Project description:BACKGROUND:The diversity of visual systems in fish has long been of interest for evolutionary biologists and neurophysiologists, and has recently begun to attract the attention of molecular evolutionary geneticists. Several recent studies on the copy number and genomic organization of visual pigment proteins, the opsins, have revealed an increased opsin diversity in fish relative to most vertebrates, brought about through recent instances of opsin duplication and divergence. However, for the subfamily of opsin genes that mediate vision at the long-wavelength end of the spectrum, the LWS opsins, it appears that most fishes possess only one or two loci, a value comparable to most other vertebrates. Here, we characterize the LWS opsins from cDNA of an individual guppy, Poecilia reticulata, a fish that is known exhibit variation in its long-wavelength sensitive visual system, mate preferences and colour patterns. RESULTS:We identified six LWS opsins expressed within a single individual. Phylogenetic analysis revealed that these opsins descend from duplication events both pre-dating and following the divergence of the guppy lineage from that of the bluefin killifish, Lucania goodei, the closest species for which comparable data exists. Numerous amino acid substitutions exist among these different LWS opsins, many at sites known to be important for visual pigment function, including spectral sensitivity and G-protein activation. Likelihood analyses using codon-based models of evolution reveal significant changes in selective constraint along two of the guppy LWS opsin lineages. CONCLUSION:The guppy displays an unusually high number of LWS opsins compared to other fish, and to vertebrates in general. Observing both substitutions at functionally important sites and the persistence of lineages across species boundaries suggests that these opsins might have functionally different roles, especially with regard to G-protein activation. The reasons why are currently unknown, but may relate to aspects of the guppy's behavioural ecology, in which both male colour patterns and the female mate preferences for these colour patterns experience strong, highly variable selection pressures.

Project description:The brain executes control of nearly all bodily functions via spinal projecting neurons (SPNs) that carry command signals from numerous supraspinal regions to the spinal cord. Despite their physiological and clinical relevance, a comprehensive molecular characterization of SPNs is still lacking. Here, we use retrograde labeling, whole-brain imaging, and high-throughput transcriptional profiling to generate a unified brain-wide anatomic and transcriptomic atlas of adult mouse SPNs at single-cell resolution. We transcriptionally profiled a total of 65,002 SPNs, identified 76 region-specific SPN types, and mapped these types into a companion atlas of the whole mouse brain generated by the Allen Institute for Brain Science within the BRAIN Initiative Cell Census Network (BICCN). This SPN taxonomy reveals a three-component organization of SPNs: (1) molecularly homogeneous excitatory SPNs from the cortex, red nucleus, and cerebellum with somatotopic spinal terminations suitable for point-to-point communication; (2) highly heterogeneous excitatory and inhibitory populations in the reticular formation with broad spinal termination patterns, thus suitable for relaying commands related to the activities of the entire spinal cord; and (3) modulatory neurons expressing slow-acting neurotransmitters and/or neuropeptides in the hypothalamus, midbrain, and reticular formation for gain control of brain-spinal signals. Within each of these components, this atlas revealed additional insights. From components (2) and (3), we discovered a LIM homeobox transcription factor code that parcellates the most transcriptionally complex population, reticulospinal neurons, into five molecularly distinct and spatially segregated populations. For neurons in component (1), we found transcriptional signatures of a subset of SPNs with large soma size and correlated these with fast-firing electrophysiological properties; thus, at least two different cable lines (namely, Pvalb/Kcng4/Spp1 positive and negative) with different electrophysiological properties might underlie the transmission of brain signals to the spinal cord. Together, by integrating the anatomy, molecular identity, and physiological properties, this study establishes a comprehensive taxonomy of brain-wide SPNs and provides insight into the functional organization of SPNs in mediating brain control of bodily functions.

Dataset Information

The non-visual opsins expressed in deep brain neurons projecting to the retina in lampreys.

Publications

The non-visual opsins expressed in deep brain neurons projecting to the retina in lampreys.

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