Cell delamination is a conserved morphogenetic process important for the generation of cell diversity and maintenance of tissue homeostasis. Here, we used Drosophila embryonic neuroblasts as a model to study the apical constriction process during cell delamination. We observe dynamic myosin signals both around the cell adherens junctions and underneath the cell apical surface in the neuroectoderm. On the cell apical cortex, the nonjunctional myosin forms flows and pulses, which are termed medial myosin pulses. Quantitative differences in medial myosin pulse intensity and frequency are crucial to distinguish delaminating neuroblasts from their neighbors. Inhibition of medial myosin pulses blocks delamination. The fate of a neuroblast is set apart from that of its neighbors by Notch signaling-mediated lateral inhibition. When we inhibit Notch signaling activity in the embryo, we observe that small clusters of cells undergo apical constriction and display an abnormal apical myosin pattern. Together, these results demonstrate that a contractile actomyosin network across the apical cell surface is organized to drive apical constriction in delaminating neuroblasts.

We experimentally demonstrated Bessel-like beams utilizing digital micromirror device (DMD). DMD with images imitating the equivalent axicon can shape the collimated Gaussian beam into Bessel beam. We reconstructed the 3D spatial field of the generated beam through a stack of measured cross-sectional images. The output beams have the profile of Bessel function after intensity modulation, and the beams extend at least 50 mm while the lateral dimension of the spot remains nearly invariant. Furthermore, the self-healing property has also been investigated, and all the experimental results agree well with simulated results numerically calculated through beam propagation method. Our observations demonstrate that the DMD offers a simple and efficient method to generate Bessel beams with distinct nondiffracting and self-reconstruction behaviors. The generated Bessel beams will potentially expand the applications to the optical manipulation and high-resolution fluorescence imaging owing to the unique nondiffracting property.

In this work, three kinds of vesicles are fabricated by the self-assembly of amphiphilic block copolymers (BCPs), in which the hydrophobic chains are side chain azobenzene polymers with spacers of 0, 2 and 6 methylene units, respectively. It has been found that vesicles formed by BCPs with a spacer of 0 methylene units have no photo-responsive behavior and vesicles with a spacer of 6 have a photoinduced swelling behavior under the irradiation of light at 365 nm. Unexpectedly, the vesicle formed by BCPs with a spacer of 2 shows a photo-induced reversible uniform to Janus shape change under the same irradiation. This reversible process means that a bistable shape change of the vesicle can be controlled by the switching of UV light. A UV-visible absorption spectrum and a laser-trapped Raman spectrum (LTRS) are used to investigate differences in the morphology and photo-induced behavior of these vesicles. Results have confirmed that the photo-induced Janus shape of vesicles formed by BCPs with a spacer of 2 is a metastable shape, different from the stable Janus shape of vesicles formed by BCPs with a spacer of 0. This is also testified by a two-photon confocal laser scanning microscope (CLSM). From the results it is realized that the spacer length in the hydrophobic chains of BCPs can affect the photo-induced behavior of vesicles formed by BCPs, which will be a key point in designing functional vesicles with special morphologies.

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