The dynamin-like protein DLP1 is essential for normal distribution and morphology of the endoplasmic reticulum and mitochondria in mammalian cells

The dynamin family of large GTPases has been implicated in vesicle formatio n from both the plasma membrane and various intracellular membrane compartm ents. The dynamin-like protein DLP1, recently identified in mammalian tissu es, has been shown to be more closely related to the yeast dynamin proteins Vps1p and Dnm1p (42%) than to the mammalian dynamins (37%). Furthermore, D LP1 has been shown to associate with punctate vesicles that are in intimate contact with microtubules and the endoplasmic reticulum (ER) in mammalian cells. To define the function of DLP1, we have transiently expressed both w ild-type: and two mutant DLP1 proteins, tagged with-green fluorescent prote in, in cultured mammalian:cells. Point mutations in the GTP-binding domain of DLP1 (K38A and D231N) dramatically changed its intracellular distributio n from punctate vesicular structures to either an aggregated,ora diffuse pa ttern. Strikingly, cells expressing DLP1 mutants or microinjected with DLP1 antibodies showed a marked reduction in ER fluorescence and a significant aggregation and tubulation:of mitochondria by immunofluorescence microscopy . Consistent with these observations, electron microscopy of DLP1 mutant ce lls revealed a striking and quantitative change in the distribution and mor phology of mitochondria and the ER. These data support very recent studies by other authors implicating DLP1 in the maintenance of mitochondrial morph ology in both yeast and mammalian cells. Furthermore, this study provides t he first evidence that a dynamin family member participates in the maintena nce and distribution of the ER. How DLP1 might participate in the biogenesi s of two presumably distinct organelle systems is discussed.