Par6B and atypical PKC regulate mitotic spindle orientation during epithelial morphogenesis

Area of Science:

• Cell Biology
• Developmental Biology
• Epithelial Biology

Background:

• Cdc42 is essential for cell polarity and epithelial morphogenesis.
• Previous studies showed Cdc42 regulates mitotic spindle orientation in developing epithelial structures.
• The downstream effectors of Cdc42 in this process were yet to be fully elucidated.

Purpose of the Study:

• To investigate the downstream effectors of Cdc42 in regulating epithelial morphogenesis.
• To determine the roles of Par6B and atypical protein kinase C (aPKC) in Cdc42-mediated processes.
• To understand the mechanism of Par6B and aPKC action in Caco-2 cell cyst formation.

Main Methods:

• Utilized a three-dimensional matrigel model with Caco-2 cells to form polarized cysts.
• Employed depletion and inhibition strategies for Par6B and aPKC.
• Analyzed mitotic spindle orientation, apical surface positioning, and cyst morphology.
• Investigated protein localization and degradation pathways.

Main Results:

• Depletion or inhibition of Par6B or aPKC mimicked Cdc42 loss, causing spindle misorientation and aberrant cyst formation.
• Par6B recruits aPKC to the apical surface, while aPKC protects Par6B from degradation.
• aPKC inhibition led to apoptosis and reduced cyst size and number, indicating distinct roles in cell survival and positioning.

Conclusions:

• Par6B and aPKC are critical downstream effectors of Cdc42 in controlling mitotic spindle orientation in polarized epithelia.
• aPKC plays a dual role, regulating both cell survival and apical positioning during morphogenesis.
• These findings elucidate a key molecular pathway governing epithelial development and tissue organization.