To test early-gestation human placenta, a human trophoblast cell line, mouse eggs, preimplantation embryos, and a mouse trophoblast cell line for the expression of mRNA transcripts for stress-activated protein kinase/c-Jun N-terminal kinase (SAPKgamma/JNK1, SAPKalpha/JNK2, and SAPKbeta/JNK3).Whole RNA was isolated from the tissue sources listed above and control tissues, and reverse transcription-polymerase chain reaction (RT-PCR) was performed to assay for the qualitative and semiquantitative presence of SAPKgamma/JNK1, SAPKalpha/JNK2, and SAPKbeta/JNK3.None.None.None.The presence and magnitude of amplimer amounts in gels or gene hybridization on Affymetrix cDNA arrays of RT-PCR products of reactions for SAPKgamma/JNK1, SAPKalpha/JNK2, and SAPKbeta/JNK3.SAPKgamma/JNK1 and SAPKalpha/JNK2 mRNA transcripts are present in early-gestation human placenta, a human trophoblast cell line, mouse eggs, preimplantation embryos, and a mouse trophoblast cell line at levels similar to positive control levels. SAPKalpha/JNK2 is expressed at the highest level of the three transcripts in the family. SAPKbeta/JNK3 is present at levels that are 1/100-1/1,000 those of the positive control and in some cases at the apparent level of the negative control (previously measured by the less-sensitive Northern blot analysis). Analysis with an Affymetrix cDNA array suggested that SAPKalpha/JNK2 and 38 kDa mitogen-activated protein kinase had the highest mRNA expression measured for each of three family members.Mitotic placental trophoblast cell lines and primary conceptus/embryo samples containing early placental trophoblasts express SAPKalpha/JNK2 at higher levels than SAPKgamma/JNK1, but not (only low background levels of) SAPKbeta/JNK3 mRNA transcripts. This suggests that SAPKgamma/JNK1 and SAPKalpha/JNK2 may be important mediators of stress-induced responses in early implanting conceptuses that could mediate embryo loss.