Pigment-Dispersing Factor-expressing neurons convey circadian information in the honey bee brain.

Katharina Beer,Noa B Kahana,Charlotte Helfrich-Förster,Nadav Yayon,Pamela Menegazzi,Guy Bloch,Esther Kolbe,Ron Weiss

doi:10.1098/rsob.170224

Abstract

Pigment-Dispersing Factor (PDF) is an important neuropeptide in the brain circadian network of Drosophila and other insects, but its role in bees in which the circadian clock influences complex behaviour is not well understood. We combined high-resolution neuroanatomical characterizations, quantification of PDF levels over the day and brain injections of synthetic PDF peptide to study the role of PDF in the honey bee Apis mellifera. We show that PDF co-localizes with the clock protein Period (PER) in a cluster of laterally located neurons and that the widespread arborizations of these PER/PDF neurons are in close vicinity to other PER-positive cells (neurons and glia). PDF-immunostaining intensity oscillates in a diurnal and circadian manner with possible influences for age or worker task on synchrony of oscillations in different brain areas. Finally, PDF injection into the area between optic lobes and the central brain at the end of the subjective day produced a consistent trend of phase-delayed circadian rhythms in locomotor activity. Altogether, these results are consistent with the hypothesis that PDF is a neuromodulator that conveys circadian information from pacemaker cells to brain centres involved in diverse functions including locomotion, time memory and sun-compass orientation.

Highlights

The remarkable time memory (Zeitgedachtnis) of foraging honey bees (Apis mellifera) was one of the first lines of evidence for the functional significance of the endogenous circadian clock [1,2]
Pigment-Dispersing Factor (PDF) co-localizes with PER in the lateral neurons 2 (LN2) cluster that in foragers consists on average of 15.2 (+0.4) neurons (n 1⁄4 16, all brains sampled at one time point with high PDF levels) with rather large somata
The experiments summarized above lend credence to the hypothesis that PDF neurons in the honey bee brain fulfil the required anatomical prerequisites to convey rhythmic signals to other brain regions, including those involved in time-associative memory and time-compensated suncompass orientation

Summary

Introduction

The remarkable time memory (Zeitgedachtnis) of foraging honey bees (Apis mellifera) was one of the first lines of evidence for the functional significance of the endogenous circadian clock [1,2]. In time-compensated sun-compass orientation, forager bees use the circadian clock to compensate for the movement of the sun across the sky over the course of the day [5,6]. The time-compensated sun-compass is important for waggle dance communication, in which honey bee workers refer to the sun position in the sky when recruiting nestmates to newly discovered floral patches or nesting cavities [7]. Neurons that express the neuropeptide ‘Pigment-Dispersing Factor’ (PDF) play crucial roles in the clock network of many insects and, due to their global branching pattern in the insect brain, are suitable candidates to provide time-information to these centres.

Methods

Results

Conclusion