Dynamin 1- and 3-Mediated Endocytosis Is Essential for the Development of a Large Central SynapseIn Vivo

Abstract

Dynamin is a large GTPase crucial for endocytosis and sustained neurotransmission, but its role in synapse development in the mammalian brain has received little attention. We addressed this question using the calyx of Held (CH), a large nerve terminal in the auditory brainstem in mice. Tissue-specific ablation of different dynamin isoforms bypasses the early lethality of conventional knock-outs and allows us to examine CH development in a native brain circuit. Individual gene deletion of dynamin 1, a primary dynamin isoform in neurons, as well as dynamin 2 and 3, did not affect CH development. However, combined tissue-specific knock-out of both dynamin 1 and 3 (cDKO) severely impaired CH formation and growth during the first postnatal week, and the phenotypes were exacerbated by further additive conditional knock-out of dynamin 2. The developmental defect of CH in cDKO first became evident on postnatal day 3 (P3), a time point when CH forms and grows abruptly. This is followed by a progressive loss of postsynaptic neurons and increased glial infiltration late in development. However, early CH synaptogenesis before protocalyx formation was not altered in cDKO. Functional maturation of synaptic transmission in the medial nucleus of the trapezoid body in cDKO was impeded during development and accompanied by an increase in the membrane excitability of medial nucleus of the trapezoid body neurons. This study provides compelling genetic evidence that CH formation requires dynamin 1-and 3-mediated endocytosis in vivo, indicating a critical role of dynamin in synaptic development, maturation, and subsequent maintenance in the mammalian brain.

Presynaptic development is controlled by the core active zone proteins CAST/ELKS

“…Based on the data presented here and our previous study at the mature calyx, which demonstrated no change in calyx morphology (Dong et al 2018), this suggests that CAST/ELKS have a developmental stage-specific regulatory role. This is in contrast to other genetic studies that manipulated calyx growth early in development by ablating either BMP1 (Xiao et al 2013) or dynamin (Fan et al 2016) and led to calyx morphology defects throughout all developmental stages. Because loss of CAST/ELKS does not impact mature calyx morphology, this suggests that pathways regulated by CAST/ELKS that control presynaptic and AZ growth may be suppressed by pathways that control calyx remodelling after the onset of hearing.…”

Proteomic Analysis of Mouse Brain Subjected to Spaceflight

“…Upregulated within grey matter, dynamin 3 (DNM3) is expressed in the dendritic spines and is primarily associated with regulating synaptic vesicle endocytosis and recycling [25][26][27]. There are three isoforms of dynamin that share about 80% overall homology and have mostly redundant roles in clathrin-mediated endocytosis and membrane fission [25,28].…”

Polarity and Competition in the Development of the Calyx of Held Terminal in the Medial Nucleus of the Trapezoid Body in the Mouse

“…These changes only became apparent after P3, when protocalyces undergo rapid growth (Fig. 11F, Hoffpauir et al, 2006;Soria Van Hoeve and Borst, 2010;Fan et al, 2016). Multiple small, vGLUT1 positive puncta persist until P8 or later in these animals, but whether these represent unique sites of innervation-like the BMP1a/b-KO-or a monoinnervated state depleted of synaptic vesicles is unknown.…”

“…Multiple small, vGLUT1 positive puncta persist until P8 or later in these animals, but whether these represent unique sites of innervation-like the BMP1a/b-KO-or a monoinnervated state depleted of synaptic vesicles is unknown. Dyn-1/3 double knockouts also maintain immature electrophysiological properties both pre-and post-synaptically: lower frequency firing, slower rise and decay times, lack of switching from tonic (sustained bursting of APs with depolarization) to phasic (one to several APs fired with depolarization) firing, and higher resting membrane potentials compared to wild type animals (Fan et al, 2016). It is unclear, however, whether these electrophysiological defects precede the developmental dysfunction in calyx growth or are a result of it.…”

“…Adapted from Kandler and Friauf, 1994;Morest K, 1968;Hoffpauir et al, 2010;and Ford et al, 2009. Adapted from Xiao et al, 2013;Lilley et al, 2014;Taschenberger et al, 2002;Rowland et al, 2000;Han et al, 2011;Toyoshima et al, 2009;Fan, Funk, and Lou, 2016;Schwenger and Kuner, 2010;Schluter et al, 2018. .…”