MIM-Induced Membrane Bending Promotes Dendritic Spine Initiation

• DOI: 10.1016/j.devcel.2015.04.014
• Publication Date: 2015-06-06T05:50:39Z
• Authors: Juha Saarikangas; Nazim Kourdougli; Yosuke Senju; Genevieve Chazal; Mikael Segerstråle; Rimante Minkeviciene; Jaakko Kuurne; Pieta K. Mattila; Lillian Garrett; Sabine M. Hölter; Lore Becker; Ildikó Racz; Wolfgang Hans; Thomas Klopstock; Wolfgang Wurst; Andreas Zimmer; Helmut Fuchs; Valérie Gailus-Du...; Martin Hrabě de A...; Lotta von Ossowski; Tomi Taira; Pekka Lappalainen; Claudio Rivera; Pirta Hotulainen
• Keywords: Male; Phosphatidylinositol 4,5-Diphosphate; metabolism [Actin-Related Protein 2-3 Complex]; metabolism [Hippocampus]; Hippocampus; Mice; Cerebellum; deficiency [Microfilament Proteins]; Tissue Distribution; metabolism [Phosphatidylinositol 4,5-Diphosphate]; Mice, Knockout; 0303 health sciences; Behavior, Animal; Microfilament Proteins; Mtss1 protein, mouse; metabolism [Cerebellum]; physiology [Neurogenesis]; physiology [Dendritic Spines]; growth & development [Nerve Net]; Neoplasm Proteins; physiology [Behavior, Animal]; genetics [Neurogenesis]; physiology [Neoplasm Proteins]; physiology [Nerve Net]; Female; ultrastructure [Dendritic Spines]; genetics [Synaptic Transmission]; metabolism [Actins]; Dendritic Spines; Neurogenesis; Models, Neurological; physiology [Microfilament Proteins]; metabolism [RNA, Messenger]; Actin-Related Protein 2-3 Complex; deficiency [Neoplasm Proteins]; genetics [RNA, Messenger]; 03 medical and health sciences; ultrastructure [Nerve Net]; Animals; ddc:610; RNA, Messenger; genetics [Neoplasm Proteins]; Actins; Mice, Inbred C57BL; physiology [Synaptic Transmission]; ultrastructure [Synapses]; Synapses; genetics [Microfilament Proteins]; physiology [Synapses]; Nerve Net; Developmental Biology

Proper morphogenesis of neuronal dendritic spines is essential for the formation of functional synaptic networks. However, it is not known how spines are initiated. Here, we identify the inverse-BAR (I-BAR) protein MIM/MTSS1 as a nucleator of dendritic spines. MIM accumulated to future spine initiation sites in a PIP2-dependent manner and deformed the plasma membrane outward into a proto-protrusion via its I-BAR domain. Unexpectedly, the initial protrusion formation did not involve actin polymerization. However, PIP2-dependent activation of Arp2/3-mediated actin assembly was required for protrusion elongation. Overexpression of MIM increased the density of dendritic protrusions and suppressed spine maturation. In contrast, MIM deficiency led to decreased density of dendritic protrusions and larger spine heads. Moreover, MIM-deficient mice displayed altered glutamatergic synaptic transmission and compatible behavioral defects. Collectively, our data identify an important morphogenetic pathway, which initiates spine protrusions by coupling phosphoinositide signaling, direct membrane bending, and actin assembly to ensure proper synaptogenesis.