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. 2013 May 23;9(5):e1003522. doi: 10.1371/journal.pgen.1003522

Figure 9. Network of CDF zinc transporters in intestinal cells.

Figure 9

(A) Dietary zinc moves from the intestinal lumen to the cytoplasm of intestinal cells by an undefined mechanism. High levels of cytoplasmic zinc increase transcription of ttm-1b and cdf-2. CDF-1 (green) functions in distribution; it is localized to the basolateral surface of the plasma membrane of intestinal cells and transports cytoplasmic zinc into the pseudocoelum for use by cells such as epithelia, muscles and neurons. TTM-1B (red) functions in excretion; it is localized to the apical surface of the plasma membrane of intestinal cells and transports cytoplasmic zinc into the intestinal lumen. CDF-2 (blue) functions in storage: it is localized to the membrane of gut granules, lysosome-related organelles that acquire a bilobed morphology in response to high zinc, and it transports zinc into the lumen of these organelles [30]. TTM-1A (yellow) is localized to vesicles and may also promote zinc excretion and/or sequestration. (B) A parallel negative feedback circuit promotes zinc homeostasis in intestinal cells. TTM-1B and CDF-2 proteins reduce the level of cytoplasmic zinc and promote zinc detoxification by distinct mechanisms of zinc excretion and zinc sequestration, respectively. ttm-1b and cdf-2 transcripts are both induced by high levels of cytoplasmic zinc. Mutations that reduce the activity of ttm-1 or cdf-2 cause induction of the remaining protein.