Conserved functional antagonism of CELF and MBNL proteins controls stem cell-specific alternative splicing in planarians.

Jordi Solana,Manuel Irimia,Quaid Morris,Benjamin J Blencowe,Salah Ayoub,Marvin Jens,Debashish Ray,Javier Tapial,Marta Rodriguez Orejuela,Timothy R Hughes,Vera Zywitza,Nikolaus Rajewsky

doi:10.7554/elife.16797

Abstract

In contrast to transcriptional regulation, the function of alternative splicing (AS) in stem cells is poorly understood. In mammals, MBNL proteins negatively regulate an exon program specific of embryonic stem cells; however, little is known about the in vivo significance of this regulation. We studied AS in a powerful in vivo model for stem cell biology, the planarian Schmidtea mediterranea. We discover a conserved AS program comprising hundreds of alternative exons, microexons and introns that is differentially regulated in planarian stem cells, and comprehensively identify its regulators. We show that functional antagonism between CELF and MBNL factors directly controls stem cell-specific AS in planarians, placing the origin of this regulatory mechanism at the base of Bilaterians. Knockdown of CELF or MBNL factors lead to abnormal regenerative capacities by affecting self-renewal and differentiation sets of genes, respectively. These results highlight the importance of AS interactions in stem cell regulation across metazoans.

Highlights

Stem cells are found in all animals and are defined by their capacity to self-renew and to differentiate into different cell types (Sanchez Alvarado and Yamanaka, 2014)
Our results show that alternative splicing (AS) and the factors involved in its regulation, as well as their specific interactions, are crucial for planarian stem cell biology and regeneration and likely a deeply conserved feature of animal stem cells
Taken together our results show that both CELF and MBNL factors are required for regeneration in planarians in vivo, and that they act by antagonizing each other in the control of neoblast self-renewal and differentiation

Summary

Introduction

Stem cells are found in all animals and are defined by their capacity to self-renew and to differentiate into different cell types (Sanchez Alvarado and Yamanaka, 2014). One of the most extreme examples are freshwater planarians, from which almost any body part can regenerate a complete organism in a few days. This ability relies on a large number of stem cells present in the adult, called neoblasts. Illustrating their pluripotency, single neoblasts transplanted into lethally irradiated hosts can rescue this lethality, restore tissue turnover, generate all cell types of the adult planarian and completely transform the genotype and phenotype of the host into that of the donor (Wagner et al, 2011).

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Conclusion