Dithiothreitol Affects the Fertilization Response in Immature and Maturing Starfish Oocytes

Area of Science:

• Marine Biology
• Developmental Biology
• Cell Biology

Background:

• Immature starfish oocytes are prone to polyspermy due to vitelline layer structure and cortical actin.
• Oocyte maturation, triggered by 1-methyladenine (1-MA), involves actin remodeling and germinal vesicle breakdown (GVBD) for normal fertilization.
• Disulfide-reducing agents like dithiothreitol (DTT) can induce oocyte maturation and GVBD in some starfish species.

Purpose of the Study:

• To investigate the effects of dithiothreitol (DTT) on fertilization response in *Astropecten aranciacus* oocytes.
• To compare DTT's effects with 1-methyladenine (1-MA) in inducing oocyte maturation and fertilization competence.

Main Methods:

• Treatment of immature *Astropecten aranciacus* oocytes with DTT, with or without 1-MA.
• Analysis of fertilization rates, sperm-induced calcium (Ca2+) response, and oocyte morphology (microvilli, cortical granules, F-actin).
• Assessment of germinal vesicle breakdown (GVBD) following DTT treatment.

Main Results:

• Short DTT treatment reduced polyspermic fertilization rates in *A. aranciacus* oocytes.
• DTT altered sperm-induced Ca2+ response by modifying microvilli, cortical granules, and cortical F-actin.
• DTT treatment (70 min) did not induce GVBD, unlike 1-MA, and caused F-actin depolymerization, impairing fertilization and development.

Conclusions:

• DTT affects starfish oocyte fertilization by altering cortical actin and microvilli, reducing polyspermy but also impairing normal fertilization processes.
• DTT-induced F-actin depolymerization is distinct from 1-MA-induced maturation, highlighting different pathways for achieving fertilizable conditions.
• While DTT can mitigate polyspermy, it disrupts essential mechanisms for successful fertilization and subsequent embryonic development in *Astropecten aranciacus*.