title: The developmental hourglass model: a predictor of the basic body plan?
abstract: The hourglass model of embryonic evolution predicts an hourglass-like divergence during animal embryogenesis - with embryos being more divergent at the earliest and latest stages but conserved during a mid-embryonic (phylotypic) period that serves as a source of the basic body plan for animals within a phylum. Morphological observations have suggested hourglass-like divergence in various vertebrate and invertebrate groups, and recent molecular data support this model. However, further investigation is required to determine whether the phylotypic period represents a basic body plan for each animal phylum, and whether this principle might apply at higher taxonomic levels. Here, we discuss the relationship between the basic body plan and the phylotypic stage, and address the possible mechanisms that underlie hourglass-like divergence.
authors.affiliation: Department of Biological Sciences, School of Science, University of Tokyo, Tokyo 113-0033, Japan irie@bs.s.u-tokyo.ac.jp saizo@cdb.riken.jp.
authors.forename: Naoki
authors.initials: N
authors.lastname: Irie
authors.affiliation: Group for Morphological Evolution, RIKEN Center for Developmental Biology, Kobe 650-0047, Japan irie@bs.s.u-tokyo.ac.jp saizo@cdb.riken.jp.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Kuratani
mesh_terms: D000818:Animals; D005075:Biological Evolution; D019521:Body Patterning / Q000502:physiology*; D047108:Embryonic Development / Q000502:physiology*; D020869:Gene Expression Profiling / Q000379:methods; D008954:Models, Biological; D038081:Organogenesis / Q000502:physiology*
keywords: Body plan; Evo-devo; Evolution; Hourglass model; Phylotype; Transcriptome