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Residual β cell function can positively affect diabetes regulation in type 1 diabetes (T1D), but details on residual β cell mass distribution in T1D is largely lacking in a whole organ context. Implementing an optical 3D imaging pipeline, we generated a complete account of the remaining β cells throughout an entire human late onset T1D pancreas at a microscopic resolution. Our data show that most of the residual β cells were present as scattered individual cells or as punctated clusters of individual β cells, spatially separated from each other and all other endocrine cell types. Compared to islet-associated β cells, extra-islet β cells appeared in a substantially higher relative abundance in the head region of the T1D pancreas. This 3D depiction of an entire T1D pancreas shows that individual β cells may be preserved and/or formed in a highly regionalized manner, potentially reflecting key aspects of disease dynamics, advocating for increased focus on extra-islet islet β cells in attempts to develop strategies for pancreatic β cell preservation in T1D.

Seasonal variation in photoperiod is an important cue that regulates changes in physiology and behavior during the anadromous lifestyle of Atlantic salmon. The parr-smolt transformation or smoltification, where fish migrate from rivers to the ocean, is promoted by an increased photoperiod in the spring. Photoperiodic information is transferred through the light-brain-pituitary axis, resulting in pituitary hormones stimulating changes related to this transition. The light environment is perceived by ocular photopigments in the rods and cones that convey image formation and via nonvisual photoreceptors entraining biological processes that synchronize with circadian and circannual light rhythms through the molecular clock mechanism. In this study, the dynamic expression of visual and nonvisual opsin genes and clock genes through smoltification were revealed by RNA sequencing. The results showed a dramatic transition of the teleost visual system by changes in expression of the tandem duplicated medium-wavelength-sensitive (mws or "green") and long-wavelength-sensitive (lws or "red") opsin genes during seawater migration, shifting the spectral sensitivity of the green opsins by up to 40 nm towards shorter wavelengths. Concomitantly, the expression of the lws opsin gene that forms a photopigment with the most extreme absorbance maximum was upregulated. Among the nonvisual opsins, the pineal-specific exorhodopsin was greatly upregulated in seawater, coinciding with an increased expression of important enzymes that dictate melatonin synthesis. Analyzing the components of the salmonid molecular clock expressed during smoltification showed that clock genes were dynamically expressed with changes in expression both related to changes in the photoperiod and the developmental transition from freshwater to seawater. The transcriptomic profile of the teleost brain through smoltification was shown to coincide with important genes that underpin the mammalian model of photoperiodism that drive summer and winter physiology, supporting common photoperiodic pathways that regulate seasonality in vertebrates.

In the nasal cavity, olfactory receptor neurons are situated in the sensory epithelium and act to transduce odor signals, whereas the respiratory epithelium is responsible for removing unwanted particles from inhaled air. Although several molecular markers have been identified to define multiple specific cell types in the sensory epithelium, less is known to indicate cells in the respiratory domain. We have recently shown that the non-visual photoreceptor opsin 3 (Opn3) is expressed in the developing olfactory region. This raised the question as to which functional role/s Opn3 might play in the nasal epithelium, as well as whether other non-visual photoreceptors may be expressed in this region. By using Opn3-eGFP and Opn5-tdTomato reporter mice in combination with Foxj1, Ker8, OMP, Sox2, and Tubb3 immunohistochemistry analyzes, our findings show that Opn3 is restricted to the olfactory sensory domain from early embryonic stages, whereas Opn5 is up-regulated in the respiratory epithelium at later developmental stages. In adulthood, Opn3 is expressed in Sox2/Ker8-positive sustentacular cells in the sensory epithelium, whereas Opn5 expression remains in the respiratory epithelium, thus indicating that these molecular markers could be used to distinguish the sensory versus respiratory epithelia. Studies of morphology and expression patterns of Foxj1, Ker8, OMP, Sox2, and Tubb3 in adult Opn3-/- and Opn5-/- mice did not reveal differences from wild-type mice. In addition, neither Opn3-/- nor Opn5-/- mice exhibited a disturbance in olfaction compared to wild-type littermates when performing a buried food test.

To facilitate the understanding of how a complex organ such as the pancreas is formed, this chapter illustrates the general anatomical dynamics of pancreas morphogenesis that occur during development in mice (and in humans where relevant). By applying recent advances in optical imaging techniques, including optical projection tomography and light sheet fluorescence microscopy (LSFM), this chapter presents a full image series demonstrating pancreatic bud formation and growth, as well as key morphological events that result in murine and human organs that are anatomically quite different. Further, it is now well established that pancreas development is governed by complex gene regulatory networks, where the timing and duration of gene expression, as well as the degree of molecular interactions are critical. Where appropriate, these key molecular determinants in inductive processes or other events are discussed in relation to pancreas organogenesis. Finally, this chapter describes the spatial and quantitative distribution of insulin as an example of pancreatic endocrine structure-function relationships, where lobular islet heterogeneity in the adult pancreata of mice and humans are evaluated and discussed.

Pancreatic islets of Langerhans play a pivotal role in regulating blood glucose homeostasis, but critical information regarding their mass, distribution and composition is lacking within a whole organ context. Here, we apply a 3D imaging pipeline to generate a complete account of the insulin-producing islets throughout the human pancreas at a microscopic resolution and within a maintained spatial 3D context. These data show that human islets are far more heterogenous than previously accounted for with regards to their size distribution and cellular make up. By deep tissue 3D imaging, this in-depth study demonstrates that 50% of the human insulin-expressing islets are virtually devoid of glucagon-producing α-cells, an observation with significant implications for both experimental and clinical research.

Detecting different wavelengths and intensities of environmental light is crucial for the survival of many animals. In response, a multiplicity of opsins (a special group of photosensitive G protein-coupled receptors), when combined with a retinal chromophore, is able to directly detect light and initiate different downstream phototransduction signaling cascades. Although avian studies from the 1930s suggested the presence of deep brain photoreceptors that could respond to seasonal changes in the light/dark cycle, it was only a few decades ago that photopigments other than those found in the visual system (i.e. rods and cones) were identified as functional photoreceptors. It is now established that several classes of non-visual photoreceptors and the photopigments they express, in lower vertebrates to higher mammals alike, can regulate a plethora of mechanisms that function outside of vision. These include the synchronization of light/dark cycles with biological/cellular rhythms of the body (i.e. photoentrainment); melanogenesis in dermal tissues; thermoregulation in adipose tissue; embryonic eye development; smooth muscle relaxation; and the development of certain cancers. These and other mechanisms have been shown, in part at least, to be controlled by the expression of three important non-visual opsin genes, namely OPN3, OPN4 and OPN5, although other vertebrate opsin classes exist, many with unknown or unclear functional roles assigned to them presently. Specifically, these three opsins have been shown to be expressed during early embryogenesis and throughout adulthood, which will be discussed here. Moreover, this review highlights recent studies that focus on several key non-image-forming functional roles of OPN3, OPN4 and OPN5, and in particular those that impact photoreception in developing structures and pathways, as well as in adulthood.

Salmonids are ideal models as many species follow a distinct developmental program from demersal eggs and a large yolk sac to hatching at an advanced developmental stage. Further, these economically important teleosts inhabit both marine- and freshwaters and experience diverse light environments during their life histories. At a genome level, salmonids have undergone a salmonid-specific fourth whole genome duplication event (Ss4R) compared to other teleosts that are already more genetically diverse compared to many non-teleost vertebrates. Thus, salmonids display phenotypically plastic visual systems that appear to be closely related to their anadromous migration patterns. This is most likely due to a complex interplay between their larger, more gene-rich genomes and broad spectrally enriched habitats; however, the molecular basis and functional consequences for such diversity is not fully understood. This study used advances in genome sequencing to identify the repertoire and genome organization of visual opsin genes (those primarily expressed in retinal photoreceptors) from six different salmonids [Atlantic salmon (Salmo salar), brown trout (Salmo trutta), Chinook salmon (Oncorhynchus tshawytcha), coho salmon (Oncorhynchus kisutch), rainbow trout (Oncorhynchus mykiss), and sockeye salmon (Oncorhynchus nerka)] compared to the northern pike (Esox lucius), a closely related non-salmonid species. Results identified multiple orthologues for all five visual opsin classes, except for presence of a single short-wavelength-sensitive-2 opsin gene. Several visual opsin genes were not retained after the Ss4R duplication event, which is consistent with the concept of salmonid rediploidization. Developmentally, transcriptomic analyzes of Atlantic salmon revealed differential expression within each opsin class, with two of the long-wavelength-sensitive opsins not being expressed before first feeding. Also, early opsin expression in the retina was located centrally, expanding dorsally and ventrally as eye development progressed, with rod opsin being the dominant visual opsin post-hatching. Modeling by spectral tuning analysis and atomistic molecular simulation, predicted the greatest variation in the spectral peak of absorbance to be within the Rh2 class, with a ∼40 nm difference in λmax values between the four medium-wavelength-sensitive photopigments. Overall, it appears that opsin duplication and expression, and their respective spectral tuning profiles, evolved to maximize specialist color vision throughout an anadromous lifecycle, with some visual opsin genes being lost to tailor marine-based vision.

Despite lizards using a wide range of colour signals, the limited variation in photoreceptor spectral sensitivities across lizards suggests only weak selection for species-specific, spectral tuning of photoreceptors. Some species, however, have enhanced short-wavelength sensitivity, which probably helps with the detection of signals rich in ultraviolet and short wavelengths. In this study, we examined the visual system of Tiliqua rugosa, which has an ultraviolet/blue tongue, to gain insight into this species' visual ecology. We used electroretinograms, opsin sequencing and immunohistochemical labelling to characterize whole-eye spectral sensitivity and the elements that shape it. Our findings reveal that T. rugosa expresses all five opsins typically found in lizards (SWS1, SWS2, RH1, RH2 and LWS) but possesses greatly enhanced short-wavelength sensitivity compared with other diurnal lizards. This enhanced short-wavelength sensitivity is characterized by a broadening of the spectral sensitivity curve of the eye towards shorter wavelengths while the peak sensitivity of the eye at longer wavelengths (560 nm) remains similar to that of other diurnal lizards. While an increased abundance of SWS1 photoreceptors is thought to mediate elevated ultraviolet sensitivity in a couple of other lizard species, SWS1 photoreceptor abundance remains low in this species. Instead, our findings suggest that short-wavelength sensitivity is driven by multiple factors which include a potentially red-shifted SWS1 photoreceptor and the absence of short-wavelength-absorbing oil droplets. Examining the coincidence of enhanced short-wavelength sensitivity with blue tongues among lizards of this genus will provide further insight into the co-evolution of conspecific signals and whole-eye spectral sensitivity.

Light cues vary along the axis of periodicity, intensity and spectrum and perception of light is dependent on the photoreceptive capacity encoded within the genome and the opsins expressed. A global approach was taken to analyze the photoreceptive capacity and the effect of differing light conditions on a developing teleost prior to first feeding. The transcriptomes of embryos and alevins of Atlantic salmon (Salmo salar) exposed to different light conditions were analyzed, including a developmental series and a circadian profile. The results showed that genes mediating nonvisual photoreception are present prior to hatching when the retina is poorly differentiated. The clock genes were expressed early, but the circadian profile showed that only two clock genes were significantly cycling before first feeding. Few genes were differentially expressed between day and night within a light condition; however, many genes were significantly different between light conditions, indicating that light environment has an impact on the transcriptome during early development. Comparing the transcriptome data from constant conditions to periodicity of white light or different colors revealed overrepresentation of genes related to photoreception, eye development, muscle contraction, degradation of metabolites and cell cycle among others, and in constant light, several clock genes were upregulated. In constant white light and periodicity of green light, genes associated with DNA replication, chromatin remodeling, cell division and DNA repair were downregulated. The study implies a direct influence of light conditions on the transcriptome profile at early developmental stages, by a complex photoreceptive system where few clock genes are cycling.