Evolutionary crossroads in developmental biology: hemichordates

Abstract

Hemichordates are a deuterostome phylum, the sister group to echinoderms, and closely related to chordates. They have thus been used to gain insights into the origins of deuterostome and chordate body plans. Developmental studies of this group have a long and distinguished history. Recent improvements in animal husbandry, functional tool development and genomic resources have resulted in novel developmental data from several species in this group. In this Primer, we introduce representative hemichordate species with contrasting modes of development and summarize recent findings that are beginning to yield important insights into deuterostome developmental mechanisms.

Hemichordata

“…Strangely, the interest in enteropneust research declined within the last half of the twentieth century and relatively few works were published. Only recently, with upcoming immunocytochemical as well as molecular techniques and the new fi eld of "EvoDevo" research, people have rediscovered the potential and importance of enteropneusts in unravelling evolutionary developmental questions (Tagawa et al 1998a , b ;Lowe et al 2003Lowe et al , 2006Röttinger and Martindale 2011 ;Röttinger and Lowe 2012 ; and references therein).…”

“…With the exception of the strictly endodermal expression of foxA in Saccoglossus kowalevskii (Darras et al 2011 ;Fritzenwanker et al 2014 ), bra and chordin transcripts are also detected in ventral domains in S. kowalevskii and Ptychodera fl ava ( Fig. 2.11 ; Tagawa et al 1998b ;Röttinger and Lowe 2012 ), suggesting that a Nodal-dependent mechanism may be required to defi ne ventral domains in hemichordates.…”

FGF signaling repertoire of the indirect developing hemichordate Ptychodera flava

“…In this study, we investigated the FGF signaling repertoire in another hemichordate acorn worm species (Ptychodera flava) that exhibits indirect development with a long pelagic larval stage before metamorphosis into an adult body plan (Rottinger and Lowe, 2012). We found at least five FGFs and three FGFRs from the P. flava transcriptome database (Chen et al, 2014).…”

FGF signaling induces mesoderm in the hemichordate Saccoglossus kowalevskii

“…To investigate a potentially conserved role of FGF signaling in deuterostome mesoderm induction, we examined the role of FGF signaling during early development of the direct-developing hemichordate Saccoglossus kowalevskii (Bateson, 1884;Bateson, 1886;Colwin and Colwin, 1953;Lowe et al, 2004;Gerhart et al, 2005;Röttinger and Lowe, 2012). We tested the function of the FGF ligand FGF8/17/18 and the FGF receptor FGFR-B (Rebscher et al, 2009) in hemichordate mesoderm formation, and our work demonstrates that FGF8/17/18 signals from ectoderm to the underlying archenteron to induce mesoderm.…”