We have generated a Xenopus laevis expressed sequence tag (EST) collection from unfertilized eggs. These large cells contain all the maternal mRNA necessary for the first several hours and first cell divisions in developing Xenopus, since new DNA synthesis does not begin in this organism until after the mid-blastula transition. The use of eggs in this collection avoids the contamination of isolated oocytes with follicular cells. We have sequenced more than 15,000 ESTs from a normalized library from eggs; this has recently been subtracted and a new round of sequencing the subtracted library has begun. This EST collection comprises almost 50% of the total Xenopus ESTs in the database at present. We have used PCR products from a subset of these ESTs to build prototype microarrays, which will ultimately be used in studies of early Xenopus development, including toxicology, drug testing, oligonucleotide or antibody perturbation of development, adding genetic information to the FETAX test system already available, etc. Early testing of these microarrays is currently underway.
