Details

Autor(en) / Beteiligte

• Gasparini, Fabio
• Degasperi, Valentina
• Shimeld, Sebastian M.
• Burighel, Paolo
• Manni, Lucia

Titel

Evolutionary conservation of the placodal transcriptional network during sexual and asexual development in chordates

Ist Teil von

• Developmental dynamics, 2013-06, Vol.242 (6), p.752-766

Ort / Verlag

United States: Wiley Subscription Services, Inc

Erscheinungsjahr

2013

Link zum Volltext

Quelle

MEDLINE

Beschreibungen/Notizen

• Background: An important question behind vertebrate evolution is whether the cranial placodes originated de novo, or if their precursors were present in the ancestor of chordates. In this respect, tunicates are of particular interest as they are considered the closest relatives to vertebrates. They are also the only chordate group possessing species that reproduce both sexually and asexually, allowing both types of development to be studied to address whether embryonic pathways have been co‐opted during budding to build the same structures. Results: We studied the expression of members of the transcriptional network associated with vertebrate placodal formation (Six, Eya, and FoxI) in the colonial tunicate Botryllus schlosseri. During both sexual and asexual development, each transcript is expressed in branchial fissures and in two discrete regions proposed to be homologues to groups of vertebrate placodes. Discussion: Results reinforce the idea that placode origin predates the origin of vertebrates and that the molecular network involving these genes was co‐opted in the evolution of asexual reproduction. Considering that gill slit formation in deuterostomes is based on similar expression patterns, we discuss possible alternative evolutionary scenarios depicting gene co‐option as critical step in placode and pharynx evolution. Developmental Dynamics 242:752–766, 2013. © 2013 Wiley Periodicals, Inc. Key findings We here characterize B. schlosseri orthologues of Six1/2, Six3/6, Eya, and FoxI, and report their spatiotemporal expression patterns during both embryogenesis and blastogenesis in the colonial tunicate B. schlosseri. Our results show that these genes are expressed both in larva and bud during branchial fissure formation, and in two domains along the anterior–posterior axis. We hypothesize that the latter are placodal homologue territories that can be recognized during not only sexual but also asexual development of tunicates. We discuss the idea that placode origin predates the origin of vertebrates and the molecular network involving these genes was co‐opted in the evolution of asexual reproduction. We consider possible alternative evolutionary scenarios depicting gene co‐option as critical step in placode and pharynx evolution.