A Distinct Subset of Fibroblastic Stromal Cells Constitutes the Cortex-Medulla Boundary Subcompartment of the Lymph Node

The spatiotemporal regulation of immune responses in the lymph node (LN) depends on its sophisticated tissue architecture, consisting of several subcompartments supported by distinct fibroblastic stromal cells (FSCs). However, the intricate details of stomal structures and associated FSC subsets are not fully understood. Using several gene reporter mice, we sought to discover unrecognized stromal structures and FSCs in the LN. The four previously identified FSC subsets in the cortex are clearly distinguished by the expression pattern of reporters including PDGFR beta, CCL21-ser, and CXCL12. Herein, we identified a unique FSC subset expressing both CCL21-ser and CXCL12 in the deep cortex periphery (DCP) that is characterized by preferential B cell localization. This subset was clearly different from CXCL12(high) LepR(high) FSCs in the medullary cord, which harbors plasma cells. B cell localization in the DCP was controlled chiefly by CCL21-ser and, to a lesser extent, CXCL12. Moreover, the optimal development of the DCP as well as medulla requires B cells. Together, our findings suggest the presence of a unique microenvironment in the cortex-medulla boundary and offer an advanced view of the multi-layered stromal framework constructed by distinct FSC subsets in the LN

Beta-Arrestin Functionally Regulates the Non-Bleaching Pigment Parapinopsin in Lamprey Pineal

The light response of vertebrate visual cells is achieved by light-sensing proteins such as opsin-based pigments as well as signal transduction proteins, including visual arrestin. Previous studies have indicated that the pineal pigment parapinopsin has evolutionally and physiologically important characteristics. Parapinopsin is phylogenetically related to vertebrate visual pigments. However, unlike the photoproduct of the visual pigment rhodopsin, which is unstable, dissociating from its chromophore and bleaching, the parapinopsin photoproduct is stable and does not release its chromophore. Here, we investigated arrestin, which regulates parapinopsin signaling, in the lamprey pineal organ, where parapinopsin and rhodopsin are localized to distinct photoreceptor cells. We found that beta-arrestin, which binds to stimulated G protein-coupled receptors (GPCRs) other than opsin-based pigments, was localized to parapinopsin-containing cells. This result stands in contrast to the localization of visual arrestin in rhodopsin-containing cells. Beta-arrestin bound to cultured cell membranes containing parapinopsin light-dependently and translocated to the outer segments of pineal parapinopsin-containing cells, suggesting that beta-arrestin binds to parapinopsin to arrest parapinopsin signaling. Interestingly, beta-arrestin colocalized with parapinopsin in the granules of the parapinopsin-expressing cell bodies under light illumination. Because beta-arrestin, which is a mediator of clathrin-mediated GPCR internalization, also served as a mediator of parapinopsin internalization in cultured cells, these results suggest that the granules were generated light-dependently by beta-arrestin-mediated internalization of parapinopsins from the outer segments. Therefore, our findings imply that beta-arrestin-mediated internalization is responsible for eliminating the stable photoproduct and restoring cell conditions to the original dark state. Taken together with a previous finding that the bleaching pigment evolved from a non-bleaching pigment, vertebrate visual arrestin may have evolved from a “beta-like” arrestin by losing its clathrin-binding domain and its function as an internalization mediator. Such changes would have followed the evolution of vertebrate visual pigments, which generate unstable photoproducts that independently decay by chromophore dissociation

Multiple Episodes of Convergence in Genes of the Dim Light Vision Pathway in Bats

The molecular basis of the evolution of phenotypic characters is very complex and is poorly understood with few examples documenting the roles of multiple genes. Considering that a single gene cannot fully explain the convergence of phenotypic characters, we choose to study the convergent evolution of rod vision in two divergent bats from a network perspective. The Old World fruit bats (Pteropodidae) are non-echolocating and have binocular vision, whereas the sheath-tailed bats (Emballonuridae) are echolocating and have monocular vision; however, they both have relatively large eyes and rely more on rod vision to find food and navigate in the night. We found that the genes CRX, which plays an essential role in the differentiation of photoreceptor cells, SAG, which is involved in the desensitization of the photoactivated transduction cascade, and the photoreceptor gene RH, which is directly responsible for the perception of dim light, have undergone parallel sequence evolution in two divergent lineages of bats with larger eyes (Pteropodidae and Emballonuroidea). The multiple convergent events in the network of genes essential for rod vision is a rare phenomenon that illustrates the importance of investigating pathways and networks in the evolution of the molecular basis of phenotypic convergence

Adaptation of pineal expressed teleost exo-rod opsin to non-image forming photoreception through enhanced Meta II decay

Photoreception by vertebrates enables both image-forming vision and non-image-forming responses such as circadian photoentrainment. Over the recent years, distinct non-rod non-cone photopigments have been found to support circadian photoreception in diverse species. By allowing specialization to this sensory task a selective advantage is implied, but the nature of that specialization remains elusive. We have used the presence of distinct rod opsin genes specialized to either image-forming (retinal rod opsin) or non-image-forming (pineal exo-rod opsin) photoreception in ray-finned fish (Actinopterygii) to gain a unique insight into this problem. A comparison of biochemical features for these paralogous opsins in two model teleosts, Fugu pufferfish (Takifugu rubripes) and zebrafish (Danio rerio), reveals striking differences. While spectral sensitivity is largely unaltered by specialization to the pineal environment, in other aspects exo-rod opsins exhibit a behavior that is quite distinct from the cardinal features of the rod opsin family. While they display a similar thermal stability, they show a greater than tenfold reduction in the lifetime of the signaling active Meta II photoproduct. We show that these features reflect structural changes in retinal association domains of helices 3 and 5 but, interestingly, not at either of the two residues known to define these characteristics in cone opsins. Our findings suggest that the requirements of non-image-forming photoreception have lead exo-rod opsin to adopt a characteristic that seemingly favors efficient bleach recovery but not at the expense of absolute sensitivity

Bistable UV pigment in the lamprey pineal

Lower vertebrates can detect UV light with the pineal complex independently of eyes. Electrophysiological studies, together with chromophore extraction analysis, have suggested that the underlying pigment in the lamprey pineal exhibits a bistable nature, that is, reversible photoreaction by UV and visible light, which is never achieved by known UV pigments. Here we addressed the molecular identification of the pineal UV receptor. Our results showed that the long-hypothesized pigment is a lamprey homologue of parapinopsin, which exhibits an absorption maximum at 370 nm, in the UV region. UV light causes cis-trans isomerization of its retinal(2) chromophore, forming a stable photoproduct having an absorption maximum at 515 nm, in the green region. The photoproduct reverts to the original pigment upon visible light absorption, showing photoregeneration of the pigment. In situ hybridization showed that parapinopsin is selectively expressed in the cells located in the dorsal region of the pineal organ. We successfully obtained the hyperpolarizing responses with a maximum sensitivity of ≈380 nm from the photoreceptor cells at the dorsal region, in which the outer segment was clearly stained with anti-parapinopsin antibody. These results demonstrated that parapinopsin is the pineal UV pigment having photointerconvertible two stable states. The bistable nature of the parapinopsin can account for the photorecovery of the pineal UV sensitivity by background green light in the lamprey. Furthermore, we isolated the parapinopsin homologues from fish and frog pineal complexes that exhibit UV sensitivity, suggesting that parapinopsin is a common molecular basis for pineal UV reception in the vertebrate