Biology subjects

Carrete, L.

Publications and source records attributed to Carrete, L..

3 recordsLinked to original sources

bioRxiv2022

Intrinsically photosensitive retinal ganglion cells evade temporal filtering to encode environmental light intensity

The retina encodes environmental light intensity to drive innate physiological responses. The synaptic basis of such coding remains obscure. Intrinsically photosensitive retinal ganglion cells (ipRGCs) are the only retinal output neurons stably encoding intensity. They do so even without their melanopsin photopigment, so specializations in their synaptic drive from bipolar cells (BCs) must also contribute. Here, we shed new light on mechanisms responsible for this unique intensity-coding drive. By ultrastructural reconstruction, we show that specific BC types and unusual ribbon synapses carry photoreceptor signals to ipRGCs. By glutamate imaging and electrophysiology, we show that their light responses are unusually persistent. Still, we find that virtually all BCs encode intensity. Intensity coding becomes restricted to ipRGCs primarily because other RGCs filter out steady-state intensity signals postsynaptically. Thus, neural "pinholes" in global, persistent neural "masking" allow intensity signals to be encoded by ipRGCs and sent to specific centers of the visual brain.

neuroscience↗

bioRxiv2018

Synaptic circuits for irradiance coding by intrinsically photosensitive retinal ganglion cells

We have explored the synaptic networks responsible for the unique capacity of intrinsically photosensitive retinal ganglion cells (ipRGCs) to encode overall light intensity. This luminance signal is crucial for circadian, pupillary and related reflexive responses light. By combined glutamate-sensor imaging and patch recording of postsynaptic RGCs, we show that the capacity for intensity-encoding is widespread among cone bipolar types, including OFF types.\n\nNonetheless, the bipolar cells that drive ipRGCs appear to carry the strongest luminance signal. By serial electron microscopic reconstruction, we show that Type 6 ON cone bipolar cells are the dominant source of such input, with more modest input from Types 7, 8 and 9 and virtually none from Types 5i, 5o, 5t or rod bipolar cells. In conventional RGCs, the excitatory drive from bipolar cells is high-pass temporally filtered more than it is in ipRGCs. Amacrine-to-bipolar cell feedback seems to contribute surprisingly little to this filtering, implicating mostly postsynaptic mechanisms. Most ipRGCs sample from all bipolar terminals costratifying with their dendrites, but M1 cells avoid all OFF bipolar input and accept only ectopic ribbon synapses from ON cone bipolar axonal shafts. These are remarkable monad synapses, equipped with as many as a dozen ribbons and only one postsynaptic process.

neuroscience↗

bioRxiv2017

Patterns of genomic variation in the opportunistic pathogen Candida glabrata suggest the existence of mating and a secondary association to the human host

Candida glabrata is an opportunistic fungal pathogen that ranks as the second most common cause of systemic candidiasis. Despite its genus name, this yeast is more closely related to the model yeast Saccharomyces cerevisiae than to other Candida pathogens, and hence its ability to infect humans is thought to have emerged independently. Morover, C. glabrata has all the necessary genes to undergo a sexual cycle, but it is considered an asexual organism due to the lack of direct evidence of sexual reproduction. Here, we assessed genomic and phenotypic variation across 33 globally-distributed C. glabrata isolates. We cataloged extensive copy number variation, which particularly affects genes encoding cell-wall associated proteins, including adhesins. The observed level of genetic variation in C. glabrata is significantly larger than that found in Candida albicans. This variation is structured in seven deeply divergent clades, which show recent geographical dispersion and large within-clade genomic and phenotypic differences. We show compelling evidence of recent admixture between differentiated lineages, and of purifying selection on mating genes, which provide fist evidence for the existence of a sexual cycle in this yeast. Altogether, our data point to a recent global spread of previously genetically isolated populations and suggest that humans are only a secondary niche for this yeast.

microbiology↗