Fig. 1. Expression of Oct4-related genes in somatic and embryonic tissues assayed by RT-PCR. Total cellular RNA samples were prepared from (left to right): adult brain, embryonic brain, embryonic limbs, adult skeletal muscles, lung, liver, spleen, kidney, heart, blastocysts (embryonic day E3.5), epiblasts (E7.0), purified primordial germ cells (E10), embryonic gonads (E12) and purified primitive type A spermatogonia (postnatal day 6). Gapd served as a ubiquitously expressed control. Oct4 is expressed in embryonic and germline tissues as described previously (Rosner et al., 1990; Yeom et al., 1996). Control reactions lacking reverse transcriptase or input cDNA showed no amplification products (data not shown). The ability of DNA-free reagent (Ambion) to eliminate residual genomic DNA in embryonic RNA samples was tested extensively in control experiments.