Stasimon/Tmem41b localizes to mitochondria-associated ER membranes and is essential for mouse embryonic development

Abstract

Stasimon (also known as Tmem41b) is an evolutionarily conserved transmembrane protein first identified for its contribution to motor system dysfunction in animal models of the childhood neurodegenerative disease spinal muscular atrophy (SMA). Stasimon was shown to be required for normal neurotransmission in the motor circuit of Drosophila larvae and proper development of motor axons in zebrafish embryos as well as to suppress analogous neuronal phenotypes in SMA models of these organisms. However, the subcellular localization and molecular functions of Stasimon are poorly understood. Here, we combined immunoprecipitation with mass spectrometry to characterize the Stasimon interactome in mammalian cells, which reveals association with components of the endoplasmic reticulum (ER), mitochondria, and the COPI vesicle trafficking machinery. Expanding on the interaction results, we used subcellular fractionation studies and super-resolution microscopy to identify Stasimon as an ER-resident protein that localizes at mitochondria-associated ER membranes (MAM), functionally specialized contact sites between ER and mitochondria membranes. Lastly, through characterization of novel knockout mice, we show that Stasimon is an essential gene for mouse embryonic development. Together, these findings identify Stasimon as a novel transmembrane protein component of the MAM with an essential requirement for mammalian development.

CRISPR screening using an expanded toolkit of autophagy reporters identifies TMEM41B as a novel autophagy factor

“…On the basis of these phenotypic similarities, one immediate hypothesis is that TMEM41B and VMP1 function as a complex. Indeed, Morita and colleagues were able to isolate a VMP1/TMEM41B-containing co-complex in the presence of n-dodecyl-β-D-maltoside/cholesteryl hemisuccinate (DDM/CHS) [53], although such a complex was not observed in other detergents [54,55]. It remains an important future goal to establish whether TMEM41B’s function is dependent on its interaction with VMP1.…”

Stasimon Contributes to the Loss of Sensory Synapses and Motor Neuron Death in a Mouse Model of Spinal Muscular Atrophy

“…Recent studies have shown that Stasimon is an ER-resident, six-transmembrane-pass protein that is essential for mouse embryonic development (Van Alstyne et al, 2018b) and functions in autophagy (Moretti et al, 2018;Morita et al, 2018;Shoemaker et al, 2019). There have also been reports of autophagy dysregulation in SMA, but there is disagreement about whether this pathway is inhibited (Custer and Androphy, 2014;Periyakaruppiah et al, 2016;Rodriguez-Muela et al, 2018) or stimulated (Gonç alves et al, 2018;Piras et al, 2017) by SMN deficiency.…”

Interaction between alpha-COP and SMN ameliorates disease phenotype in a mouse model of spinal muscular atrophy

“…Stasimon is expressed at high levels in mouse neural tissues, and studies recently showed that it is expressed at point of contact between the endoplasmic reticulum (ER) and mitochondria. Over-expression of GFP-tagged Stasimon in HEK293T cells followed by immunoprecipitation identified α-COP as a Stasimon interacting protein [29]. This finding opens up the possibility that by expressing α-COP, we are impacting Stasimon function in a way that is beneficial to SMA mice, perhaps by enhancing its function at the interface between the ER and mitochondria.…”