Mons-Hainaut, Faculté de Médecine-Pharmacie, Mons, Belgium. henri.alexandre@umh.ac.be
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.
Insights
Thimerosal (TMS) rapidly disassembles oocyte microtubules and halts meiosis by oxidizing thiols. This inhibition is specific to TMS
Area of Science:
- Cell Biology
- Developmental Biology
- Reproductive Biology
Background:
- Microtubules are essential for cell division and oocyte maturation.
- Meiosis reinitiation in oocytes is a complex process regulated by various signaling pathways.
- Thimerosal (TMS) is a mercury-containing compound known to interact with sulfhydryl groups.
Purpose of the Study:
- To investigate the mechanism by which thimerosal (TMS) inhibits meiotic progression in mouse oocytes.
- To determine if TMS's effect is related to its sulfhydryl-oxidizing activity.
- To compare the effects of TMS with other agents affecting microtubule dynamics and signaling pathways.
Main Methods:
- Treatment of mouse primary oocytes with thimerosal (TMS) and its analogs.
- Assessment of microtubule network integrity using immunofluorescence microscopy.
- Evaluation of meiotic progression, including chromatin condensation and germinal vesicle breakdown (GVBD).
- Use of dithiothreitol (DTT) and okadaic acid (OA) to probe specific molecular mechanisms.
Main Results:
- A single pulse of TMS caused rapid and irreversible microtubule disassembly and blocked meiotic reinitiation.
- Dithiothreitol (DTT) could bypass the inhibitory effects of TMS, while thiosalicylic acid had no effect.
- Okadaic acid (OA) induced late maturation events in TMS-treated oocytes, suggesting TMS acts upstream of protein kinase pathways.
- Taxol could not restore maturation in TMS-treated oocytes despite promoting tubulin polymerization.
Conclusions:
- The inhibitory effect of TMS on oocyte meiosis is primarily due to its specific sulfhydryl group oxidizing activity, likely targeting tubulin.
- Early thiol oxidation by TMS has a more profound impact on meiotic resumption than later signaling events.
- Microtubule integrity is critical for timely meiotic progression, and its disruption by TMS has downstream consequences on maturation.
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