New growth-regulatory enzyme identified

Tor-Erik Rusten
Tor Erik Rusten, a postdoc in Harald Stenmark’s group has recently used the fruit fly Drosophila melanogaster to study the function of a novel enzyme, Fab1, that catalyzes phosphorylation of a specific phospholipid to yield the reaction product known as PtdIns(3,5)P2. In a paper published in Molecular Biology of the Cell (impact factor 6.52) Rusten and co-workers show that Fab1 is essential for viability.
Drosophila mutants that lack this enzyme die at the pupal stage. Moreover, organs from the fab1 mutant larvae and pupae are enlarged, indicating that Fab1 is a negative growth regulator.

Endosomes of fab1 mutants have an expanded size and accumulate the signalling molecules Notch, Wingless and Dpp. The signalling of these molecules is nevertheless normal. The results suggest that Fab1 controls late stages of endocytic trafficking at a point when signal termination has occurred. The mechanism by which Fab1 regulates growth remains a subject for further research.

Figure legend: A normal Drosophila head is shown to the left whereas a head consisting of fab1 mutant cells is shown to the right. Note the larger size of the mutant head compared with the wild-type head.
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