Cell and mechanobiology of Asymmetric Cell Division

PROJECT SUMMARY
Generating cells with different fates, functions and behaviors is critically important for the development and
maintenance of tissues, organs, and multicellular organisms. Cellular diversity can be generated through
Asymmetric Cell Division (ACD). Stem cells utilize ACD to create differentiating sibling cells while
maintaining the stem cell in the process. In addition to the asymmetric partitioning of proteins or RNAs, other
mechanisms such as mechanical cues, sibling cell size asymmetry or organelle asymmetry could
potentially also contribute to binary cell fate decisions.
Here, I propose to use asymmetrically dividing Drosophila neuroblasts, the neural stem cells of the
developing fly central nervous system, to investigate the cell and mechanobiology of ACD in vivo. Recently,
we discovered that Non-muscle Myosin II-dependent cortical flows, induced through both polarity- and
spindle-dependent cues, are implicated in the generation of sibling cell size asymmetry. I will investigate how
cortical flows are induced and modulated with spatiotemporal precision to achieve reproducible sibling cell
size asymmetry. Our recent discovery of Protein Kinase N (PKN), and the Rho GTPase pathway as inducers
of cortical flows will provide molecular entry points. I will also investigate how cell size asymmetry contributes
to cell fate decisions, using RNA sequencing, immunohistochemistry, and long-term live cell imaging in vivo.
A second project encompassed in this research direction is aimed at investigating the molecular
mechanisms and function of molecular centrosome asymmetry, which is manifested in biased microtubule
organizing center (MTOC) activity in interphase. We identified new proteins and mechanisms, such as
Kinesins, Pp4 and dynamic centriolar protein localization in mitosis, regulating centrosome asymmetry.
Centrosome segregation is highly stereotypic in stem cells, but whether and how centrosome
asymmetry affects cell fate decisions, remains to be resolved. We will use fly neural stem cells to
investigate the mechanisms and functions of centrosome asymmetry during ACD. I am particularly interested
in investigating whether centrosome asymmetry provides a mechanism for biased cell fate determinant
segregation, either via asymmetric RNA or sister chromatid segregation. I will also investigate whether biased
MTOC activity impacts transcriptional regulation via chromatin organization.
This research program will benefit from several novel and innovative tools, consisting of live cell imaging,
superresolution microscopy, RNA sequencing and acute protein mislocalization and perturbation systems
(nanobody, optogenetics), which my lab implemented to probe cytoskeletal dynamics with high spatial and/or
temporal precision in vivo.
ACD is an evolutionary conserved mechanism and the proposed research program is medically
significant because defects in ACD can cause neurodevelopmental disorders or cancer.

Grant Number: 5R35GM148160-04
NIH Institute/Center: NIH
Principal Investigator: Clemens Cabernard