The Interactive Fly
Evolutionarily conserved developmental pathways
Vertebrate segmentation has been explained as an evolutionary inheritance from either some metameric protostome or from a more closely related deuterostome. AmphiEn is the engrailed homolog inamphioxus (Cephalochordata), an animal that is the closest living invertebrate relative to the vertebrate line. In neurula embryos ofamphioxus, AmphiEn is expressed along the anteroposterior axis in metameric stripes, eachlocated in the posterior part of a nascent or newly formed segment. This pattern resemblesthe expression stripes of Drosophila engrailed, which has a key role inestablishing and maintaining the segments of Drosophila. Later in development, amphioxus embryos express AmphiEn in non-metameric patterns. Compared to vertebrate engrailedexpression at the midbrain/hindbrain boundary, AmphiEn expression in the cerebral vesicleis relatively late. The segmental expression of AmphiEn in formingsomites suggests that the functions of engrailed homologs in establishing and maintaining ametameric body plan may have arisen only once during animal evolution. If so, theprotostomes and deuterostomes probably shared a common segmented ancestor (Holland, 1997).
Holland, L. Z., et al. (1997). Sequence and embryonic expression of theamphioxus engrailed gene (AmphiEn): the metameric pattern of transcription resemblesthat of its segment-polarity homolog in Drosophila. Development 124: 1723-1732. PubMed Citation: 9165120
date revised: 30 June 97
Developmental Pathways conserved in Evolution
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