  Background Despite its status as a model organism, the development of
Caenorhabditis elegans is not necessarily archetypical for nematodes. The
phylum Nematoda is divided into the Chromadorea (indcludes C. elegans) and the
Enoplea. Compared to C. elegans, enoplean nematodes have very different
patterns of cell division and determination. Embryogenesis of the enoplean
Romanomermis culicivorax has been studied in great detail, but the genetic
circuitry underpinning development in this species is unknown. Results We
created a draft genome of R. culicivorax and compared its developmental gene
content with that of two nematodes, C. elegans and Trichinella spiralis
(another enoplean), and a representative arthropod Tribolium castaneum. This
genome evidence shows that R. culicivorax retains components of the conserved
metazoan developmental toolkit lost in C. elegans. T. spiralis has
independently lost even more of the toolkit than has C. elegans. However, the
C. elegans toolkit is not simply depauperate, as many genes essential for
embryogenesis in C. elegans are unique to this lineage, or have only extremely
divergent homologues in R. culicivorax and T. spiralis. These data imply
fundamental differences in the genetic programmes for early cell specification,
inductive interactions, vulva formation and sex determination. Conclusions Thus
nematodes, despite their apparent phylum-wide morphological conservatism, have
evolved major differences in the molecular logic of their development. R.
culicivorax serves as a tractable, contrasting model to C. elegans for
understanding how divergent genomic and thus regulatory backgrounds can
generate a conserved phenotype. The availability of the draft genome will
promote use of R. culicivorax as a research model.
