Evolution of distinct expression patterns for engrailed paralogues in higher crustaceans (Malacostraca)

The segment-polarity gene engrailed of Drosophila melanogaster and its homo logues in other arthropods possess a highly conserved expression domain in the posterior portion of each segment. We report here that the two pan-spec ific antibodies, Mab4D9 and Mab4F11, reveal strikingly different accumulati on patterns in both of the malacostracan crustaceans Porcellio scaber (Isop oda) and Procambarus clarkii (Decapoda), compared with insects. The signal detected with Mab4D9 resides in the posterior part of each segment, includi ng the appendages, the ventral and lateral sides of the trunk and the CNS. However, Mab4F11 reveals a signal only in small groups of neurons in the CN S and PNS, primarily localized in the pereon. We observe similar Mab4D9 and Mab4F11 patterns in the crayfish P. clarkii, except that no Mab4F11 signal is detected in the pleon. To address the possibility of multiple engrailed paralogues, we cloned partial cDNAs of two engrailed genes, Ps-en1 and Ps- en2, from P. scaber, and studied their expression patterns using whole-moun t in situ hybridization. Although the Ps-en1 and Ps-en2 patterns are compar able in early development, they become distinct in late embryogenesis. Ps-e n1 is expressed in the CNS, where Mab4F11 stains, but also accumulates in t he epidermis. In contrast, Ps-en2 is expressed in the lateral aspect and li mbs of all segments. Phylogenetic analysis of en sequences from crustaceans and insects suggests that the two en genes from the apterygote insect Ther mobia domestica (Thysanura) may be related to en1 and en2 of higher crustac eans.