Fibroblast growth factor signalling controls nervous system patterning and pigment cell formation in Ciona intestinalis

Abstract

During the development of the central nervous system (CNS), combinations of transcription factors and signalling molecules orchestrate patterning, specification and differentiation of neural cell types. In vertebrates, three types of melanin-containing pigment cells, exert a variety of functional roles including visual perception. Here we analysed the mechanisms underlying pigment cell specification within the CNS of a simple chordate, the ascidian Ciona intestinalis. Ciona tadpole larvae exhibit a basic chordate body plan characterized by a small number of neural cells. We employed lineage-specific transcription profiling to characterize the expression of genes downstream of fibroblast growth factor signalling, which govern pigment cell formation. We demonstrate that FGF signalling sequentially imposes a pigment cell identity at the expense of anterior neural fates. We identify FGF-dependent and pigment cell-specific factors, including the small GTPase, Rab32/38 and demonstrated its requirement for the pigmentation of larval sensory organs.

Diverse ETS transcription factors mediate FGF signaling in the Ciona anterior neural plate

“…We also show that two different ETS family transcription factors mediate FGF signaling in row III. Whereas previous studies have shown that Ets1/2 is required in the lateral pigment cell precursors (PCPs; Squarzoni et al, 2011; Abitua et al, 2012; Racioppi et al, 2014), an additional ETS family transcription factor, Elk1/3/4, also appears to play a role in specifying row III cells. Dominant negative forms of Ets1/2 and Elk1/3/4 cause ectopic expression of Six3/6 (a row IV marker gene) in row III, loss of expression of the medial row III marker Myt1L , and loss of pigmented cells.…”

“…At this stage, FGF expression is restricted to row II, and the MAP kinase (MAPK) pathway component ERK1/2 is activated in the neighboring rows I and III (Hudson et al, 2007; Haupaix et al, 2014). Several recent studies show that FGF signaling is required for the specification of the pigmented cells of the otolith and ocellus, which arise from the lateral a9.49 cells of row III (Squarzoni et al, 2011; Haupaix et al, 2014; Racioppi et al, 2014). …”

A single cell transcriptional roadmap for cardiopharyngeal fate diversification

“…Single cell analyses comprehensively characterized very early embryonic stages (Tintori et al, 2016) , and the L2 larval stage in C. elegans (Cao, Junyue, Jonathan S. Packer, Vijay Ramani, Darren A. Cusanovich, Chau Huynh, Riza Daza, Xiaojie Qiu, et al, 2017) , but there are technical difficulties in isolated healthy single cells from embryos. By contrast, single cell suspensions can be obtained from dissociated Ciona embryos throughout development, lineage-specific cell populations can be isolated by FACS, and profiled using -omics methods (Christiaen et al, 2008(Christiaen et al, , 2009Racioppi et al, 2014;Razy-Krajka et al, 2014) . Moreover, Ciona emerged as an innovative chordate model to study conserved aspects of cardiopharyngeal development with unprecedented spatio-temporal resolution, and a well-established and invariant lineage (Kaplan et al, 2015;Wang et al, 2013) .…”

Purification of Fluorescent Labeled Cells from Dissociated Ciona Embryos

“…Although FACS is a sensitive and accurate method for purifying specific cells from the rest of embryonic cell population (Christiaen et al 2008; Christiaen et al 2009; Racioppi et al 2014; Razy-Krajka et al 2014), it requires specialized equipment and skilled operators, which are usually not available to individual laboratories, and since cells are processed through high-pressure fluids, they can easily be damaged. To circumvent these problems, affinity-based cell separation technologies are also adapted to isolating Ciona cells using membrane markers.…”