Richter, D. | bioRxiv Science

bioRxiv2017

The ancestral animal genetic toolkit revealed by diverse choanoflagellate transcriptomes

The changes in gene content that preceded the origin of animals can be reconstructed by comparison with their sister group, the choanoflagellates. However, only two choanoflagellate genomes are currently available, providing poor coverage of their diversity. We sequenced transcriptomes of 19 additional choanoflagellate species to produce a comprehensive reconstruction of the gains and losses that shaped the ancestral animal gene repertoire. We find roughly 1,700 gene families with origins on the animal stem lineage, of which only a core set of 36 are conserved across animals. We find more than 350 gene families that were previously thought to be animal-specific actually evolved before the animal-choanoflagellate divergence, including Notch and Delta, Toll-like receptors, and glycosaminoglycan hydrolases that regulate animal extracellular matrix (ECM). In the choanoflagellate Salpingoeca helianthica, we show that a glycosaminoglycan hydrolase modulates rosette colony size, suggesting a link between ECM regulation and morphogenesis in choanoflagellates and animals.\n\nData AvailabilityRaw sequencing reads: NCBI BioProject PRJNA419411 (19 choanoflagellate transcriptomes), PRJNA420352 (S. rosetta polyA selection test)\n\nTranscriptome assemblies, annotations, and gene families: https://dx.doi.org/10.6084/m9.figshare.5686984\n\nProtocols: https://dx.doi.org/10.17504/protocols.io.kwscxee

evolutionary biology↗

bioRxiv2017

Suppressed sensory response to predictable object stimuli throughout the ventral visual stream

Prediction plays a crucial role in perception, as prominently suggested by predictive coding theories. However, the exact form and mechanism of predictive modulations of sensory processing remain unclear, with some studies reporting a downregulation of the sensory response for predictable input, while others observed an enhanced response. In a similar vein, downregulation of the sensory response for predictable input has been linked to either sharpening or dampening of the sensory representation, which are opposite in nature. In the present study we set out to investigate the neural consequences of perceptual expectation of object stimuli throughout the visual hierarchy, using fMRI in human volunteers. Participants (n=24) were exposed to pairs of sequentially presented object images in a statistical learning paradigm, in which the first object predicted the identity of the second object. Image transitions were not task relevant; thus all learning of statistical regularities was incidental. We found strong suppression of neural responses to expected compared to unexpected stimuli throughout the ventral visual stream, including primary visual cortex (V1), lateral occipital complex (LOC), and anterior ventral visual areas. Expectation suppression in LOC, but not V1, scaled positively with image preference, lending support to the dampening account of expectation suppression in object perception.\n\nSignificance StatementStatistical regularities permeate our world and help us to perceive and understand our surroundings. It has been suggested that the brain fundamentally relies on predictions and constructs models of the world in order to make sense of sensory information. Previous research on the neural basis of prediction has documented expectation suppression, i.e. suppressed responses to expected compared to unexpected stimuli. In the present study we queried the presence and characteristics of expectation suppression throughout the ventral visual stream. We demonstrate robust expectation suppression in the entire ventral visual pathway, and underlying this suppression a dampening of the sensory representation in object-selective visual cortex, but not in primary visual cortex. Taken together, our results provide novel evidence in support of theories conceptualizing perception as an active inference process, which selectively dampens cortical representations of predictable objects. This dampening may support our ability to automatically filter out irrelevant, predictable objects.

neuroscience↗