• Citer

Elucidating the Functional Role of Human Nucleoporin Nup88 in Health and Disease

par Bonnin, Edith
Président du jury Vanhamme, Luc
Promoteur Fahrenkrog, Birthe
Co-Promoteur Vanhollebeke, Benoît
Publication Non publié, 2018-02-27

Thèse de doctorat

• Accès en ligne
• Détails
• Contenu
• Statistiques

Résumé :

Movement is a prerequisite for normal fetal development and growth. Intrauterine movement restrictions cause a broad spectrum of disorders in which the unifying feature is a reduction or lack of fetal movement, giving rise to the term fetal akinesia deformations sequence (FADS [OMIM 208150]). FADS corresponds to a clinically and genetically heterogeneous constellation of properties and is characterized by multiple joint contractures, facial abnormalities, and lung hypoplasia as a result of the decreased in utero movement of the fetuses. Affected babies are often prematurely and stillborn, and those born alive typically die within minutes or hours after birth. The genetic causes for this fatal disorder are ill-defined as a genetic diagnosis is rarely executed, but mutations in three genes, namely RAPSN, DOK7, and MUSK, as well as in the subunits of the muscular nicotinic acetylcholine receptor (AChR) have been described. These mutations are thought to affect neuromuscular junctions, although this has not been proven experimentally.The nucleoporin NUP88 is a constituent of the nuclear pore complex (NPC), the gate for all trafficking between the nucleus and the cytoplasm. NUP88 resides on both the cytoplasmic and the nuclear side of NPCs, and it is found in two distinct subcomplexes. It associates with NUP214 and NUP62 on the cytoplasmic face, while on the nuclear side NUP88 binds NUP98 and the intermediate filament protein lamin A. The NUP88-NUP214-NUP62 complex plays an essential role in the nuclear export of a subset of proteins and pre-ribosomes, which is mediated by the nuclear export receptor CRM1. NUP88 in particular somewhat participates in the nuclear export of NF-κB proteins in a CRM1-dependent manner. Moreover, NUP88 is frequently overexpressed in a variety of human cancers, and its role in cancer appears linked to the deregulation of the anaphase-promoting complex. Here, we report the first Mendelian disorders caused by mutations in NUP88 and with that the first lethal developmental human disease due to mutations in a nuclear pore component. We demonstrate that biallelic mutations in NUP88 are likely to cause fetal akinesia of the Pena-Shokeir subtype. We confirm in zebrafish that loss of NUP88 impairs movement and the mutations identified in the affected individuals resemble a loss-of-function phenotype. We show that loss of NUP88 affects expression and localization of rapsyn, the protein encoded by RAPSN, in human and mouse cell lines, and patient samples. Consistent with altered rapsyn, AChR clustering and neuromuscular junction formation in zebrafish are abnormal. We therefore propose that defective NUP88 function cause FADS by affecting neuromuscular junction formation.Keywords: Nuclear pore complex, NUP88, Fetal Akinesia Deformation Sequence, rapsyn, acetylcholine receptor clustering, synaptic transmission, fetal development, inherited developmental disorder.