The insect central complex as model for heterochronic brain development—background, concepts, and tools

Abstract

The adult insect brain is composed of neuropils present in most taxa. However, the relative size, shape, and developmental timing differ between species. This diversity of adult insect brain morphology has been extensively described while the genetic mechanisms of brain development are studied predominantly in Drosophila melanogaster. However, it has remained enigmatic what cellular and genetic mechanisms underlie the evolution of neuropil diversity or heterochronic development. In this perspective paper, we propose a novel approach to study these questions. We suggest using genome editing to mark homologous neural cells in the fly D. melanogaster, the beetle Tribolium castaneum, and the Mediterranean field cricket Gryllus bimaculatus to investigate developmental differences leading to brain diversification. One interesting aspect is the heterochrony observed in central complex development. Ancestrally, the central complex is formed during embryogenesis (as in Gryllus) but in Drosophila, it arises during late larval and metamorphic stages. In Tribolium, it forms partially during embryogenesis. Finally, we present tools for brain research in Tribolium including 3D reconstruction and immunohistochemistry data of first instar brains and the generation of transgenic brain imaging lines. Further, we characterize reporter lines labeling the mushroom bodies and reflecting the expression of the neuroblast marker gene Tc-asense, respectively.Electronic supplementary materialThe online version of this article (doi:10.1007/s00427-016-0542-7) contains supplementary material, which is available to authorized users.

The ontogenetic saga of a social brain

“…The GMC is committed to differentiate into a neuron and glial cell. Type II NBs can also selfrenew or can form intermediate neural progenitors (INPs), which give rise to GMCs (Boone and Doe 2008;Homem et al 2015;Altenhein 2015;Koniszewski et al 2016).…”

“…The spatial arrangement, timing of delamination, and molecular network that specifies the NBs are strongly conserved between species (Urbach and Technau 2003;Koniszewski et al 2016). On the other hand, NBs that form specific neuropil structures, such as the MBs, differ between species in number, arrangement, and proliferation behaviour.…”

Development of the Neurochemical Architecture of the Central Complex

“…It has been proposed that the degree to which the insect central complex is elaborated in a given species is correlated with its lifestyle (Strausfeld, 2012; Koniszewski et al, 2016). Developmental studies have revealed that the intricate columnar wiring of the FB is established quite rapidly, but at stages which also vary with the lifestyle of the insect.…”

Development of the anterior visual input pathway to the Drosophila central complex

“…The central complex and its related neuropils are highly conserved among insects (Loesel et al, 2002). However, developmental studies addressing these brain compartments are rare (for a recent review, see Koniszewski et al, 2016;Boyan & Reichert, 2011). In hemimetabolan taxa all compartments of the central complex seem to be generated during the embryonic period.…”