The neurofibromin GAP-related domain rescues endothelial but not neural crest development in Nf1–/– mice
Fraz A. Ismat, … , Min Min Lu, Jonathan A. Epstein
Fraz A. Ismat, … , Min Min Lu, Jonathan A. Epstein
Published September 1, 2006
Citation Information: J Clin Invest. 2006;116(9):2378-2384. https://doi.org/10.1172/JCI28341.
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Research Article Cardiology

The neurofibromin GAP-related domain rescues endothelial but not neural crest development in Nf1–/– mice

Abstract

Neurofibromatosis type I (NF1; also known as von Recklinghausen’s disease) is a common autosomal-dominant condition primarily affecting neural crest–derived tissues. The disease gene, NF1, encodes neurofibromin, a protein of over 2,800 amino acids that contains a 216–amino acid domain with Ras–GTPase-activating protein (Ras-GAP) activity. Potential therapies for NF1 currently in development and being tested in clinical trials are designed to modify NF1 Ras-GAP activity or target downstream effectors of Ras signaling. Mice lacking the murine homolog (Nf1) have mid-gestation lethal cardiovascular defects due to a requirement for neurofibromin in embryonic endothelium. We sought to determine whether the GAP activity of neurofibromin is sufficient to rescue complete loss of function or whether other as yet unidentified functions of neurofibromin might also exist. Using cre-inducible ubiquitous and tissue-specific expression, we demonstrate that the isolated GAP-related domain (GRD) rescued cardiovascular development in Nf1–/– embryos, but overgrowth of neural crest–derived tissues persisted, leading to perinatal lethality. These results suggest that neurofibromin may possess activities outside of the GRD that modulate neural crest homeostasis and that therapeutic approaches solely aimed at targeting Ras activity may not be sufficient to treat tumors of neural crest origin in NF1.

Authors

Fraz A. Ismat, Junwang Xu, Min Min Lu, Jonathan A. Epstein

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Figure 5

Tie2-cre –mediated expression of HA-GRD rescues cardiac development and hematologic abnormalities.

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Tie2-cre –mediated expression of HA-GRD rescues cardiac development and...
(A and B) Cardiac rescue with endothelial expression of HA-GRD. Representative low-power photomicrographs (magnification, ×4) of E17.5 wild-type (A) and Nf1–/–, HA-GRDk/+, Tie2-cre+ (B) littermates. There was normal cardiac anatomy, and the inflow valves (arrows) were comparable. However, there was marked enlargement of the dorsal root ganglia (arrowheads) in B compared with wild type. Higher-power images (magnification, ×10) of the dorsal root ganglia for wild-type (C) and Nf1–/–, HA-GRDk/+, Tie2-cre+ (D) littermates. (E–J) HA-GRD expression rescues hematologic abnormalities of the Tie2-cre–mediated loss of Nf1. Gross (E–G) and low-power hematoxylin and eosin photomicrographs (H–J; magnification, ×4) of spleens from affected mice and controls. A few Nf1flox/–, Tie2-cre+ mice survived embryonic development, but went on to develop a myeloproliferative disorder ultimately resembling juvenile myelomonocytic leukemia. This disease was manifest by gross splenic enlargement (F) and loss of normal architecture (I) compared with Nf1flox/– (E and H). In a Nf1flox/–, HA-GRDk/+, Tie2-cre+ littermate (G and J), in which HA-GRD was expressed under the same cre, there was less severe splenic enlargement (G) and a partial rescue of splenic tissue architecture (J).