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Darryl L. Kropf

Professor of biology

B.S. University of California, Berkeley

Ph.D. University of Colorado Health Sciences Center

Research

References

kropf@bioscience.utah.edu

Darryl Kropf's Lab Page

Research

We study cell and molecular mechanisms of plant development using the brown algae Si lvetia and Ectocarpus , as well as the flowering plant Arabidopsis , as model organisms.  

Our primary interest in Silvetia is to identify the mechanisms by which an embryonic axis is established during the first cell cycle following fertilization.   This polarization is of fundamental importance because the spatial control of all subsequent development processes depends on a properly oriented axis.   The goal is to understand the molecular, cellular and physiological basis of embryonic polarity.   At present, much of our work concerns the cytoskeleton.   Cellular components that are uniformly distributed about the egg must become localized to one region of the cytoplasm during polarization, and this reorganization is mediated by cytoskeletal filaments.   The emerging picture is that a local patch of dynamic F-actin defines one pole of the axis. This F-actin patch serves as a target site for secretion, creating a specialized cortical domain at this pole.   Microtubules emanating from centrosomes are captured by this cortical domain and exert force, which rotates the nucleus and aligns the spindle with the embryonic axis.   Cytokinesis bisects the spindle resulting in an asymmetric division invariantly oriented transverse to the axis.   We are currently investigating molecules and pathways that regulate these cytoskeletal rearrangements, including actin nucleation by the Arp2/3 complex and microtubule regulation by plus-end-tracking proteins.  

Genomic approaches are just beginning in the brown algae and the first genome to be sequenced will be that of Ectocarpus , which will be completed in 2006.   Ectocarpus is being developed as a brown algal model organism because it can be cultured in the lab, has a short life cycle and small genome, and mutants can be easily isolated.   We are therefore expanding our studies of developmental polarity to Ectocarpus to take advantage of molecular, genetic and genomic tools as they become available.

We are also investigating mechanisms that regulate microtubule organization, dynamics and function during plant development.   Higher plant microtubules are organized in strikingly different patterns and serve different functions than they do in most other eukaryotic cells.   Plant cells organize a preprophase band of microtubules that specifies the future division plane, as well as a phragmoplast that deposits the cell plate during cytokinesis.   To understand how plant microtubule arrays are regulated, we are investigating the EB1 family of plus-end-tracking proteins.   EB1 proteins in protists and metazoans regulate microtubule dynamics and cell polarity.   Arabidopsis has three EB1 genes and we are using reverse genetics to investigate their functions in plant cells.   These studies will be expanded to identify and investigate EB1 interacting proteins and other microtubule regulating proteins.

 

 

Figure One: Division planes (visualized by F-actin labeling, red) are positioned by spindle poles (visualized by microtubule labeling, green) in a polyspermic Silvetia zygote.

Figure Two: Roots of Arabidopsis seedlings carrying mutations in all three EB1 genes skew to the left.

References