Evolution of sociality by natural selection on variances in reproductive fitness: evidence from a social bee

Background  

The Central Limit Theorem (CLT) is a statistical principle that states that as the number of repeated samples from any population increase, the variance among sample means will decrease and means will become more normally distributed. It has been conjectured that the CLT has the potential to provide benefits for group living in some animals via greater predictability in food acquisition, if the number of foraging bouts increases with group size. The potential existence of benefits for group living derived from a purely statistical principle is highly intriguing and it has implications for the origins of sociality.     

Differences in binding behavior of (−)‐epigallocatechin gallate to β‐lactoglobulin heterodimers (AB) compared to homodimers (A) and (B)

The lipocalin β‐lactoglobulin (β‐LG) exists in different natural genetic variants—of which β‐LG A and B are predominant in bovine milk. At physiological conditions the protein dimerizes—building homodimers of β‐LG A and β‐LG B and heterodimers of β‐LG AB. Although β‐LG is one of the most intensely characterized lipocalins, the interaction behavior of ligands with hetero‐ and homodimers of β‐LG is largely unknown. The present findings revealed significant differences for hetero‐ and homodimers regarding ligand binding capacity as tested with a model ligand (i.e. surface binding (?)‐epigallocatechin gallate (EGCG)). These findings were confirmed using FT‐IR, where the addition of EGCG influenced the β‐sheet backbone of homodimer A and B with significantly higher intensity compared to heterodimer AB. Further, shape analysis by SAXS revealed oligomerization of both types of dimers upon addition of EGCG; however, homodimer A and B produced significantly larger aggregates compared to the heterodimer AB. In summary, the present study revealed that EGCG showed significantly different interaction reactivity (binding sites, aggregation size and conformational changes) to the hetero and homodimers of β‐LG in the order β‐LG A > B > AB. The results suggest that conformational differences between homodimers and heterodimers strongly influence the EGCG binding ability. This may also occur with other polyphenols and ligands of β‐LG and gives not only important information for β‐LG binding studies, but may also apply for polymorphisms of other self‐aggregating lipocalins. Copyright © 2015 John Wiley & Sons, Ltd.     

Contributions of Unique Intracellular Domains to Switchlike Biosensing by Toll-like Receptor 4

Toll-like receptors (TLRs) mediate immune recognition of both microbial infections and tissue damage. Aberrant TLR signaling promotes disease; thus, understanding the regulation of TLR signaling is of medical relevance. Although downstream mediators of TLR signaling have been identified, the detailed mechanism by which ligand binding-mediated dimerization induces downstream signaling remains poorly understood. Here, we investigate this question for TLR4, which mediates responsiveness to bacterial LPS and drives inflammatory disease. TLR4 exhibits structural and functional features that are unique among TLRs, including responsiveness to a wide variety of ligands. However, the connection between these structural features and the regulation of signaling is not clear. Here, we investigated how the unique intracellular structures of TLR4 contribute to receptor signaling. Key conclusions include the following. 1) The unique intracellular linker of TLR4 is important for achieving LPS-inducible signaling via Toll/IL-1 receptor (TIR) domain-containing adapter-inducing interferon-β (TRIF) but less so for signaling via myeloid differentiation primary response 88 (MyD88). 2) Membrane-bound TLR4 TIR domains were sufficient to induce signaling. However, introducing long, flexible intracellular linkers neither induced constitutive signaling nor ablated LPS-inducible signaling. Thus, the initiation of TLR4 signaling is regulated by a mechanism that does not require tight geometric constraints. Together, these observations necessitate refining the model of TLR4 signal initiation. We hypothesize that TLR4 may interact with an inhibitory partner in the absence of ligand, via both TIR and extracellular domains of TLR4. In this speculative model, ligand binding induces dissociation of the inhibitory partner, triggering spontaneous, switchlike TIR domain homodimerization to initiate downstream signaling.     

To be or not to be planktonic? Self‐inhibition of biofilm development

The transition between planktonic growth and biofilm formation represents a tightly regulated developmental shift that has substantial impact on cell fate. Here, we highlight different mechanisms through which bacteria limit their own biofilm development. The mechanisms involved in these self‐inhibition processes include: (i) regulation by secreted small molecules, which govern intricate signalling cascades that eventually decrease biofilm development, (ii) extracellular polysaccharides capable of modifying the physicochemical properties of the substratum and (iii) extracellular DNA that masks an adhesive structure. These mechanisms, which rely on substances produced by the bacterium and released into the extracellular milieu, suggest regulation at the communal level. In addition, we provide specific examples of environmental cues (e.g. blue light or glucose level) that trigger a cellular response reducing biofilm development. All together, we describe a diverse array of mechanisms underlying self‐inhibition of biofilm development in different bacteria and discuss possible advantages of these processes.     

FraC/FraD-dependent intercellular molecular exchange in the filaments of a heterocyst-forming cyanobacterium, Anabaena sp

The filamentous, heterocyst‐forming cyanobacteria are multicellular organisms in which two different cell types, the CO₂‐fixing vegetative cells and the N₂‐fixing heterocysts, exchange nutrients and regulators. In Anabaena sp. strain PCC 7120, inactivation of sepJ or genes in the fraC operon (fraC, fraD and fraE) produce filament fragmentation. SepJ, FraC and FraD are cytoplasmic membrane proteins located in the filament's intercellular septa that are needed for intercellular exchange of the fluorescent tracer calcein (622 Da). Transmission electron microscopy showed an alteration in the heterocyst cytoplasmic membrane at the vegetative cell‐heterocyst septa in ΔfraC and ΔfraD mutants. Immunogold labelling of FraD confirmed its localization in the intercellular septa and clearly showed the presence of part of the protein between the cytoplasmic membranes of the adjacent cells. This localization seemed to be affected in the ΔfraC mutant but was not impaired in a ΔsepJ mutant. Intercellular transfer of a smaller fluorescent tracer, 5‐carboxyfluorescein (374 Da), was largely impaired in ΔfraC, ΔfraD and double ΔfraC‐ΔfraD mutants, but much less in the ΔsepJ mutant. These results show the existence in the Anabaena filaments of a FraC/FraD‐dependent intercellular molecular exchange that does not require SepJ.     

Reduced activity of a sensory neuron during a sleep-like state in Caenorhabditis elegans

Sleep-like states occur in the life of all animals carefully studied and are characterized by reduced behavioral and neural activity as well as reduced responsiveness to stimulation [1]. How is reduced responsiveness to stimulation generated? We used calcium imaging to investigate a sleep-like state in larvae of the nematode Caenorhabditis elegans. We found that overall spontaneous neural activity was reduced during the sleep-like state in many neurons, including the mechanosensory neuron ALM. Stimulus-evoked calcium transients and behavior were reduced in ALM during the sleep-like state. Thus, reduced activity of ALM may contribute to reduce responsiveness during a sleep-like state.     

Aerosols transmit prions to immunocompetent and immunodeficient mice

Prions, the agents causing transmissible spongiform encephalopathies, colonize the brain of hosts after oral, parenteral, intralingual, or even transdermal uptake. However, prions are not generally considered to be airborne. Here we report that inbred and crossbred wild-type mice, as well as tga20 transgenic mice overexpressing PrP(C), efficiently develop scrapie upon exposure to aerosolized prions. NSE-PrP transgenic mice, which express PrP(C) selectively in neurons, were also susceptible to airborne prions. Aerogenic infection occurred also in mice lacking B- and T-lymphocytes, NK-cells, follicular dendritic cells or complement components. Brains of diseased mice contained PrP(Sc) and transmitted scrapie when inoculated into further mice. We conclude that aerogenic exposure to prions is very efficacious and can lead to direct invasion of neural pathways without an obligatory replicative phase in lymphoid organs. This previously unappreciated risk for airborne prion transmission may warrant re-thinking on prion biosafety guidelines in research and diagnostic laboratories.