If and how cell intrinsic biophysical parameters, such as cell stiffness, intracellular
pressure or active cortex tension affect cell shape changes and subsequently cell fate
decisions and cell behavior is an open question in cell and developmental biology. An
ideal system to address this question are Drosophila neuroblasts, the precursors of the
fly’s central nervous system. These neural stem cells divide very stereotypically in a
physical and molecular asymmetric manner, always generating a self-renewed
neuroblast and a differentiating ganglion mother cell (GMC) or an intermediate neural
progenitor (INP). For instance the self-renewed neuroblast is ~2 times larger than the
GMC. Also, cell fate determinants segregate asymmetrically; either to the self-renewed
neuroblast or the differentiating GMC/INP. Although all neuroblast sublineages
originate from the same precursor cells and show almost the same asymmetric marker
segregation profile, they differ in cell cycle time, fate and behavior. Thus, Drosophila
neuroblasts are ideally suited to address the question how mechanical forces influence
cell shape changes and concomitantly, cell behavior and fate.
In order to address this question, we first need to carefully measure and quantify cell
biological and biophysical parameters of wild type neuroblast sublineages. To this end,
we will use advanced live imaging techniques combined with atomic force microscopy,
active cortex tension measurements and Particle Image Velocimetry (PIV). These
measurements will also be used to characterize the cell biological and biophysical
parameters of several mutants affecting neuroblast size asymmetry, thereby allowing
us to learn how mechanistic properties, and changes thereof, affect sibling cell size,
cell behavior and fate.
Interestingly, many mutants affecting physical asymmetry also cause Drosophila brain
tumors, in some instances in particular sublineages only. Thus, our measurements
will allow us to correlate cell size asymmetry, molecular asymmetry and tumor
inducing capacity and eventually test the contribution of altered cell mechanics on
tumor formation.
We propose the following aims:
Aim 1: Comparison of the cell biological (cell cycle, cell size) and mechanical (stiffness,
intracellular pressure, active cortex tension) properties between embryonic, central
brain type I and type II neuroblasts.
Aim 2: Aim 2: Measurement of cell biological and mechanical properties of tumor
suppressor mutants in different neuroblast subtypes.
Aim 3: Aim 3: Assessing the tumor-inducing capacity of neuroblasts defective for
physical asymmetry.