Development of surface polarity in mouse eggs

Area of Science:

• Cell Biology
• Developmental Biology
• Reproductive Biology

Background:

• Surface polarity is essential for mammalian oocyte development.
• The distribution of microvilli on the oocyte surface changes during maturation.
• The role of the meiotic spindle in establishing this polarity is not fully understood.

Purpose of the Study:

• To investigate the influence of cytoskeletal elements and the meiotic spindle on mouse oocyte surface polarity.
• To determine the mechanisms underlying the formation of the microvillus-free area.

Main Methods:

• In vitro culture of immature mouse oocytes.
• Inhibition of meiotic maturation using dibutyryl cyclic AMP and chloroquine.
• Treatment with cytoskeletal inhibitors: cytochalasin B and colchicine.
• Microscopic observation of oocyte surface morphology and meiotic spindle localization.

Main Results:

• Mature oocytes exhibit a microvillus-free area adjacent to the meiotic spindle, unlike immature oocytes with uniform microvilli.
• Cortical localization of the meiotic spindle coincides with the formation of the microvillus-free area and subjacent microfilaments.
• Inhibition of maturation or disruption of spindle-cortex interactions (cytochalasin B) prevents microvillus-free area formation.
• Colchicine treatment, despite preventing spindle formation, led to cortical chromosome localization and microvillus-free area development.

Conclusions:

• Meiotic spindle movement to the oocyte cortex is critical for establishing surface polarity.
• The development and maintenance of surface polarity are sensitive to cytochalasin B.
• Cortical localization of meiotic chromosomes, not necessarily the intact spindle, induces the formation of the microvillus-free area.