The pigment‐dispersing factor neuronal network systematically grows in developing honey bees

• Published in: Journal of comparative neurology (1911) 2022-06, Vol.530 (9), p.1321-1340
• Main Authors: Beer, Katharina, Härtel, Stephan, Helfrich‐Förster, Charlotte
• Format: Article
• Language: English
• Subjects: Animals; Apis mellifera; Bees; Brain - metabolism; circadian clock; Circadian Clocks; Circadian rhythm; Circadian Rhythm - physiology; Circadian rhythms; Fibers; immunohistochemistry; Insecta - metabolism; Larva - metabolism; larval and pupal development; Medulla oblongata; Metamorphosis; neuroanatomy; Neurons - metabolism; Neuropeptides - metabolism; Optic Lobe, Nonmammalian - physiology; Protocerebrum
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.25278

The neuropeptide pigment‐dispersing factor (PDF) plays a prominent role in the circadian clock of many insects including honey bees. In the honey bee brain, PDF is expressed in about 15 clock neurons per hemisphere that lie between the central brain and the optic lobes. As in other insects, the bee PDF neurons form wide arborizations in the brain, but certain differences are evident. For example, they arborize only sparsely in the accessory medulla (AME), which serves as important communication center of the circadian clock in cockroaches and flies. Furthermore, all bee PDF neurons cluster together, which makes it impossible to distinguish individual projections. Here, we investigated the developing bee PDF network and found that the first three PDF neurons arise in the third larval instar and form a dense network of varicose fibers at the base of the developing medulla that strongly resembles the AME of hemimetabolous insects. In addition, they send faint fibers toward the lateral superior protocerebrum. In last larval instar, PDF cells with larger somata appear and send fibers toward the distal medulla and the medial protocerebrum. In the dorsal part of the medulla serpentine layer, a small PDF knot evolves from which PDF fibers extend ventrally. This knot disappears during metamorphosis and the varicose arborizations in the putative AME become fainter. Instead, a new strongly stained PDF fiber hub appears in front of the lobula. Simultaneously, the number of PDF neurons increases and the PDF neuronal network in the brain gets continuously more complex. Pigment‐dispersing factor (PDF) neuronal network (magenta) grows in complexity with the developing honey bee brain. Numbers of PDF neurons in the honey bee brain are displayed along with the developmental stage of the honey bee.