Quantitative analysis of protein dynamics during asymmetric cell division

Area of Science:

• Cell Biology
• Developmental Biology
• Genetics

Background:

• Asymmetric protein localization is crucial for cell fate determination in dividing cells.
• Numb and Pon proteins are key fate determinants in Drosophila sensory organ precursor (SOP) cells, requiring asymmetric segregation for proper cell fate regulation.
• Previous models suggested lateral transport along the cell cortex for Numb and Pon localization.

Purpose of the Study:

• To investigate the dynamics of Numb and Pon localization during SOP cell division.
• To elucidate the mechanism underlying the asymmetric distribution of Numb and Pon.
• To identify the roles of aPKC and Lgl in regulating Numb and Pon localization.

Main Methods:

• Quantitative live imaging of GFP-tagged Pon and Numb-GFP.
• Fluorescence recovery after photobleaching (FRAP) to analyze protein dynamics.
• Genetic manipulation of aPKC and Lgl activity.

Main Results:

• Numb and Pon exhibit rapid exchange between the cytoplasm and cell cortex.
• Asymmetric localization is achieved through preferential recruitment from the cytoplasm.
• Active aPKC inhibits Pon membrane recruitment, a defect rescued by nonphosphorylatable Lgl, identifying Lgl as a key aPKC target.

Conclusions:

• Asymmetric localization of Numb and Pon is driven by preferential cytoplasmic recruitment, not solely lateral transport.
• aPKC and Lgl cooperatively establish an asymmetrically distributed high-affinity binding site for these determinants.
• This mechanism ensures precise cell fate determination during mitosis in Drosophila SOPs.