Zea mays Meiotic Spindle Ultrastructure Reveals Kinetochore-Microtubule Interface and Embedded Membrane Components

Area of Science:

• Cell Biology
• Cytogenetics
• Structural Biology

Background:

• Cell division relies on spindle apparatus for accurate chromosome segregation.
• Spindle structure is critical; errors lead to aneuploidy, disease, and infertility.
• Zea mays (maize) is a vital crop and model system, yet its meiotic spindle structure remains uncharacterized.

Purpose of the Study:

• To elucidate the three-dimensional ultrastructure of the Zea mays meiotic spindle at nanometer resolution.
• To identify and characterize key components and unique features of the maize meiotic spindle.
• To compare maize spindle structures with those of other organisms.

Main Methods:

• Electron tomography (ET) was employed to capture high-resolution 3D images of the maize meiotic spindle.
• Reconstruction and modeling techniques were used to visualize microtubules, kinetochores, and associated structures.
• Immunostaining and live fluorescence microscopy confirmed the modeled structures.

Main Results:

• Maize meiotic spindles feature 8-18 kinetochore microtubules (kMTs) per kinetochore.
• Unique structures observed include small vesicles (~37 nm) and large membrane channels (~5 µm long, 800 nm wide) containing microtubules, positive for ER markers.
• A perinuclear microtubule ring with a cross-hatch arrangement and nuclear grooves with transnuclear microtubules was identified.

Conclusions:

• Zea mays meiotic spindles share similarities with animal spindles, including kMT number and transnuclear microtubules.
• Plant-specific features include Golgi-derived vesicles for cell plate formation and internal ER membrane channels.
• The perinuclear microtubule ring aids spindle assembly, and maize kinetochores exhibit a distinct 'ball in cup' morphology.