Pk. Dearden et M. Akam, Early embryo patterning in the grasshopper, Schistocerca gregaria: wingless, decapentaplegic and caudal expression, DEVELOPMENT, 128(18), 2001, pp. 3435-3444
Although the molecular pathways that pattern the early embryo of Drosophila
melanogaster are well understood, how these pathways differ in other types
of insect embryo remains largely unknown. We have examined the expression
of three markers of early patterning in the embryo of the African plague lo
cust Schistocerca gregaria, an orthopteran insect that displays a mode of e
mbryogenesis very different from that of Drosophila. Transcripts of the cau
dal gene are expressed maternally and are present in all cells that aggrega
te to form the early embryonic rudiment. First signs of a posterior-to-ante
rior gradient in the levels of caudal transcript appear in the early heart-
stage embryo, shortly before gastrulation. This gradient rapidly resolves t
o a defined expression domain marking segment A11. The decapentaplegic (dpp
) gene, which encodes a transforming growth factor beta family ligand, is f
irst expressed in a circle of cells that delimit the margins of the embryon
ic primordium, where embryonic and extra-embryonic tissues abut. Patterned
transcription of wingless reveals that the first segments are delineated in
the Schistocerca embryo substantially earlier than previously thought, at
least 14-16 hours before the onset of engrailed expression. By the late hea
rt-stage, gnathal and thoracic segments are all defined. Thus, with respect
to the molecular patterning of segments, the short germ Schistocerca embry
o differs little from intermediate germ embryos. The expression of these ma
rker genes suggests that embryonic pattern formation in the grasshopper occ
urs as cells move together to form the blastodisc.