Sara Aspengren

Rapid color change in fish and amphibians – function, regulation, and emerging applications

Physiological color change is important for background matching, thermoregulation as well as signaling and is in vertebrates mediated by synchronous intracellular transport of pigmented organelles in chromatophores. We describe functions of and animal situations where color change occurs. A summary of endogenous and external factors that regulate this color change in fish and amphibians is provided, with special emphasis on extracellular stimuli. We describe not only color change in skin, but also highlight studies on color change that occurs using chromatophores in other areas such as iris and on the inside of the body. In addition, we discuss the growing field that applies melanophores and skin color in toxicology and as biosensors, and point out research areas with future potential.

Chapter 6 New Insights into Melanosome Transport in Vertebrate Pigment Cells

Pigment cells of lower vertebrates provide an excellent model to study organelle transport as they specialize in the translocation of pigment granules in response to defined chemical cues. This review will focus on the well-studied melanophore/melanocyte systems in fish, amphibians, and mammals. We will describe the roles of melanin, melanophores, and melanocytes in animals, current views on how the three motor proteins dynein, kinesin, and myosin-V are involved in melanosome transport along microtubules and actin filaments, and how signal transduction pathways regulate the activities of the motors to achieve aggregation and dispersion of melanosomes. We will also describe how melanosomes are transferred to surrounding skin cells in amphibians and mammals. Comparative studies have revealed that the ability of physiological color change is lost during evolution while the importance of morphological color change, mainly via transfer of pigment to surrounding skin cells, increases. In humans, pigment mainly has a role in protection against ultraviolet radiation, but also perhaps in the immune system.

Melanophores: A model system for neuronal transport and exocytosis?

Black pigment cells, melanophores, from lower vertebrates are specialized in bidirectional and coordinated translocation of pigment granules, melanosomes, in the cytoplasm. Melanophores develop from the neuronal crest and are most abundant in the dermal and epidermal layers of the skin, where the intracellular distribution of the pigment significantly influences the color of the animal. The transport of pigment is dependent on an intact cytoskeleton and motor proteins associated with cytoskeletal components. The easily cultured melanophores have proved to be excellent models for organelle transport because the intracellular movements of pigment can be visualized via light microscopy, and the granules move in response to defined chemical signals. The ease of achieving a combination of morphological and functional transport studies is the advantage of the melanophore system, and studies on pigment cells have revealed new components of the transport machinery, including molecular motors, their adapters, and transfer of vesicles to other cells. Many cellular components are transported with a combination of the actin‐ and microtubule‐based transport systems, and, since all eukaryotic organisms rely on functional intracellular transport and an intact cytoskeleton, studies on melanophores are important for many aspects of cell biology, including axonal transport. In this review, we present an overview of the research on the pigment transport system and the potential use of pigment cells as a model system.

Fish Chromatophores - From Molecular Motors to Animal Behavior

Chromatophores are pigment-bearing cells of lower vertebrates, including fish that cater for the ability of individual animals to shift body coloration and pattern. Color change provides dynamic camouflage and various kinds of communication. It is also a spectacular example of phenotypic plasticity, and of significant importance for adaptation and survival in novel environments. Through different cellular mechanisms, color change can occur within minutes or more slowly over weeks. Chromatophores have different pigment types and are located not only in the skin, but also in the eyes and internally. While morphological color change, including seasonal color change, has received a lot of interest from evolutionary biologists and behavioral ecologists, the more rapid physiological color change has been largely a research subject for cell physiologists. In this cross-disciplinary review, we have highlighted emerging trends in pigment cell research and identified unsolved problems for future research.

High-Throughput Transfection of Differentiated Primary Neurons from Rat Forebrain

Primary neurons in culture are considered to be a highly relevant model in the study of neuronal development and activity. They can be cultivated and differentiated in vitro but are difficult to transfect using conventional methods. To address this problem, a capillary electroporation system called Cellaxess Elektra was developed for efficient and reproducible transfection of primary cortical and hippocampal neurons without significant impact on cell morphology and viability. The cells are transfected in any stage of differentiation and development, directly in cell culture plates. Genetic material is delivered in situ to as many as 384 samples at a time, which enables both high-throughput and high-quality screening for hard-to-transfect primary cells, meaning that gene function can be studied on a genome-wide scale in cells previously inaccessible to genetic manipulation.

Effects of Hydroquinone on Cytoskeletal Organization and Intracellular Transport in Cultured Xenopus laevis Melanophores and Fibroblasts

Hydroquinone is used as a skin-lightening agent, it is also present in different chemical products and cigarette smoke. It is believed to inhibit melanin production in melanocytes by inhibiting the key enzyme tyrosinase. In the present study, we show that hydroquinone had severe effects on microtubules and actin filaments in cultured Xenopus laevis melanophores as studied by immunohistochemistry. It affected the intracellular transport of melanosomes, induced bundling of microtubules and disassembly of actin filaments at 10 and 50 μM, and at 100 μM proper adhesion to the substrate was lost. Effects occurred at lower concentrations than what previously has been stated to be cytotoxic, and the results show that tyrosinase is not the only cellular target. The cytoskeleton is of utmost importance for the function of all cells and across species. Our data has therefore to be considered in the discussions about the use of hydroquinone for bleaching of skin.