Golgi biogenesis in Toxoplasma gondii

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Abstract
Two models have been put forward to explain the growth of new Golgi during the cell cycle. The first suggests that a new Golgi grows out of the endoplasmic reticulum by de novo synthesis1. The second suggests that a pre-existing Golgi is needed for the growth of a new one, that is, the Golgi is an autonomously replicating organelle2. To resolve this issue, we have exploited the simplicity of the apicomplexan parasite Toxoplasma gondii3, which has only a single Golgi stack4. Here we show, by using video fluorescence microscopy and three-dimensional reconstructions of serial thin sections, that the Golgi grows by a process of lateral extension followed by medial fission. Further fission leads to the inheritance by each daughter of a pair of Golgi structures, which then coalesce to re-form a single Golgi. Our results indicate that new Golgi grow by autonomous duplication and raise the possibility that the Golgi is a paired structure that is analogous to centrioles5.