Asymmetric cell division and generation of polarity
Asymmetric cell divisions create diverse cell types and maintain stem-cell populations. In many systems, asymmetric division relies on asymmetric protein localization within the mother cell and between the daughters. For example, the PAR proteins are conserved animal polarity regulators that are localized to restricted regions of the cell periphery and influence cell fate by guiding division planes and by localizing cell fate regulators so that that these determinants are segregated to one daughter.
Plants, like animals, use asymmetric divisions for development and self-renewal; however, plant genomes do not encode homologues of the animal asymmetry regulators and structural features of plant cells preclude many of the animal cell division mechanisms. We have exploited the stereotyped asymmetric and oriented division pattern of Arabidopsis stomatal development to identify genes that serve as plant cells “asymmetry” regulators.
BASL is required for plant asymmetric divisions
BASL is required for the physical and cell fate asymmetry of stomatal lineage divisions. Moreover, BASL protein exhibits a unique and dynamic subcellular localization during asymmetric divisions; accumulating in the nucleus, in a crescent at the periphery, or in both locations, depending on the identity and division behavior of the stomatal lineage cell. In a reversal from the situation in animal stem-cell populations, BASL appears to be active at the cortex of the differentiating cell whereas nuclear localization serves a sequestration function. To our knowledge, BASL is the first protein reported to have this localization in plants and the only stem-cell associated protein that functions in this manner.
BASL is normally expressed only in stomatal lineage cells. However, when expressed in other cells, BASL accumulates in a peripheral crescent indicating that most, if not all, plant cells have machinery for polarized protein trafficking and maintenance at the periphery. BASL, therefore, provides an entry into the general problem of plant cell polarity.
We are currently asking: How is BASL trafficked and maintained at its polarized peripheral location? What is the function of BASL at the cell periphery? What is its function in the nucleus? What other proteins are required for asymmetric divisions in the stomatal lineage?
Relevant lab publications
Dong J, Macalister CA, Bergmann DC (2009) BASL Controls Asymmetric Cell Division in Arabidopsis. Cell. 2009 Jun 10. PMID: 19523675
Abrash EB, Bergmann DC (2009) Asymmetric cell divisions: a view from plant development. Dev Cell. 2009 Jun;16(6):783-96. PMID: 19531350
Funding by NSF, Terman, HFSP |
