title: The spatial and temporal expression of Ch-en, the engrailed gene in the polychaete Chaetopterus, does not support a role in body axis segmentation.
abstract: We are interested in understanding whether the annelids and arthropods shared a common segmented ancestor and have approached this question by characterizing the expression pattern of the segment polarity gene engrailed (en) in a basal annelid, the polychaete Chaetopterus. We have isolated an en gene, Ch-en, from a Chaetopterus cDNA library. Genomic Southern blotting suggests that this is the only en class gene in this animal. The predicted protein sequence of the 1.2-kb cDNA clone contains all five domains characteristic of en proteins in other taxa, including the en class homeobox. Whole-mount in situ hybridization reveals that Ch-en is expressed throughout larval life in a complex spatial and temporal pattern. The Ch-en transcript is initially detected in a small number of neurons associated with the apical organ and in the posterior portion of the prototrochophore. At later stages, Ch-en is expressed in distinct patterns in the three segmented body regions (A, B, and C) of Chaetopterus. In all segments, Ch-en is expressed in a small set of segmentally iterated cells in the CNS. In the A region, Ch-en is also expressed in a small group of mesodermal cells at the base of the chaetal sacs. In the B region, Ch-en is initially expressed broadly in the mesoderm that then resolves into one band/segment coincident with morphological segmentation. The mesodermal expression in the B region is located in the anterior region of each segment, as defined by the position of ganglia in the ventral nerve cord, and is involved in the morphogenesis of segment-specific feeding structures late in larval life. We observe banded mesodermal and ectodermal staining in an anterior-posterior sequence in the C region. We do not observe a segment polarity pattern of expression of Ch-en in the ectoderm, as is observed in arthropods.
authors.affiliation: Kewalo Marine Lab, PBRC/University of Hawaii, 41 Ahui Street, Honolulu, Hawaii 96813, USA. seaver@hawaii.edu
authors.forename: E C
authors.initials: EC
authors.lastname: Seaver
authors.forename: D A
authors.initials: DA
authors.lastname: Paulson
authors.forename: S Q
authors.initials: SQ
authors.lastname: Irvine
authors.forename: M Q
authors.initials: MQ
authors.lastname: Martindale
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000845:Annelida; D001483:Base Sequence; D015139:Blotting, Southern; D019521:Body Patterning; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D015723:Gene Library; D018398:Homeodomain Proteins / Q000096:biosynthesis* / Q000235:genetics*; D017403:In Situ Hybridization; D007814:Larva / Q000502:physiology; D008648:Mesoderm / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014018:Tissue Distribution; D014157:Transcription Factors
chemical_list: C433924:Ch-en protein, Chaetopterus; D018076:DNA, Complementary; D018398:Homeodomain Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; C106185:engrailed homeobox proteins