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Cyclophilins are ubiquitous and abundant proteins that exhibit peptidyl prolyl cis-trans isomerization (PPlase) activity in vitro. Their functions in vivo, however, are not well understood. Two new retinal cyclophilin isoforms, types I and II, are highly expressed in cone photoreceptors of the vertebrate retina. Type-II cyclophilin is identical to RanBP2, a large protein that binds the GTPase Ran. Here we report that two contiguous domains in RanBP2, Ran-binding domain 4 (RBD4) and cyclophilin, act in concert as a chaperone for the opsin molecule of the red/green-sensitive visual pigment of a dichromatic vertebrate. In Drosophila, the cyclophilin NinaA is expressed in all photoreceptors and is required for the expression of only a subset of opsins. The molecular basis of these photoreceptor class-specific effects and the functions of NinaA and other cyclophilins in vivo remain unclear. Unlike NinaA, which forms a stable complex with opsin from retinular cells R1-6, we find that the cyclophilin domain of RanBP2 does not bind opsin directly; rather, it augments and stabilizes the interaction between red/green (R/G) opsin and the RBD4 domain. This involves a cyclophilin-mediated modification of R/G opsin, possibly involving proline isomerization. The RBD4-cyclophilin supradomain of RanBP2, therefore, is a form of vertebrate chaperone of defined substrate specificity, which may be involved in the processing and/or transport of long-wavelength opsin in cone photoreceptor cells.

SUMMARY Division of labor in honey bee colonies is influenced by the foraging gene (Amfor), which encodes a cGMP-dependent protein kinase (PKG). Amfor upregulation in the bee brain is associated with the age-related transition from working in the hive to foraging for food outside, and cGMP treatment (which increases PKG activity)causes precocious foraging. We present two lines of evidence in support of the hypothesis that Amfor affects division of labor by modulating phototaxis. We first show that a subset of worker bees involved in the removal of corpses from the hive had forager-like brain levels of Amfor brain expression despite being middle aged; age-matched food-handlers, who do not leave the hive to perform their job, had low levels of Amforexpression. This finding suggests that occupations that involve working outside the hive are associated with high levels of Amfor in brain. Secondly, foragers were much more positively phototactic than hive bees in a laboratory assay, and cGMP treatment caused a precocious onset of positive phototaxis. The cGMP effect was not due to a general increase in behavioral activity; cGMP treatment had no effect on locomotor activity under either constant darkness or a light:dark regime. The cGMP effect also was not due to changes in circadian rhythmicity; cGMP treatment had no effect on age at onset of locomotor circadian rhythmicity or the period of rhythmicity. The effects of Amfor on phototaxis are not related to peripheral processing;electroretinogram analysis revealed no effect of cGMP treatment on photoreceptor activity and no differences between untreated hive bees and foragers. The cAMP/PKA pathway does not appear to be playing a similar role to cGMP/PKG in the honey bee; cAMP treatment did not affect phototaxis and gene expression analysis revealed task-related differences only for the gene encoding the regulatory subunit, but not the catalytic subunit, of PKA. Our findings implicate one neural process associated with honey bee division of labor that can be affected by naturally occurring changes in the expression of Amfor.

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