FOXR1 regulates stress response pathways and is necessary for proper brain development.

The forkhead box (Fox) family of transcription factors are highly conserved and play essential roles in a wide range of cellular and developmental processes. We report an individual with severe neurological symptoms including postnatal microcephaly, progressive brain atrophy and global developmental delay associated with a de novo missense variant (M280L) in the FOXR1 gene. At the protein level, M280L impaired FOXR1 expression and induced a nuclear aggregate phenotype due to protein misfolding and proteolysis. RNAseq and pathway analysis showed that FOXR1 acts as a transcriptional activator and repressor with central roles in heat shock response, chaperone cofactor-dependent protein refolding and cellular response to stress pathways. Indeed, FOXR1 expression is increased in response to cellular stress, a process in which it directly controls HSPA6, HSPA1A and DHRS2 transcripts. The M280L mutant compromises FOXR1's ability to respond to stress, in part due to impaired regulation of downstream target genes that are involved in the stress response pathway. Quantitative PCR of mouse embryo tissues show Foxr1 expression in the embryonic brain. Using CRISPR/Cas9 gene editing, we found that deletion of mouse Foxr1 leads to a severe survival deficit while surviving newborn Foxr1 knockout mice have reduced body weight. Further examination of newborn Foxr1 knockout brains revealed a decrease in cortical thickness and enlarged ventricles compared to littermate wild-type mice, suggesting that loss of Foxr1 leads to atypical brain development. Combined, these results suggest FOXR1 plays a role in cellular stress response pathways and is necessary for normal brain development.

Behavioral Performance and Neural Systems Are Robust to Sensory Injury in Workers of the Ant Pheidole dentata.

Miniaturized nervous systems have been thought to limit behavioral ability, and animals with miniaturized brains may be less flexible when challenged by injuries resulting in sensory deficits that impact the development, maintenance, and plasticity of small-scale neural networks. We experimentally examined how injuries to sensory structures critical for olfactory ability affect behavioral performance in workers of the ant Pheidole dentata, which have minute brains (0.01 mm3) and primarily rely on the perception and processing of chemical signals and cues to direct their social behavior. We employed unilateral antennal denervation to decrease the olfactory perception ability of workers and quantified consequential neuroanatomical and behavioral performance effects. Postablation neuroanatomical metrics revealed a 25% reduction in the volume of the antennal lobe ipsilateral to the antennal lesion relative to the contralateral lobe, indicating atrophy of the input-deprived tissue. However, antennectomy did not affect the volumes of the mushroom body or its subcompartments or the number of mushroom body synaptic complexes (microglomeruli) in either brain hemisphere. Synapsin immunoreactivity, however, was significantly higher in the ipsilateral mushroom body calyces, which could reflect presynaptic potentiation and homeostatic compensation in higher-order olfactory regions. Despite tissue loss caused by antennal lesioning and resulting unilateral sensory deprivation, the ability of workers to perform behaviors that encompass the breadth of their task repertoire and meet demands for colony labor remained largely intact. The few behavioral deficits recorded were restricted to pheromone trail-following ability, a result that was expected due to the need for bilateral olfactory input to process spatial odor information. Our macroscopic and cellular neuroanatomical measurements and assessments of task performance demonstrate that the miniaturized brains of P. dentata workers and their sensorimotor functions are remarkably robust to injury-related size reduction and remain capable of generating behaviors required to respond appropriately to chemical social signals and effectively nurse immatures, as well as participate in coordinated foraging.