The epithelium of the pharynx contributes to the formation of gills in hemichordates, urochordates, cephalochordates and primitive vertebrates, and is therefore a key structure for understanding developmental mechanisms underlying the establishment of chordate body plans. Pax1- and Pax9-related genes encode transcription factors which are expressed in the pharyngeal region of cephalochordates as well as in the vertebrate pharyngeal pouch epithelium that forms the thymus and parathyroid glands. To explore the molecular basis underlying the occurrence and modifications of the pharyngeal epithelium during evolution, we isolated cDNA clones for Pax1- and Pax9-related genes of urochordates (HrPax1/9 of Halocynthia roretzi and CiPax1/9 of Ciona intestinalis) and a hemichordate (PfPax1/9 of Ptychodera flava) from gill cDNA libraries. Each gene is present as a single copy per haploid genome. All of the cDNAs encode typical paired domains and octapeptides but not a homeodomain, as is also true of other Pax1- and Pax9-related genes. Molecular phylogenetic analysis based on comparison of the paired domain amino-acid sequences suggests that HrPax1/9, CiPax1/9 and PfPax1/9 belong to the Pax1/9 subfamily, and that they are descendants of a single precursor of Pax1/Pax9. Screening of HrPax1/9 cDNA clones yielded six different types of transcripts which were generated by alternative splicing. Northern blot, RT-PCR/Southern and in situ hybridization analyses revealed that HrPax1/9, CiPax1/9 and PfPax1/9 are not expressed during early embryogenesis but are expressed in the epithelia of differentiating gills, suggesting that these genes encode gill-specific transcription factors. The Pax1/9 genes therefore might provide the first developmental genetic corroboration of hypotheses of organ-level homology that unifies hemichordates, urochordates and cephalochordates.
Developmental expression of Pax1/9 genes in urochordate and hemichordate gills: insight into function and evolution of the pharyngeal epithelium
M. Ogasawara, H. Wada, H. Peters, N. Satoh; Developmental expression of Pax1/9 genes in urochordate and hemichordate gills: insight into function and evolution of the pharyngeal epithelium. Development 1 June 1999; 126 (11): 2539–2550. doi: https://doi.org/10.1242/dev.126.11.2539
Download citation file:
Advertisement
Cited by
Pathway to Independence programme

We’re excited to announce our new Pathway to Independence programme, aimed at supporting postdocs as they go on the job market. Find out more about the scheme in our Editorial.
Call for papers: Metabolic and Nutritional Control of Development and Regeneration

We are welcoming submissions for our next special issue, which will focus on metabolic and nutritional control of development and regeneration. Submission deadline: 15 May 2023.
Webinar: Increasing the visibility and impact of your research
-HUBSwebinar.jpg?versionId=4486)
Would you like to increase the visibility and impact of your research and raise your profile internationally? If so, register for the very practical webinar we are running in association with HUBS on 23 February 2023.
Transitions in development: Daniel Grimes

Daniel Grimes’s lab studies the consequences of ciliary mutations, including left-right patterning defects and scoliosis. We interviewed Daniel to find out more about his career path, his experience of becoming a group leader and the influence of Jurassic Park.
Preprints in Development
(update)-InPreprints.png?versionId=4486)
As part of our efforts to support the use of preprints and help curate the preprint literature, we are delighted to launch a new article type: ‘In preprints’. These pieces will discuss one or more recent preprints and place them in a broader context.