S1 Raw images -

<div><p>Objective</p><p>A biallelic missense mutation in mitofusin 2 (<i>MFN2</i>) causes multiple symmetric lipomatosis and partial lipodystrophy, implicating disruption of mitochondrial fusion or interaction with other organelles in adipocyte differentiation, growth and/or survival. In this study, we aimed to document the impact of loss of mitofusin 1 (<i>Mfn1</i>) or 2 (<i>Mfn2)</i> on adipogenesis in cultured cells.</p><p>Methods</p><p>We characterised adipocyte differentiation of wildtype (WT), <i>Mfn1</i><sup><i>-/-</i></sup> and <i>Mfn2</i><sup><i>-/-</i></sup> mouse embryonic fibroblasts (MEFs) and 3T3-L1 preadipocytes in which Mfn1 or 2 levels were reduced using siRNA.</p><p>Results</p><p><i>Mfn1</i><sup><i>-/-</i></sup> MEFs displayed striking fragmentation of the mitochondrial network, with surprisingly enhanced propensity to differentiate into adipocytes, as assessed by lipid accumulation, expression of adipocyte markers (<i>Plin1</i>, <i>Fabp4</i>, <i>Glut4</i>, <i>Adipoq</i>), and insulin-stimulated glucose uptake. RNA sequencing revealed a corresponding pro-adipogenic transcriptional profile including <i>Pparg</i> upregulation. <i>Mfn2</i><sup><i>-/-</i></sup> MEFs also had a disrupted mitochondrial morphology, but in contrast to <i>Mfn1</i><sup>-/-</sup> MEFs they showed reduced expression of adipocyte markers. <i>Mfn1</i> and <i>Mfn2</i> siRNA mediated knockdown studies in 3T3-L1 adipocytes generally replicated these findings.</p><p>Conclusions</p><p>Loss of <i>Mfn1</i> but not <i>Mfn2</i> in cultured pre-adipocyte models is pro-adipogenic. This suggests distinct, non-redundant roles for the two mitofusin orthologues in adipocyte differentiation.</p></div>