The Hedgehog pathway in penaeid shrimp: developmental expression and evolution of splice junctions in Pancrustacea

Penaeid shrimp embryos undergo holoblastic division, gastrulation by invagination, and hatching as a nauplius larva. Posterior segments form and differentiate during larval development. Hedgehog (Hh) pathway genes from penaeid shrimp and other pancrustaceans were identified by in silico analysis of genomes and transcriptomes, and mapped onto a recent pancrustacean phylogeny to determine patterns of intron gains and losses. Penaeus vannamei, P. japonicus, and P. monodon Hh proteins were encoded by four exons. Amphipod, isopod, and ostracod hh were also encoded by four exons, but hh from other arthropod groups contained three conserved exons. The novel hh intron is hypothesized to have arisen independently in the malacostracan ancestor and Ostracoda by a transposon insertion. Shared patterns of ptc, smo, and ci exon structure were found for Malacostraca, Branchiopoda + Hexapoda, Hexanauplia (Thecostraca + Copepoda), Multicrustacea (Thecostraca + Copepoda + Malacostraca), and Pancrustacea minus Oligostraca. mRNA expression of P. vannamei of hh, ptc, and ci from developmental transcriptomes of zygotes through postlarvae showed low expression from zygote to gastrula, which increased at limb bud, peaked at unhatched nauplius, and declined in nauplius and later larval stages. smo expression was found in zygotes, peaked in gastrula, and declined in limb bud and later stages. These results are consistent with a role for Hh signaling during segmentation in penaeid shrimp.