A participação de minibrain no desenvolvimento diferencial do cérebro adulto em castas de abelhas apis mellifera

Abstract

In colonies of Apis mellifera bees, there are two types of females (castes), queens (reproductive) and workers (non-reproductive). The ontogenetic trajectory leading to the emergence of queens and workers depends on the quantity and quality of the diet received during larval development. This environmental influence allows the development of caste-specific characteristics, including morphology, physiology, and behavior. The adult worker bee's brain is proportionally larger than that of queens, enabling workers to perform a range of activities necessary for maintaining colony well-being. Conversely, post-embryonic neurogenesis in A. mellifera begins early in the larval stage and is influenced by the differential nutrition received by females, resulting in queens having larger brains. Morphological analyses show that this reversal in morphogenetic tendency occurs after metamorphosis. Large-scale transcriptomic analyses using oligonucleotide microarray hybridization revealed higher transcription levels in the brains of worker pupae for 324 genes, including minibrain (mnb). This study aimed to assess the involvement of the mnb gene in the differential development of adult brains between queens and worker bees of A. mellifera. The first step was obtaining developing worker bees in the pupal stage with mnb knockdown, carrying out sequential RNAi (knockdown) experiments. Three sequential experiments were conducted, each with 150 pupae divided into 3-4 experimental groups: pupae that received injections of dsMNB, dsGFP injections, 0.9% NaCl injections, and naive pupae. After a treatment period, molecular analyses were performed to assess mnb knockdown indicators and evaluate the morphological phenotype of the brains. The qPCR results showed mnb knockdown occurrence and enabled us to analyze the timing of gene silencing. Histological tests showed the effect of knockdown on the development of the adult brain, which was evidenced by the smaller dimensions presented by brain regions such as the mushroom body, optic lobes, and brain (p< 0,05). These results indicate that mnb plays a key role in the development of the brain of workers during the pupal period and confirm its participation in the differential development of A. mellifera castes.