Engrailed in the cockroach Periplaneta americana : cloning, expression and role in specifying synaptic connections.
engrailed-related genes are homeobox containing transcription factors and have been
cloned in numerous taxa. Their roles, in segmentation of the early embryo and in neural
development, have been extensively described. Within the insects, some species have a
single engrailed-related gene whilst others have two copies, raising the question of when
and how often this duplication occurred.
Here I report the cloning of two engrailed-related genes cren 1 and cren 2 in the
cockroach Periplaneta americana. By comparing conserved domains and by carrying out a
phylogenetic analysis, I conclude that these two genes are likely to be the product of a
recent duplication in the cockroach lineage. Differentially spliced cren 2 isoforms that lack
some regulatory domains have also been isolated. The roles these isoforms could play in
regulating developmental processes are discussed. cren 1 and cren 2 are co-expressed
during early embryogenesis; their segmental pattern of expression appears in an anteriorposterior
Double-stranded RNA interference was used to abolish the expression of Engrailed
which is a putative positional determinant in an array of sensory neurones in the cockroach
cereal system. This treatment radically alters the axonal arborization and choice of
postsynaptic interneural partners of an identified Engrailed-positive sensory afferent. The
neurone now resembles a neighbouring, Engrailed-negative cell, which is itself unaffected
by the double-stranded RNA.