Cellular life cannot be sustained and propagated without temporal and spatial organization. Even bacteria, once mistakenly perceived as tiny jumbles of molecules, rely on temporal and spatial organization for many essential processes. In recent years, we have come to realize that bacteria are polarized, possess a cytoskeleton, order their chromosomes in space, localize proteins, and depend critically on this surprisingly exquisite cellular organization. Despite the recent surge of information about bacterial cell biology, our knowledge is still at an early stage and the most fundamental questions remain to be solved, providing unique opportunities to make new and exciting discoveries in this emerging discipline.
Our laboratory addresses the molecular mechanisms involved in the internal organization of bacteria at several levels, from its origin, maintenance and replication in time and space to its function in cellular physiology and morphogenesis. We used two primary model systems: Escherichia coli and Caulobacter crescentus, each having distinct advantages. On one hand, there is a wealth of knowledge on E. coli and studies are facilitated by the availability of large collections of strains, tools and databases. On the other hand, the highly polarized dimorphic Caulobacter crescentus provides a unique set of strengths for addressing questions pertinent to positional and temporal information. Cellular asymmetry is morphologically apparent in C. crescentus by the presence of polar appendages (e.g., stalk, pili and flagellum), and by the obligatory asymmetric division that yields daughter cells of different size, fate and morphology. Populations of C. crescentus cells can be easily synchronized with respect to the cell cycle, providing a means to follow events during the cell cycle. This bacterium also displays a sophisticated morphology and it possesses all three major types of cytoskeletal elements, MreB (actin homolog), FtsZ (tubulin homolog) and crescentin (intermediate filament-like protein).
For our studies, we use an arsenal of genetic, biochemical, bioinformatic and cell imaging tools. A large part of our current strategy is to improve the inventory of components involved in cellular organization, characterize the function and interplay of known components, evolve our work into quantitative studies and computational modeling, and develop methodology to generate new hypotheses and avenues of research.
Cellular polarization and the cell cycle
One of our major goals is to uncover the molecular principles that govern the cell cycle and the acquisition of cell polarity, which are intertwined. Chromosome segregation and cell division rely on localization and interaction of proteins at the cell poles. Similarly, the coordination of cell cycle events depends on signal transduction proteins whose polar localization changes during the cell cycle. We investigate the mechanisms underlying these processes. Additionally, we study the genetic circuitry that integrates, in time and space, cell growth, chromosome segregation, and cell division.
Cell morphogenesis and the cytoskeleton
Bacteria possess defined shapes and sizes that are genetically encoded. This is achieved by temporal and spatial regulation of cell growth and division. The cytoskeleton plays a central role in this regulation, primarily by affecting cell wall biogenesis. How this is done is not well understood and is an active area of research in our laboratory. In this context, we are also studying the structure, metabolism and regulation of the peptidoglycan, which is an essential component of the bacterial cell wall and a prime target for antibiotics. Our goal is to understand at the molecular level how homeostasis of cell size and shape can be achieved.
RNA molecules are involved in many critical cellular functions ranging from transcription and translation (mRNA) to regulation (e.g., small, non-coding RNAs). So far, most RNA studies have been biochemical and in vitro, or genetic and on cell populations. We are developing cell biological approaches to study RNA biology at the single cell level. In the process, we recently discovered that some messenger RNAs accumulate near their sites of transcription. The mechanisms and functional relevance of this localization are currently under study.