Cells in developing organisms have to robustly assume a correct fate in order to fulfill their specific function. However, some cell fate decisions are made in a stochastic manner, with cells randomly choosing one cell fate out of a repertoire of different possible ones. It is thought that stochastic cell fate decisions exploit molecular fluctuations, so-called molecular noise, by using positive feedback loops in the signaling network to amplify this noise into discrete cell fates. However, how a cell uses such a stochastic process to reliably drive cell fate decisions is an open question. We address this question by a novel quantitative approach, studying one of the genetically best-understood stochastic cell fate decisions: the AC/VU decision in C. elegans gonad development. During the AC/VU decision two initially equivalent cells, Z1.ppp and Z4.aaa, interact, so that one cell becomes the anchor cell (AC) and the other cell a ventral uterine precursor cell (VU). Both cells are born at similar times and it is thought that after birth small stochastic fluctuations are amplified by lateral Notch signaling, leading to one cell expressing only the Notch receptor
lin-12 (VU) and the other cell only its ligand
lag-2 (AC). However, both the nature of the initial noise sources and the efficiency with which these are amplified are not well understood. Here, we use single molecule FISH and a newly developed setup combining microchambers with timelapse-fluorescent microscopy, to obtain quantitative data on the stochastic expression dynamics of
lag-2 and
lin-12, both in fixed and live animals. Preliminary results using smFISH indicate that
lag-2 is expressed at highest levels already in Z1.pp and Z4.aa, the mother cells of Z1.ppp and Z4.aaa, whereas
lin-12 is expressed at high levels only in Z1.ppp and Z4.aaa. In addition, we were able to quantify for the first time the expression dynamics of
lag-2 in individual live animals over many hours during the AC/VU decision process using timelapse microscopy. We find significant variability of
lag-2 expression dynamics between individual animals. Both the smFISH and the time-lapse microscopy results suggest that the AC/VU decision process can take as long as eight hours.