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An essential feature of eukaryotic cell division is the inheritance of organelles (1).In the case of the Golgi apparatus, studies of inheritance are providing insights into Golgi biogenesis (2).
These results demonstrate that Golgi inheritance in Strain Construction. Fluorescent protein constructs were made by using the EGFP, enhanced yellow fluorescent protein (EYFP), and enhanced cyan fluorescent protein (ECFP) genes (BD Biosciences Clontech). Fluorescence and differential interference contrast (DIC) imaging were performed essentially as described in ref. Cells that had been grown at 23°C and then fixed in formaldehyde and glutaraldehyde were flattened between a slide and coverslip, and 10 images were captured at 0.1-μm intervals along the -axis to capture all of the fluorescence in the cells.Studies of other cell types also have revealed an involvement of the ER in Golgi inheritance. These data are consistent with the cisternal maturation hypothesis, which postulates that new Golgi cisternae are nucleated by membranes exported from the ER (14).Does Golgi inheritance always require input from the ER?Surprisingly, studies of have not revealed the expected link between ER and Golgi inheritance.Here, we revisit this issue by generating mutant strains in which many of the small buds are devoid of detectable ER.In some cases, increased fluorescence was obtained by creating constructs with three tandem copies of EGFP, EYFP, or ECFP (19). Appropriate bandpass filters (Chroma Technology, Rockingham, VT) were used to visualize GFP, cyan and yellow fluorescent proteins, and Alexa 594 phalloidin. To isolate ER inheritance mutants, the haploid strain BGY418, which contains the ER marker GFP-HDEL (26), was mutagenized to 13% survival with ethyl methanesulfonate.
Temperature-sensitive clones were identified by using a rapid screening method (19).
However, the preponderance of evidence now indicates that the mitotic Golgi consists mainly of small membrane fragments that are distinct from the ER (6–8).
Yet Golgi reassembly during cytokinesis is inhibited by blocking ER export with a dominant-negative form of the Sar-1 GTPase (5, 9), possibly indicating a role for the ER in vertebrate Golgi inheritance.
Our results fit with the idea that membranes exported from the ER coalesce with vesicles derived from existing Golgi compartments to generate new Golgi cisternae.
This basic mechanism of Golgi inheritance may be conserved from yeast to vertebrate cells.
Additional experiments suggested that the actin cytoskeleton and the type V myosin Myo2p are important for late Golgi inheritance (19).