Modern diagnostics and treatments for inherited and acquired cardiovascular diseases require in-depth knowledge of the mechanisms that control heart cell identity during embryonic development. In mammals, the facial and lower jaw muscles - collectively referred to as pharyngeal muscles - share a common origin with heart progenitors in the cardiopharyngeal mesoderm. This relationship is reflected in the DiGeorge syndrome, where altered Tbx1 function causes cardiovascular and craniofacial malformations. The heart vs. pharyngeal muscle fate choice is difficult to study in the early mammalian embryos, as is the cellular environment, a.k.a. niche, which determines whether cardiopharyngeal progenitor cells remain multipotent or become specified into either cardiac or pharyngeal muscles. Larvae of the ascidian Ciona intestinalis, a marine invertebrate among the closest relatives to the vertebrates, possess a simplified cardiopharyngeal lineage of cells that make successive heart vs. pharyngeal muscles choices in a simple and stereotyped manner. This can be studied with high spatiotemporal resolution using targeted molecular perturbations, confocal microscopy and lineage- specific transcription profiling that combines fluorescence activated cell sorting (FACS) and next generation RNA sequencing (RNA-seq). The ascidian cardiopharyngeal mesoderm arises from two progenitors, which produce the heart and the atrial siphon muscles (ASM) that control the exhalant opening. It was found that bipotent cardiopharyngeal progenitors undergo oriented asymmetrical cell divisions that produce distinct first and second heart precursors and ASM precursors. Molecularly, the cardiopharyngeal progenitors display multilineage transcriptional priming, i.e. they activate both early cardiac and ASM programs. These then segregate to their corresponding precursors due to regulatory cross-antagonisms: early ASM regulators inhibit the heart program in ASM precursors, while the ASM program is inhibited in the heart precursors. Here, regulatory mechanisms governing progressive ASM fate specification will be analyzed by testing the hypothesis that feedforward regulatory circuits control sequential gene activation. Next, the hypothesis that the orientation of asymmetric cell division determines differential interaction between a specific niche and the ASM vs. heart precursors will be explored. Finally, defined tissue-specific molecular perturbations, FACS and RNA-seq assays, including from single-cell samples, will define transcriptional signatures for multipotent cardiopharyngeal progenitors, first and second heart precursors and early ASM precursors. These results will characterize the regulatory properties that define cardiopharyngeal multipotency and uncover mechanisms that regulate conserved heart vs. pharyngeal muscle fate choices in chordates.
Treatments and diagnostics of cardiovascular diseases require in-depth knowledge of the mechanisms that govern heart development in the embryo. The heart and a subset of head muscles arise from multipotent progenitors, which remain poorly characterized, as do the mechanisms that control the cardiac vs. facial muscle fate choice in the early embryo. Here, we propose to harness the unique property of an innovative chordate model system to characterize the multipotent stem cell-like progenitors and study the earliest cellular and molecular events underlying a conserved heart vs. pharyngeal muscle fate choice with unprecedented spatiotemporal resolution.
|Lam, Kari Y; Westrick, Zachary M; Müller, Christian L et al. (2016) Fused Regression for Multi-source Gene Regulatory Network Inference. PLoS Comput Biol 12:e1005157|
|Brozovic, Matija; Martin, Cyril; Dantec, Christelle et al. (2016) ANISEED 2015: a digital framework for the comparative developmental biology of ascidians. Nucleic Acids Res 44:D808-18|
|Anderson, Heather Evans; Christiaen, Lionel (2016) Ciona as a Simple Chordate Model for Heart Development and Regeneration. J Cardiovasc Dev Dis 3:|
|Tolkin, Theadora; Christiaen, Lionel (2016) Rewiring of an ancestral Tbx1/10-Ebf-Mrf network for pharyngeal muscle specification in distinct embryonic lineages. Development 143:3852-3862|
|Kaplan, Nicole; Razy-Krajka, Florian; Christiaen, Lionel (2015) Regulation and evolution of cardiopharyngeal cell identity and behavior: insights from simple chordates. Curr Opin Genet Dev 32:119-28|
|Stolfi, Alberto; Sasakura, Yasunori; Chalopin, Domitille et al. (2015) Guidelines for the nomenclature of genetic elements in tunicate genomes. Genesis 53:1-14|
|Diogo, Rui; Kelly, Robert G; Christiaen, Lionel et al. (2015) A new heart for a new head in vertebrate cardiopharyngeal evolution. Nature 520:466-73|
|Razy-Krajka, Florian; Lam, Karen; Wang, Wei et al. (2014) Collier/OLF/EBF-dependent transcriptional dynamics control pharyngeal muscle specification from primed cardiopharyngeal progenitors. Dev Cell 29:263-76|
|Stolfi, Alberto; Gandhi, Shashank; Salek, Farhana et al. (2014) Tissue-specific genome editing in Ciona embryos by CRISPR/Cas9. Development 141:4115-20|
|Haupaix, Nicolas; Stolfi, Alberto; Sirour, Cathy et al. (2013) p120RasGAP mediates ephrin/Eph-dependent attenuation of FGF/ERK signals during cell fate specification in ascidian embryos. Development 140:4347-52|
Showing the most recent 10 out of 15 publications