Abstract: A method for the identification of a nucleic acid molecule differentially expressed in an in vitro model of a biological system, comprising the steps of: (1) harvesting cells from the model system at predetermined time points; (2) obtaining total RNA from the cells harvested at each time point; (3) preparing cDNA from the total RNA from each time point to provide a plurality of pools of cDNA; (4) performing a suppression subtractive hybridization (SSH) on the cDNA pools from each time point sequentially so as to progressively amplify cDNAs derived from nucleic acid molecules differentially expressed from one time period to the next.