Caste‐specific gene expression underlying the differential adult brain development in the honeybee Apis mellifera

• Published in: Insect molecular biology Vol. 30; no. 1; pp. 42 - 56
• Main Authors: Paula Junior, D. E., Oliveira, M. T., Bruscadin, J. J., Pinheiro, D. G., Bomtorin, A. D., Coelho Júnior, V. G., Moda, L. M. R., Simões, Z. L. P., Barchuk, A. R.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.02.2021; Blackwell Publishing Ltd
• Subjects: Apis mellifera; Brain; brain development; Caspase; Castes; Developmental stages; diphenism; Gene expression; Genes; honey bee; Insulin; Larval development; Metamorphosis; nervous system; Neural coding; pupa; queen; Queens; Signal transduction; Transcription; worker; Workers (insect caste); brain development; honey bee; pupa; nervous system; queen; diphenism; worker
• ISSN: 0962-1075; 1365-2583
• DOI: 10.1111/imb.12671

Apis mellifera adult workers feature more developed key brain regions than queens, which allows them to cope with the broad range of duties they need to perform in a colony. However, at the end of larval development, the brain of queens is largely more developed than that of workers. Major morphogenetic changes take place after metamorphosis that shift caste‐specific brain development. Here, we tested the hypothesis that this phenomenon is hormonally governed and involves differential gene expression. Our molecular screening approach revealed a set of differentially expressed genes in Pp (first pharate‐adult phase) brains between castes mainly coding for tissue remodelling and energy‐converting proteins (e.g. hex 70a and ATPsynβ). An in‐depth qPCR analysis of the transcriptional behaviour during pupal and pharate‐adult developmental stage in both castes and in response to artificially augmented hormone titres of 18 genes/variants revealed that: i. subtle differences in hormone titres between castes might be responsible for the differential expression of the EcR and insulin/insulin‐like signalling (IIS) pathway genes; ii. the morphogenetic activity of the IIS in brain development must be mediated by ILP‐2, iii. which together with the tum, mnb and caspase system, can constitute the molecular effectors of the caste‐specific opposing brain developmental trajectories. A molecular screening approach revealed a set of differentially expressed genes in the first pharate‐adult phase brains between castes mainly coding for tissue remodelling and energy‐converting proteins. Subtle differences in hormone titres between castes might be responsible for the differential expression of the EcR and insulin/insulin‐like signalling (IIS) pathway genes. ILP‐2, tum, mnb and caspase genes can constitute the molecular effectors of the caste‐specific opposing brain developmental trajectories.