I am excited about the fundamental processes by which a single cell develops into a multicellular organism with accurately shaped organs. This centuries old-question can be addressed at various scales - molecular, cellular, and tissue, and I am interested in such multi-scale investigation of this problem. One aspect I am particularly excited about is the role of mechanical forces - understanding how cells and tissues deform in space and time and how the generated forces influence cellular decision making.
Below are the specific research problems I have been addressing.
Fluid mechanics in shaping organs
For my postdoc, I chose to investigate the role of fluid mechanics in tissue morphogenesis (the generation of form from the Greek words morphe and genesis). Water is a fundamental molecule and is the basis of life on our planet. During embryonic development besides cells interior, water or fluid is present in the intercellular spaces and cellular/epithelial cavities. Whether water present in the cellular cavities can instruct cells to adopt different fates, morphologies, and sizes has remained vastly unexplored. Recent studies from Sean Megason, Jean-Léon Maître, Takashi Hiiragi, Sean Sun, Xavier Trepat, and a few other labs have demonstrated a critical role of hydrostatic pressure in cellular decision making and in controlling organ size. However, we have just started to scratch the surface.
I am addressing how hydrostatic pressure and fluid flow sculpt and design the inner ear during embryonic development. We know pressure defects in the ear can lead to deafness or problems with balance. To understand this problem, I am using zebrafish or Danio rerio as a model system. Zebrafish is an excellent choice as their embryos are optically transparent and lack outer and middle ears, therefore making inner ear accessible and live-imaging effective.
Inner ear (oval shaped structure) at 24 hours post fertilisation. Cell membranes are shown in green and fluid in the intercellular spaces and cavities is shown in magenta. The image was acquired using Zeiss 980 confocal microscope.
Chugh M, Munjal A, Megason SG. (2022). “Hydrostatic pressure as a driver of cell and tissue morphogenesis”, Sem. Cell Dev. Biology, in press.
Plant cell division plane alignment
Plant development and morphology rely on the accurate insertion of new cell walls during cytokinesis. During my PhD, I addressed this poorly understood question-how do plants accurately and faithfully align their cell division plane after mitosis? Two kinesin class-12 members, phragmoplast orienting kinesin 1 (POK1) and POK2, were just discovered to be involved in the process, but how these molecular machines work themselves and in the process was not known. I used in vivo and single-molecule in vitro measurements to determine how Arabidopsis thaliana POK2 and POK1 motors function mechanically. I found that POK2 is a very weak (0.3pN), on average plus-end-directed, moderately fast kinesin (430 nm/s). Interestingly, both motors switch between processive and diffusive modes characterised by an exclusive-state mean-squared-displacement analysis. By integrating this single-molecule biophysical characterisation of the POK1 and POK2 motors with in planta localisation microscopy, I proposed a pushing-force model. The model posits that POK motors at the cell membrane push against the peripheral microtubules of the phragmoplast for its guidance.
Proposed pushing-force model by POK motors at the cell membrane for guidance of peripheral microtubules and thus, alignment of the cell division plane.
Chugh, M., Reißner, M., Bugiel, M., Lipka, E., Herrmann, A., Roy, B., Müller, S. and Schäffer, E., (2018). Phragmoplast orienting kinesin 2 is a weak motor switching between processive and diffusive modes. Biophysical journal, 115(2), 375-385.
Livanos, P., Chugh, M., & Müller, S. (2017). Analysis of phragmoplast kinetics during plant cytokinesis. Plant Protein Secretion, 137-150.
Blood stem cells and niche regulation
My interest in developmental biology and cell biology is instilled by Lolitika Mandal. I worked as a student researcher and as a master student in her laboratory. I undertook several independent projects in understanding how a niche maintains itself, which is indispensable for stem cell function and homeostasis. I investigated this by exploiting Drosophila or fruit fly haematopoiesis (blood generation) as a model system. I identified a scaffold provided by the somatic musculature to the haematopoietic niche within the larval haematopoietic organ or the lymph gland. Currently, this scaffold geometry is used as an assay in the Mandal lab to ensure the functionality of the niche. During my master's thesis, I uncovered the molecular role of Delta-Notch signalling in the decision making by bipotent blood progenitor cells in larval haematopoiesis. In a team, I also identified elusive haematopoietic stem cells (HSCs) during early larval haematopoiesis.
Proposed molecular mechanism of HSCs maintenance by Dpp/BMP signalling instructed by the niche during early larval haematopiesis.
Dey, N. S., Ramesh, P., Chugh, M., Mandal, S., & Mandal, L. (2016). Dpp dependent Hematopoietic stem cells give rise to Hh dependent blood progenitors in larval lymph gland of Drosophila. Elife, 5, e18295.