Polar body emission.

Generation of a haploid female germ cell, the egg, consists of two rounds of asymmetric cell division (meiosis I and meiosis II), yielding two diminutive and nonviable polar bodies and a large haploid egg. Animal eggs are also unique in the lack of centrioles and therefore form meiotic spindles without the pre-existence of the two dominant microtubule organizing centers (centrosomes) found in mitosis. Meiotic spindle assembly is further complicated by the unique requirement of sister chromatid mono-oriented in meiosis I. Nonetheless, the eggs appear to adopt many of the same proteins and mechanisms described in mitosis, with necessary modifications to accommodate their special needs. Unraveling these special modifications will not only help understanding animal reproduction, but should also enhance our understanding of cell division in general.

FRAP-based analysis of Rho GTPase-dependent polar exocytosis in pollen tubes.

The regulation of exocytosis by Rho GTPases is conserved in eukaryotic kingdoms. Given the spatiotemporal dynamics of Rho GTPase activity, a method for visualizing exocytosis with high space and time resolution will be an important tool for the functional analysis of Rho GTPases. During tip growth of pollen tubes, both cell wall material and plasma membrane are renewed via rapid exocytosis. ROP1 GTPase, a plant Rho GTPase, is localized to the apical plasma membrane of pollen tubes and controls polar exocytosis via regulation of F-actin dynamics. Here, we describe a fluorescence recovery after photobleaching (FRAP) method for the analysis of exocytosis dynamics in living pollen tubes. This method has been shown to be a valuable tool for studying the effect of ROP1-dependent F-actin dynamics on polar exocytosis in pollen tubes and may also be applicable to other systems.