Live Cell Imaging of Neural Stem Cells in the Drosophila Larval Brain

Long-term tracing of individual human neural cells using multiphoton microscopy and photoconvertible polymer capsules

The study of human neural cells, their behaviour and migration are important areas of research in the biomedical field, particularly for potential therapeutic applications. The safety of using neural cells in therapy is still a concern due to a lack of information on long-term changes that may occur. While current methods of cell tracing explore gene manipulations, we elaborate approaches to cell marking with no genetic interference. In this study, we present a novel method for labelling and tracking neural cells using cell-impregnatable photoconvertible polyelectrolyte microcapsules. These capsules demonstrated low cytotoxicity with no effect on the differentiation ability of the neural cells, maintained a high level of fluorescent signal and ability for tracing individual neural cells for over 7 days. The capsules modified with rhodamine- and fluorescein-based dyes were demonstrated to undergo photoconversion by both one- and two-photon lasers while being internalized by neural cells. The finding gives the possibility to select individual capsules inside multicellular structures like spheroids and tissues and alternate their fluorescent appearance. Thus, we can track individual cell paths in complex systems. This new method offers a promising alternative for studying neural cells' long-term behaviour and migration in complex systems such as three-dimensional cellular populations.

An Immobilization Technique for Long-Term Time-Lapse Imaging of Explanted Drosophila Tissues

Time-lapse imaging is an essential tool to study dynamic biological processes that cannot be discerned from fixed samples alone. However, imaging cell- and tissue-level processes in intact animals poses numerous challenges if the organism is opaque and/or motile. Explant cultures of intact tissues circumvent some of these challenges, but sample drift remains a considerable obstacle. We employed a simple yet effective technique to immobilize tissues in medium-bathed agarose. We applied this technique to study multiple Drosophila tissues from first-instar larvae to adult stages in various orientations and with no evidence of anisotropic pressure or stress damage. Using this method, we were able to image fine features for up to 18 h and make novel observations. Specifically, we report that fibers characteristic of quiescent neuroblasts are inherited by their basal daughters during reactivation; that the lamina in the developing visual system is assembled roughly 2-3 columns at a time; that lamina glia positions are dynamic during development; and that the nuclear envelopes of adult testis cyst stem cells do not break down completely during mitosis. In all, we demonstrate that our protocol is well-suited for tissue immobilization and long-term live imaging, enabling new insights into tissue and cell dynamics in Drosophila.