The two Drosophila p38 genes exhibit different embryonic expression patterns.
Zygotic expression is below the detectable level during most of embryonic development.
However, Northern analysis demonstrates the presence of low mRNA levels throughout development. At stage 16, there is a low level of staining in the posterior region, which may correspond to the developing hindgut. The preblastoderm staining indicates that Mpk2 may participate in early embryonic development. The p38b gene is expressed throughout embryonic development. There is a high level of maternal deposition, and at later stages, zygotic expression is present in most of the tissues.