The role of thePax1/9gene in the early development of amphioxus pharyngeal gill slits

Abstract

The pharynx is a major characteristic of chordates. Compared with vertebrates, amphioxus has an advantage for the study of pharynx development, as embryos lack neural crest, and the pharynx is mainly derived from endoderm cells. The Pax1/9 subfamily genes have essential roles in vertebrate pharyngeal patterning, but it is not known if the Pax1/9 gene has similar functions in amphioxus pharynx development. To answer this question, we examined the Pax1/9 gene expression pattern in amphioxus embryos at different developmental stages, and observed morphological changes following Pax1/9 knockdown. RT-qPCR analysis indicated that Pax1/9 expression was initiated during early neurula stage and rapidly peaked during mid-neurula stage. Furthermore, in situ hybridization analysis showed that Pax1/9 transcripts were localized exclusively in the most endodermal region of the developing pharynx in early neurula stage embryos; however, Pax1/9 expression was strikingly down-regulated in the region where gill slits would form from the fusion of endoderm and ectoderm in subsequent developmental stages and was maintained in the border regions between adjacent gill slits. Knockdown of Pax1/9 function using both morpholino and siRNA approaches led to embryonic defects in the first three gill slits, and fusion of the first two gill slits. Moreover, the expression levels of the pharyngeal marker genes Six1/2 and Tbx1/10 were reduced in Pax1/9 knockdown embryos. From these observations, we concluded that the Pax1/9 gene has an important role in the initial differentiation of amphioxus pharyngeal endoderm and in the formation of gill slits, most likely via modulation of Six1/2 and Tbx1/10 expression.

Reiterative expression of pax1 directs pharyngeal pouch segmentation in medaka (Oryzias latipes)

“…Recent pax1/9 knockdown experiments in amphioxus revealed a role in gill slit segmentation and that pax1/9 deficiency leads to a reduction in tbx1/10 expression (Liu et al, 2015). The present study shows that the genetic regulation of pax1 and tbx1 and the function of pax1 in gill slit segmentation are conserved among aquatic chordates.…”

The sea cucumber genome provides insights into morphological evolution and visceral regeneration

“…1 was in another scaffold. The pax1/9 gene is important for formation of gill slits via modulation of six1/2 and tbx1/10 expression [107]. In A .…”

Joint profiling of gene expression and chromatin accessibility of amphioxus development at single cell resolution

“…The somite mesodermal lineage (G3.2) broke into 3 lineages, with the G5.7 lineage representing the anterior pharyngeal mesoderm (expressing Eya, Six4/5, and Pax3/7) 16,17 , the G5.3 lineage representing the posterior pharynx mesoderm (expressing Hox11) 18 and the G5.5 lineage likely representing the posterior tailbud mesoderm, which expresses the posterior marker Cdx (Figure 1E and Supplementary Figure 3) 19 . The endodermal lineage (G3.1) differentiated into the anterior pharynx lineage (expressing Six3/6 and Nkx2.1) 17,20 and posterior gut lineage (expressing Pax1/9, Ilp and Msxlx) [21][22][23] , which further differentiated into fore-, mid-, and hind-gut lineages at L0 stage (Figure 1E and Supplementary Figure 4). The neural ectodermal lineage differentiated into three populations at N3 stage, with the N3.4 and N3.7 representing the anterior (expressing higher Otx, Fezf, Pax4/6, Six3/6, Lhx2/9, OligA, OligB/C and Brn1/2/4) 17,[24][25][26][27] and posterior (expressing higher Gbx, Wnt7b, Pax2/5/8, Cdx, Hox1, Hox3 and Msx) cell populations 18,19,25,28-31 .…”