Optogenetic manipulation of cellular communication in axolotls

Cells communicate through long cellular protrusions such as filopodia and neurites. However current approaches to study these contact-based cellular communication are largely limited to actin-depolymerizing drugs or genetic knockout of key actin modifiers which can cause severe cellular stress or semi-lethality in organisms. Here we present a versatile optogenetic toolbox of artificial myosin motors that can move bidirectionally within long cellular extensions and allow for the selective transport of GFP-tagged cargo using light. Importantly, we discover that these long filopodial extensions are also gradually developed during axolotl limb regeneration, where we applied our toolbox to manipulate the composition and dynamics of these cellular extensions.

Actin bundles play a different role in shaping scales compared to bristles in the mosquito Aedes aegypti

Insect epithelial cells contain cellular extensions such as bristles, hairs, and scales. These cellular extensions are homologous structures that differ in morphology and function. They contain actin bundles that dictate their cellular morphology. While the organization, function, and identity of the major actin-bundling proteins in bristles and hairs are known, this information on scales is unknown. In this study, we characterized the development of scales and the role of actin bundles in the mosquito, Aedes aegypti. We show that scales undergo drastic morphological changes during development, from a cylindrical to flat shape with longer membrane invagination. Scale actin-bundle distribution changes from the symmetrical organization of actin bundles located throughout the bristle membrane to an asymmetrical organization. By chemically inhibiting actin polymerization and by knocking out the forked gene in the mosquito (Ae-Forked; a known actin-bundling protein) by CRISPR-Cas9 gene editing, we showed that actin bundles are required for shaping bristle, hair, and scale morphology. We demonstrated that actin bundles and Ae-Forked are required for bristle elongation, but not for that of scales. In scales, actin bundles are required for width formation. In summary, our results reveal, for the first time, the developmental process of mosquito scale formation and also the role of actin bundles and actin-bundle proteins in scale morphogenesis. Moreover, our results reveal that although scale and bristle are thought to be homologous structures, actin bundles have a differential requirement in shaping mosquito scales compared to bristles.

Actin bundles play different role in shaping scale as compare to bristle in mosquito Aedes aegypti

Insect epithelial cells contain cellular extensions such as bristles, hairs and scales. It has been suggested that these cellular extensions are homologous structures that differ in morphology and function. These cellular extensions contain actin bundles that dictate their cellular morphology; bristle and hair are cylindrical in shape, while scales are wider and flattened. While the organization, function and identity of the major actin bundling protein in bristles and hairs is known, this information in scales is unknown. In this study, we characterized the development of scales and the role of actin bundles in the mosquito, Aedes aegypti. We show that scales undergo drastic morphological changes during development, from cylindrical shape to flat shape with longer membrane invagination. Scale actin bundle distribution changes during development, from symmetrical organization of actin bundles located throughout the bristle membrane, to asymmetrical organization of the actin bundles. By chemically inhibiting actin polymerization and by knocking-out the forked gene in the mosquito (Ae-Forked; a known actin bundling protein), by CRISPR-Cas9 gene editing, we showed that actin bundles are required for shaping bristle, hair and scale morphology. We demonstrated that actin bundles and Ae-Forked are required for bristle elongation, but not that of scales. In scales, actin bundles are required for width formation. Our results reveal a differential requirement of actin bundles in shaping mosquito scales compared to bristles.

A lumenal interrupted helix in human sperm tail microtubules

Eukaryotic flagella are complex cellular extensions involved in many human diseases gathered under the term ciliopathies. Currently, detailed insights on flagellar structure come from studies on protozoa. Here, cryo-electron tomography (cryo-ET) of intact human spermatozoon tails showed a variable number of microtubules in the singlet region. Inside their lumen, a novel left-handed interrupted helix which extends several micrometers at their plus ends was discovered. This structure was named Tail Axoneme Intra-Lumenal Spiral (TAILS) and binds directly to 11 protofilaments on the internal microtubule wall, coaxial with the surrounding microtubule lattice. It leaves a gap over the microtubule seam, which was directly visualized in both singlet and doublet microtubules. We suggest that TAILS may stabilize microtubules, enable rapid swimming or play a role in controlling the swimming direction of spermatozoa.

The central nervous system

The nervous system is an integrating system which acts rapidly by transmitting signals as electrical impulses over often considerable distances to coordinate bodily activities. The brain and spinal cord make up the central nervous system (CNS); incoming information travels in ascending (sensory) tracts that link the spinal cord to the brain and outgoing information passes down descending (motor) tracts linking the brain to the spinal cord. The CNS integrates responses to incoming information and sends the information to effector tissues (usually striated or smooth muscles or glands). Incoming and outgoing information is carried to and from the periphery to the CNS via 12 pairs of cranial nerves connected to the brain and 31 pairs of spinal nerves connected to the spinal cord; they constitute the peripheral nervous system (PNS). Sensory (afferent) information from the external environment is obtained through the organs of special sense in the eyes, ears, nose and tongue, and skin and mucosa lining bodily cavities: we are aware of these stimuli. Information from internal sources is equally important and vital for maintaining homeostasis, but we are usually Neurons are the basic cellular units of the nervous system. As the principal function of the nervous system is conduction of electrical signals over considerable distances, neurons are highly specialized for this f unction. Neurons have: • A specific shape with long cellular extensions; • Highly specialized membranes to control ionic movements to allow electrical activity to spread along the cellular extensions; • A very specialized internal transport system to distribute cellular metabolites along the processes. The general shape of neurons is shown in Figure 3.1. Note first of all, the relatively large cell body near the top of the picture; this contains the nucleus and the intracellular organelles necessary for synthetic functions so is similar to any other cell. What make neurons special are the long processes that emanate from the cell body. Dendrites are short multiple processes that branch extensively from and transmit impulses towards the cell body. Compare the dendrites in Figure 3.1 with the other process, the axon, which transmits impulses away from the cell body.