Nr. Helps et al., Interaction with protein phosphatase 1 is essential for bifocal function during the morphogenesis of the Drosophila compound eye, MOL CELL B, 21(6), 2001, pp. 2154-2164
The gene bifocal (bif), required for photoreceptor morphogenesis in the Dro
sophila compound eye, encodes a protein that is shown to interact with prot
ein phosphatase 1 (PP1) using the yeast two-hybrid system. Complex formatio
n between Bif and PPI is supported by coprecipitation of the two proteins.
Residues 992 to 995 (RVQF) in the carboxy-terminal region of Bif, which con
form to the consensus PPI-binding motif, are shown to be essential for the
interaction of Bif with PPI. The interaction of PP1 with bacterially expres
sed and endogenous Bif can be disrupted by a synthetic peptide known to blo
ck interaction of other regulatory subunits with PPI. Null bif mutants exhi
bit a rough eye phenotype, disorganized rhabdomeres (light-gathering rhodop
sin-rich microvillar membrane structures in the photoreceptor cells) and al
terations in the actin cytoskeleton. Expression of wild-type bif transgenes
resulted in significant rescue of these abnormalities. In contrast, expres
sion of transgenes encoding the Bif F995A mutant, which disrupts binding to
PP1, was unable to rescue any aspect of the bif phenotype. The results ind
icate that the PP1-Bif interaction is critical for the rescue and that a ma
jor function of Bif is to target PP1c to a specific subcellular location. T
he role of the PP1-Bif complex in modulating the organization of the actin
cytoskeleton underlying the rhabdomeres is discussed.