The Murine Ortholog of Notchless, a Direct Regulator of the Notch Pathway in Drosophila melanogaster, Is Essential for Survival of Inner Cell Mass Cells

Abstract

Notch signaling is an evolutionarily conserved pathway involved in intercellular communication and is essential for proper cell fate choices. Numerous genes participate in the modulation of the Notch signaling pathway activity. Among them, Notchless (Nle) is a direct regulator of the Notch activity identified in Drosophila melanogaster. Here, we characterized the murine ortholog of Nle and demonstrated that it has conserved the ability to modulate Notch signaling. We also generated mice deficient for mouse Nle (mNle) and showed that its disruption resulted in embryonic lethality shortly after implantation. In late mNle^−/− blastocysts, inner cell mass (ICM) cells died through a caspase 3-dependent apoptotic process. Most deficient embryos exhibited a delay in the temporal down-regulation of Oct4 expression in the trophectoderm (TE). However, mNle-deficient TE was able to induce decidual swelling in vivo and properly differentiated in vitro. Hence, our results indicate that mNle is mainly required in ICM cells, being instrumental for their survival, and raise the possibility that the death of mNle-deficient embryos might result from abnormal Notch signaling during the first steps of development.

We thank J. Artus, S. Tajbakhsh, J. Hadchouel, F. Relaix, and C. Brou for helpful discussions, C. Kress for her invaluable help and instruction with culture and manipulation of ES cells, and S. Lecorre for technical help. We acknowledge the dynamic imaging platform, Institut Pasteur, for helpful assistance.

This work was supported by the Centre National de la Recherche Scientifique (CNRS), the Association pour la Recherche contre le Cancer (ARC), the Institut Pasteur GPH07 on stem cells, and the Action concertée incitative Biologie du Développement et Physiologie Intégrative from the Ministère de l'Education Nationale, de la Recherche, et de la Technologie. S.C. received grants from the Pasteur-Negri-Weizmann Council and the ARC. S.L.B. received funding from the Ministere de l'Education Nationale and was a recipient of funding from the ARC. C.S. received grants from CNRS (Bourse de Doctorat pour les Ingénieurs).