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Cell Oct 2021Being able to precisely turn on or off particular neurons in the brain at will was a major challenge for the neuroscience field, and few could have anticipated that the...
Being able to precisely turn on or off particular neurons in the brain at will was a major challenge for the neuroscience field, and few could have anticipated that the solution would come from algae. The 2021 Albert Lasker Basic Medical Research Award recognizes the contributions of Peter Hegemann, Dieter Oesterhelt, and Karl Deisseroth for their discovery of light-sensitive microbial proteins that can activate or silence brain cells. Cell editor Nicole Neuman had a conversation with Peter Hegemann about his role in bridging the two fields of microbial phototaxis and neuroscience and his perspective on the nature and future of interdisciplinary science. Excerpts from this conversation are presented below, and the full conversation is available with the article online.
Topics: Awards and Prizes; Bacterial Proteins; Bacteriorhodopsins; Channelrhodopsins; Humans; Light; Optogenetics
PubMed: 34562361
DOI: 10.1016/j.cell.2021.08.009 -
Advances in Experimental Medicine and... 2017Motile microorganisms such as the green Euglena gracilis use a number of external stimuli to orient in their environment. They respond to light with photophobic... (Review)
Review
Motile microorganisms such as the green Euglena gracilis use a number of external stimuli to orient in their environment. They respond to light with photophobic responses, photokinesis and phototaxis, all of which can result in accumulations of the organisms in suitable habitats. The light responses operate synergistically with gravitaxis, aerotaxis and other responses. Originally the microscopically obvious stigma was thought to be the photoreceptor, but later the paraxonemal body (PAB, paraflagellar body) has been identified as the light responsive organelle, located in the trailing flagellum inside the reservoir. The stigma can aid in light direction perception by shading the PAB periodically when the cell rotates helically in lateral light, but stigmaless mutants can also orient with respect to the light direction, and negative phototaxis does not need the presence of the stigma. The PAB is composed of dichroically oriented chromoproteins which is reflected in a pronounced polarotaxis in polarized light. There was a long debate about the potential photoreceptor molecule in Euglena, including carotenoids, flavins and rhodopsins. This discussion was terminated by the unambiguous proof that the photoreceptor is a 400 kDa photoactivated adenylyl cyclase (PAC) which consists of two α- and two β-subunits each. Each subunit possesses two BLUF (Blue Light receptor Using FAD) domains binding FAD, which harvest the light energy, and two adenylyl cyclases, which produce cAMP from ATP. The cAMP has been found to activate one of the five protein kinase s found in Euglena (PK.4). This enzyme in turn is thought to phosphorylate proteins inside the flagellum which result in a change in the flagellar beating pattern and thus a course correction of the cell. The involvements of PAC and protein kinase have been confirmed by RNA interference (RNAi). PAC is responsible for step-up photophobic responses as well as positive and negative phototaxis, but not for the step-down photophobic response, even though the action spectrum of this resembles those for the other two responses. Analysis of several colorless Euglena mutants and the closely related Euglena longa (formerly Astasia longa) confirms the results. Photokinesis shows a completely different action spectrum. Some other Euglena species, such as E. sanguinea and the gliding E. mutabilis, have been investigated, again showing totally different action spectra for phototaxis and photokinesis as well as step-up and step-down photophobic responses.
Topics: Euglena gracilis; Flagella; Organelles; Phototaxis; Protozoan Proteins
PubMed: 28429324
DOI: 10.1007/978-3-319-54910-1_11 -
Current Opinion in Plant Biology Jun 2017Cyanobacteria are able to move directly towards or away from a light source, a process called phototaxis. Recent studies have revealed that the spherical unicellular... (Review)
Review
Cyanobacteria are able to move directly towards or away from a light source, a process called phototaxis. Recent studies have revealed that the spherical unicellular cyanobacterium Synechocystis sp. PCC 6803 exhibits a cell polarity in response to unidirectional illumination and that micro-optic properties of cyanobacterial cells are the basis of their directional light sensing. Further functional and physiological studies highlight a very complex control of cyanobacterial phototaxis by sensory proteins, histidine kinases and response regulators. Notably, PATAN domain response regulators appear to participate in directional control of phototaxis in the cyanobacterium Synechocystis sp. PCC 6803. In this review we explain the problem of directional light sensing at the small scale of bacteria and discuss our current understanding of signal transduction in cyanobacterial phototaxis.
Topics: Bacterial Proteins; Cyanobacteria; Light; Phototaxis; Signal Transduction; Synechocystis
PubMed: 28472718
DOI: 10.1016/j.pbi.2017.03.018 -
Animal Cognition Nov 2023Light provides a widely abundant energy source and valuable sensory cue in nature. Most animals exposed to light have photoreceptor cells and in addition to eyes, there... (Review)
Review
Light provides a widely abundant energy source and valuable sensory cue in nature. Most animals exposed to light have photoreceptor cells and in addition to eyes, there are many extraocular strategies for light sensing. Here, we review how these simpler forms of detecting light can mediate rapid behavioural responses in animals. Examples of these behaviours include photophobic (light avoidance) or scotophobic (shadow) responses, photokinesis, phototaxis and wavelength discrimination. We review the cells and response mechanisms in these forms of elementary light detection, focusing on aquatic invertebrates with some protist and terrestrial examples to illustrate the general principles. Light cues can be used very efficiently by these simple photosensitive systems to effectively guide animal behaviours without investment in complex and energetically expensive visual structures.
Topics: Animals; Photoreceptor Cells; Eye; Light
PubMed: 37650997
DOI: 10.1007/s10071-023-01818-6 -
Archives of Biochemistry and Biophysics Jan 2021The lipid composition impacts directly on the structure and function of the cytoplasmic as well as organelle membranes. Depending on the type of membrane, specific... (Review)
Review
The lipid composition impacts directly on the structure and function of the cytoplasmic as well as organelle membranes. Depending on the type of membrane, specific lipids are required to accommodate, intercalate, or pack membrane proteins to the proper functioning of the cells/organelles. Rather than being only a physical barrier that separates the inner from the outer spaces, membranes are responsible for many biochemical events such as cell-to-cell communication, protein-lipid interaction, intracellular signaling, and energy storage. Photochemical reactions occur naturally in many biological membranes and are responsible for diverse processes such as photosynthesis and vision/phototaxis. However, excessive exposure to light in the presence of absorbing molecules produces excited states and other oxidant species that may cause cell aging/death, mutations and innumerable diseases including cancer. At the same time, targeting key compartments of diseased cells with light can be a promising strategy to treat many diseases in a clinical procedure called Photodynamic Therapy. Here we analyze the relationships between membrane alterations induced by photo-oxidation and the biochemical responses in mammalian cells. We specifically address the impact of photosensitization reactions in membranes of different organelles such as mitochondria, lysosome, endoplasmic reticulum, and plasma membrane, and the subsequent responses of eukaryotic cells.
Topics: Animals; Cell Membrane; Humans; Light; Oxidation-Reduction
PubMed: 33159891
DOI: 10.1016/j.abb.2020.108665 -
Chemical Reviews Nov 2018Early research on the four microbial rhodopsins discovered in the archaeal Halobacterium salinarum revealed a structural template that served as a scaffold for two... (Review)
Review
Early research on the four microbial rhodopsins discovered in the archaeal Halobacterium salinarum revealed a structural template that served as a scaffold for two different functions: light-driven ion transport and phototaxis. Bacteriorhodopsin and halorhodopsin are proton and chloride pumps, respectively, while sensory rhodopsin I and II are responsible for phototactic behavior of the archaea. Halorhodopsins have been identified in various other species. Besides this group of archaeal halorhodopsins distinct chloride transporting rhodopsins groups have recently been identified in other organism like Flavobacteria or Cyanobacteria. Halorhodopsin from Natronomonas pharaonis is the best-studied homologue because of its facile expression and purification and its advantageous properties, which was the reason to introduce this protein as neural silencer into the new field of optogenetics. Two other major families of genetically encoded silencing proteins, proton pumps and anion channels, extended the repertoire of optogenetic tools. Here, we describe the functional and structural characteristics of halorhodopsins. We will discuss the data in light of common principles underlying the mechanism of ion pumps and sensors and will review biophysical and biochemical aspects of neuronal silencers.
Topics: Animals; Bacteriorhodopsins; Binding Sites; Biological Transport; Halorhodopsins; Humans; Models, Molecular; Optogenetics; Photochemical Processes; Protein Conformation
PubMed: 29882660
DOI: 10.1021/acs.chemrev.7b00715 -
Microorganisms Mar 2022In this review, the general background is provided on cyanobacteria, including morphology, cell membrane structure, and their photosynthesis pathway. The presence of... (Review)
Review
In this review, the general background is provided on cyanobacteria, including morphology, cell membrane structure, and their photosynthesis pathway. The presence of cyanobacteria in nature, and their industrial applications are discussed, and their production of secondary metabolites are explained. Biofilm formation, as a common feature of microorganisms, is detailed and the role of cell diffusion in bacterial colonization is described. Then, the discussion is narrowed down to cyanobacterium , as a lab model microorganism. In this relation, the morphology of is discussed and its different elements are detailed. Type IV pili, the complex multi-protein apparatus for motility and cell-cell adhesion in is described and the underlying function of its different elements is detailed. The phototaxis behavior of the cells, in response to homogenous or directional illumination, is reported and its relation to the run and tumble statistics of the cells is emphasized. In suspensions, there may exist a reciprocal interaction between the cell and the carrying fluid. The effects of shear flow on the growth, doubling per day, biomass production, pigments, and lipid production of are reported. Reciprocally, the effects of presence and its motility on the rheological properties of cell suspensions are addressed. This review only takes up the general grounds of cyanobacteria and does not get into the detailed biological aspects per se. Thus, it is substantially more comprehensive in that sense than other reviews that have been published in the last two decades. It is also written not only for the researchers in the field, but for those in physics and engineering, who may find it interesting, useful, and related to their own research.
PubMed: 35456747
DOI: 10.3390/microorganisms10040696 -
Journal of Plant Research May 2017Brown algae exhibit three patterns of sexual reproduction: isogamy, anisogamy, and oogamy. Unicellular swarmers including gametes and zoospores bear two heterogenous... (Review)
Review
Brown algae exhibit three patterns of sexual reproduction: isogamy, anisogamy, and oogamy. Unicellular swarmers including gametes and zoospores bear two heterogenous flagella, an anterior flagellum with mastigonemes (fine tripartite hairs) and a posterior one. In seawater, these flagellates usually receive physico-chemical signals for finding partners and good habitats. It is well known that brown algal swarmers change their swimming direction depending on blue light (phototaxis), and male gametes do so, based on the sex pheromones from female gametes (chemotaxis). In recent years, the comparative analysis of chemotaxis in isogamy, anisogamy, and oogamy has been conducted. In this paper, we focused on the phototaxis and chemotaxis of brown algal gametes comparing the current knowledge with our recent studies.
Topics: Chemotaxis; Fertilization; Flagella; Fluorescence; Light; Phaeophyceae; Pheromones; Phototaxis; Reproduction; Sperm Motility
PubMed: 28271338
DOI: 10.1007/s10265-017-0914-8 -
Integrative and Comparative Biology Nov 2016In many species of phytoplankton, simple photoreceptors monitor ambient lighting. Photoreceptors provide a number of selective advantages including the ability to assess...
In many species of phytoplankton, simple photoreceptors monitor ambient lighting. Photoreceptors provide a number of selective advantages including the ability to assess the time of day for circadian rhythms, seasonal changes, and the detection of excessive light intensities and harmful UV light. Photoreceptors also serve as depth gauges in the water column for behaviors such as diurnal vertical migration. Photoreceptors can be organized together with screening pigment into visible eyespots. In a wide variety of motile phytoplankton, including Chlamydomonas, Volvox, Euglena, and Kryptoperidinium, eyespots are light-sensitive organelles residing within the cell. Eyespots are composed of photoreceptor proteins and typically red to orange carotenoid screening pigments. This association of photosensory pigment with screening pigment allows for detection of light directionality, needed for light-guided behaviors such as positive and negative phototaxis. In Chlamydomonas, the eyespot is located in the chloroplast and Chlamydomonas expresses a number of photosensory pigments including the microbial channelrhodopsins (ChR1 and ChR2). Dinoflagellates are unicellular protists that are ecologically important constituents of the phytoplankton. They display a great deal of diversity in morphology, nutritional modes and symbioses, and can be photosynthetic or heterotrophic, feeding on smaller phytoplankton. Dinoflagellates, such as Kryptoperidinium foliaceum, have eyespots that are used for light-mediated tasks including phototaxis. Dinoflagellates belonging to the family Warnowiaceae have a more elaborate eye. Their eye-organelle, called an ocelloid, is a large, elaborate structure consisting of a focusing lens, highly ordered retinal membranes, and a shield of dark pigment. This complex eye-organelle is similar to multicellular camera eyes, such as our own. Unraveling the molecular makeup, structure and function of dinoflagellate eyes, as well as light-guided behaviors in phytoplankton can inform us about the selective forces that drove evolution in the important steps from light detection to vision. We show here that the evolution from simple photoreception to vision seems to have independently followed identical paths and principles in phytoplankton and animals, significantly strengthening our understanding of this important biological process.
Topics: Animals; Light; Locomotion; Phytoplankton; Ultraviolet Rays
PubMed: 27252218
DOI: 10.1093/icb/icw037 -
Philosophical Transactions of the Royal... Jan 2016Vision allows animals to detect spatial differences in environmental light levels. High-resolution image-forming eyes evolved from low-resolution eyes via increases in... (Review)
Review
Vision allows animals to detect spatial differences in environmental light levels. High-resolution image-forming eyes evolved from low-resolution eyes via increases in photoreceptor cell number, improvements in optics and changes in the neural circuits that process spatially resolved photoreceptor input. However, the evolutionary origins of the first low-resolution visual systems have been unclear. We propose that the lowest resolving (two-pixel) visual systems could initially have functioned in visual phototaxis. During visual phototaxis, such elementary visual systems compare light on either side of the body to regulate phototactic turns. Another, even simpler and non-visual strategy is characteristic of helical phototaxis, mediated by sensory-motor eyespots. The recent mapping of the complete neural circuitry (connectome) of an elementary visual system in the larva of the annelid Platynereis dumerilii sheds new light on the possible paths from non-visual to visual phototaxis and to image-forming vision. We outline an evolutionary scenario focusing on the neuronal circuitry to account for these transitions. We also present a comprehensive review of the structure of phototactic eyes in invertebrate larvae and assign them to the non-visual and visual categories. We propose that non-visual systems may have preceded visual phototactic systems in evolution that in turn may have repeatedly served as intermediates during the evolution of image-forming eyes.
Topics: Animals; Biological Evolution; Eye; Gene Expression Regulation; Opsins; Photoreceptor Cells
PubMed: 26598725
DOI: 10.1098/rstb.2015.0042