Endogenous Control and Reward-based Mechanisms Shape Infants' Attention Biases to Caregiver Faces.

Infants rely on developing attention skills to identify relevant stimuli in their environments. Although caregivers are socially rewarding and a critical source of information, they are also one of many stimuli that compete for infants' attention. Young infants preferentially hold attention on caregiver faces, but it is unknown whether they also preferentially orient to caregivers and the extent to which these attention biases reflect reward-based attention mechanisms. To address these questions, we measured 4- to 10-month-old infants' (N = 64) frequency of orienting and duration of looking to caregiver and stranger faces within multi-item arrays. We also assessed whether infants' attention to these faces related to individual differences in Surgency, an indirect index of reward sensitivity. Although infants did not show biased attention to caregiver versus stranger faces at the group level, infants were increasingly biased to orient to stranger faces with age and infants with higher Surgency scores showed more robust attention orienting and attention holding biases to caregiver faces. These effects varied based on the selective attention demands of the task, suggesting that infants' attention biases to caregiver faces may reflect both developing attention control skills and reward-based attention mechanisms.

Identifying novel mycobacterial stress associated genes using a random mutagenesis screen in Mycobacterium smegmatis.

Cell envelope associated components of Mycobacterium tuberculosis (M.tb) have been implicated in stress response, immune modulation and in vivo survival of the pathogen. Although many such factors have been identified, there is a large disparity between the number of genes predicted to be involved in functions linked to the envelope and those described in the literature. To identify and characterise novel stress related factors associated with the mycobacterial cell envelope, we isolated colony morphotype mutants of Mycobacterium smegmatis (M. smegmatis), based on the hypothesis that mutants with unusual colony morphology may have defects in the biosynthesis of cell envelope components. On testing their susceptibility to stress conditions relevant to M.tb physiology, multiple mutants were found to be sensitive to Isoniazid, Diamide and H2O2, indicative of altered permeability due to changes in cell envelope composition. Two mutants showed defects in biofilm formation implying possible roles for the target genes in antibiotic tolerance and/or virulence. These assays identified novel stress associated roles for several mycobacterial genes including sahH, tatB and aceE. Complementation analysis of selected mutants with the M. smegmatis genes and their M.tb homologues showed phenotypic restoration, validating their link to the observed phenotypes. A mutant carrying an insertion in fhaA encoding a forkhead associated domain containing protein, showed reduced survival in THP-1 macrophages, providing in vivo validation to this screen. Taken together, these results suggest that the M.tb homologues of a majority of the identified genes may play significant roles in the pathogenesis of tuberculosis.