Pax37 gene function inOikopleura dioicasupports a neuroepithelial-like origin for its house-making Fol territory

Abstract

AbstractLarvacean tunicates feature a spectacular innovation not seen in other animals - the trunk oikoplastic epithelium (OE). This epithelium produces a house, a large and complex extracellular structure used for filtering and concentrating food particles. Previously we have shown that several homeobox transcription factors may play a role in patterning the OE. Among these are twoPax3/7duplicates that we namedPax37AandPax37B. The vertebrate homologs,PAX3andPAX7, are involved in developmental processes related to neural crest and muscles. In the ascidian tunicateCiona robusta,Pax3/7has been given a role in development of cells deriving from the neural plate border including trunk epidermal sensory neurons and tail nerve cord neurons as well as in neural tube closure. Here we have investigated the roles ofPax37AandPax37Bin the development of the OE using CRISPR-Cas9, analyzing scRNA-seq data from wild-type animals that were compared with scRNA-seq data fromC. robusta. We revealed thatPax37Bbut notPax37Ais essential for the differentiation of cell fields that produce the food concentrating filter of the house: the anterior Fol, giant Fol and Nasse cells. Lineage analysis supports that expression ofPax37is under influence of Wnt signaling and that Fol cells have a neuroepithelial-like transcriptional signature. We propose that the highly specialized secretory epithelial cells of the Fol region either maintained or evolved neuroepithelial features as do “glue” secreting collocytes of ascidians. Their development seems to be controlled by a GRN that also operates in some ascidian neurons.