Divergent mechanisms regulate conserved cardiopharyngeal development and gene expression in distantly related ascidians
Alberto Stolfi,
Elijah K Lowe,
Claudia Racioppi,
Filomena Ristoratore,
C Titus Brown,
Billie J Swalla,
Lionel Christiaen
Affiliations
Alberto Stolfi
Center for Developmental Genetics, Department of Biology, New York University, New York, United States
Elijah K Lowe
Department of Computer Science and Engineering, Michigan State University, East Lansing, United States
Claudia Racioppi
Cellular and Developmental Biology Laboratory, Stazione Zoologica Anton Dohrn, Napoli, Italy
Filomena Ristoratore
Cellular and Developmental Biology Laboratory, Stazione Zoologica Anton Dohrn, Napoli, Italy
C Titus Brown
Department of Computer Science and Engineering, Michigan State University, East Lansing, United States; Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, United States
Billie J Swalla
Department of Biology, University of Washington, Seattle, United States; Friday Harbor Laboratories, University of Washington, Friday Harbor, United States
Lionel Christiaen
Center for Developmental Genetics, Department of Biology, New York University, New York, United States
Ascidians present a striking dichotomy between conserved phenotypes and divergent genomes: embryonic cell lineages and gene expression patterns are conserved between distantly related species. Much research has focused on Ciona or Halocynthia spp. but development in other ascidians remains poorly characterized. In this study, we surveyed the multipotent myogenic B7.5 lineage in Molgula spp. Comparisons to the homologous lineage in Ciona revealed identical cell division and fate specification events that result in segregation of larval, cardiac, and pharyngeal muscle progenitors. Moreover, the expression patterns of key regulators are conserved, but cross-species transgenic assays uncovered incompatibility, or ‘unintelligibility’, of orthologous cis-regulatory sequences between Molgula and Ciona. These sequences drive identical expression patterns that are not recapitulated in cross-species assays. We show that this unintelligibility is likely due to changes in both cis- and trans-acting elements, hinting at widespread and frequent turnover of regulatory mechanisms underlying otherwise conserved aspects of ascidian embryogenesis.
