Canalized gene expression during development mediates caste differentiation in ants.

Ant colonies are higher-level organisms consisting of specialized reproductive and non-reproductive individuals that differentiate early in development, similar to germ-soma segregation in bilateral Metazoa. Analogous to diverging cell lines, developmental differentiation of individual ants has often been considered in epigenetic terms but the sets of genes that determine caste phenotypes throughout larval and pupal development remain unknown. Here, we reconstruct the individual developmental trajectories of two ant species, Monomorium pharaonis and Acromyrmex echinatior, after obtaining >1,400 whole-genome transcriptomes. Using a new backward prediction algorithm, we show that caste phenotypes can be accurately predicted by genome-wide transcriptome profiling. We find that caste differentiation is increasingly canalized from early development onwards, particularly in germline individuals (gynes/queens) and that the juvenile hormone signalling pathway plays a key role in this process by regulating body mass divergence between castes. We quantified gene-specific canalization levels and found that canalized genes with gyne/queen-biased expression were enriched for ovary and wing functions while canalized genes with worker-biased expression were enriched in brain and behavioural functions. Suppression in gyne larvae of Freja, a highly canalized gyne-biased ovary gene, disturbed pupal development by inducing non-adaptive intermediate phenotypes between gynes and workers. Our results are consistent with natural selection actively maintaining canalized caste phenotypes while securing robustness in the life cycle ontogeny of ant colonies.

A single-cell transcriptomic atlas tracking the neural basis of division of labour in an ant superorganism.

Ant colonies with permanent division of labour between castes and highly distinct roles of the sexes have been conceptualized to be superorganisms, but the cellular and molecular mechanisms that mediate caste/sex-specific behavioural specialization have remained obscure. Here we characterized the brain cell repertoire of queens, gynes (virgin queens), workers and males of Monomorium pharaonis by obtaining 206,367 single-nucleus transcriptomes. In contrast to Drosophila, the mushroom body Kenyon cells are abundant in ants and display a high diversity with most subtypes being enriched in worker brains, the evolutionarily derived caste. Male brains are as specialized as worker brains but with opposite trends in cell composition with higher abundances of all optic lobe neuronal subtypes, while the composition of gyne and queen brains remained generalized, reminiscent of solitary ancestors. Role differentiation from virgin gynes to inseminated queens induces abundance changes in roughly 35% of cell types, indicating active neurogenesis and/or programmed cell death during this transition. We also identified insemination-induced cell changes probably associated with the longevity and fecundity of the reproductive caste, including increases of ensheathing glia and a population of dopamine-regulated Dh31-expressing neurons. We conclude that permanent caste differentiation and extreme sex-differentiation induced major changes in the neural circuitry of ants.

Chromatin accessibility and transcriptome landscapes of Monomorium pharaonis brain.

The emergence of social organization (eusociality) is a major event in insect evolution. Although previous studies have investigated the mechanisms underlying caste differentiation and social behavior of eusocial insects including ants and honeybees, the molecular circuits governing sociality in these insects remain obscure. In this study, we profiled the transcriptome and chromatin accessibility of brain tissues in three Monomorium pharaonis ant castes: queens (including mature and un-mated queens), males and workers. We provide a comprehensive dataset including 16 RNA-sequencing and 16 assay for transposase accessible chromatin (ATAC)-sequencing profiles. We also demonstrate strong reproducibility of the datasets and have identified specific genes and open chromatin regions in the genome that may be associated with the social function of these castes. Our data will be a valuable resource for further studies of insect behaviour, particularly the role of brain in the control of eusociality.

Alginate-chitosan coated layered double hydroxide nanocomposites for enhanced oral vaccine delivery.

Layered double hydroxide nanoparticles (LDHs) have shown the excellent capability and good adjuvant function as a nanocarrier for protein antigen delivery to enhance the immune response. Furthermore, LDHs have good biocompatibility and low cytotoxicity. However, their oral vaccine delivery efficiency is limited due to acidic/enzyme degradation in the stomach and low bioavailability in the small intestine. To overcome these challenges, alginate-chitosan coated LDHs nanocomposites (ALG-CHT-LDH) have been developed and used as a carrier for oral protein vaccine delivery. The physicochemical properties of ALG-CHT-LDH have been determined by dynamic light scattering (DLS), transmission electron microscopy (TEM), and ultraviolet visible (UV-Vis) spectroscopy. Protein release properties of LDHs with/without polymer coating have been investigated at various pHs. The protein release profile of ALG-CHT-LDH nanocomposites indicated that ALG-CHT coating could partially protect protein release at the acidic condition (pH 1.2). The cellular uptake efficiency of protein delivered by ALG-CHT-LDH for the intestine cells and macrophages were studied. After alginate layer falls from ALG-CHT-LDH nanocomposite, flow cytometry analysis (FACS) data suggest that chitosan-coated LDHs significantly enhance the internalization of proteins at the Caco2 and macrophage cells.