Biologia molecular da morfogênese diferencial inicial do cérebro em castas de abelhas Apis mellifera

Abstract

Brain development is influenced by genetic and environmental factors. The larvae of Apis mellifera queens, which are fed with large amounts of royal jelly, experience greater and faster brain development than workers. The social brain hypothesis suggests that, evolutionarily, the differences in castes in bees were promoted by morphophysiological development trade-offs in which the caste specialized in reproduction invests in the development of the ovaries, while the workers, non-reproductive, invest in the development of the brain, which has been confirmed in A. mellifera. From a genomic point of view, highly social bee species should have a higher proportion of neurogenic genes, compared to that found in Homo sapiens, whereas solitary species should have smaller proportions. The brain diphenism of A. mellifera is evident from the morphological point of view from the 4th larval stage, however, molecularly, the difference is already present in the 3rd larval stage (L3). Using next generation sequencing (RNA-Seq) we identified 60 differentially expressed genes (DEGs) in L3 brains, which must include genes primordial for castespecific brain development. The present work aimed to determine the scope of the participation of these genes in the initial differential morphogenesis of the brain between the castes and to test the social brain hypothesis among 11 species of bees. Comparative analyses of neurogenic genes among these bees (including A. mellifera), Drosophila and Homo sapiens did not reflect an association between the proportion of these genes and the level of sociality in insects. In search of the molecular determinants of differential brain morphogenesis, we validated the expression of nine DEGs (amd, amci, forked, hex70b, hex70c, hex110, mas, nt-1 and takeout) during the larval period of both castes. To determine the possible participation of miRNAs (miRNAs miR-317, miR-34 and miR-210) in the regulation of the expression of these genes, we use in silico tools and luciferase assays. All studied DEGs respond to at least one of the miRNAs, except amd. In addition, we immunolocalize the protein product of the hex110 gene and observe that it has a nuclear location. These results show that the establishment of brain dimorphism starts at L3, at which point the larval feed becomes caste-specific, through differential gene expression regulated by miRNAs miR-317, miR-34 and miR-210.