Live imaging of development in fish embryos

Possibilities and limitations of three-dimensional reconstruction and simulation techniques to identify patterns, rhythms and functions of apoptosis in the early developing neural tube

The now classical idea that programmed cell death (apoptosis) contributes to a plethora of developmental processes still has lost nothing of its impact. It is, therefore, important to establish effective three-dimensional (3D) reconstruction as well as simulation techniques to decipher the exact patterns and functions of such apoptotic events. The present study focuses on the question whether and how apoptosis promotes neurulation-associated processes in the spinal cord of Tupaia belangeri (Tupaiidae, Scandentia, Mammalia). Our 3D reconstructions demonstrate that at least two craniocaudal waves of apoptosis consecutively pass through the dorsal spinal cord. The first wave appears to be involved in neural fold fusion and/or in selection processes among premigratory neural crest cells. The second one seems to assist in establishing the dorsal signaling center known as the roof plate. In the hindbrain, in contrast, apoptosis among premigratory neural crest cells progresses craniocaudally but discontinuously, in a segment-specific manner. Unlike apoptosis in the spinal cord, these segment-specific apoptotic events, however, precede later ones that seemingly support neural fold fusion and/or postfusion remodeling. Arguing with Whitehead that biological patterns and rhythms differ in that biological rhythms depend "upon the differences involved in each exhibition of the pattern" (Whitehead in An enquiry concerning the principles of natural knowledge. Cambridge University Press, London, 1919, p. 198) we show that 3D reconstruction and simulation techniques can contribute to distinguish between (static) patterns and (dynamic) rhythms of apoptosis. By deciphering novel patterns and rhythms of developmental apoptosis, our reconstructions help to reconcile seemingly inconsistent earlier findings in chick and mouse embryos, and to create rules for computer simulations.

All-in-one 3D printed microscopy chamber for multidimensional imaging, the UniverSlide

While live 3D high resolution microscopy techniques are developing rapidly, their use for biological applications is partially hampered by practical difficulties such as the lack of a versatile sample chamber. Here, we propose the design of a multi-usage observation chamber adapted for live 3D bio-imaging. We show the usefulness and practicality of this chamber, which we named the UniverSlide, for live imaging of two case examples, namely multicellular systems encapsulated in sub-millimeter hydrogel shells and zebrafish larvae. We also demonstrate its versatility and compatibility with all microscopy devices by using upright or inverted microscope configurations after loading the UniverSlide with fixed or living samples. Further, the device is applicable for medium/high throughput screening and automatized multi-position image acquisition, providing a constraint-free but stable and parallelized immobilization of the samples. The frame of the UniverSlide is fabricated using a stereolithography 3D printer, has the size of a microscopy slide, is autoclavable and sealed with a removable lid, which makes it suitable for use in a controlled culture environment. We describe in details how to build this chamber and we provide all the files necessary to print the different pieces in the lab.

Enteric nervous system development in avian and zebrafish models

Our current understanding of the developmental biology of the enteric nervous system (ENS) and the genesis of ENS diseases is founded almost entirely on studies using model systems. Although genetic studies in the mouse have been at the forefront of this field over the last 20 years or so, historically it was the easy accessibility of the chick embryo for experimental manipulations that allowed the first descriptions of the neural crest origins of the ENS in the 1950s. More recently, studies in the chick and other non-mammalian model systems, notably zebrafish, have continued to advance our understanding of the basic biology of ENS development, with each animal model providing unique experimental advantages. Here we review the basic biology of ENS development in chick and zebrafish, highlighting conserved and unique features, and emphasising novel contributions to our general understanding of ENS development due to technical or biological features.

Building a plant: cell fate specification in the early Arabidopsis embryo

Embryogenesis is the beginning of plant development, yet the cell fate decisions and patterning steps that occur during this time are reiterated during development to build the post-embryonic architecture. In Arabidopsis, embryogenesis follows a simple and predictable pattern, making it an ideal model with which to understand how cellular and tissue developmental processes are controlled. Here, we review the early stages of Arabidopsis embryogenesis, focusing on the globular stage, during which time stem cells are first specified and all major tissues obtain their identities. We discuss four different aspects of development: the formation of outer versus inner layers; the specification of vascular and ground tissues; the determination of shoot and root domains; and the establishment of the first stem cells.

Development of a multiplexed microfluidic platform for the automated cultivation of embryonic stem cells

We present a multiplexed platform for a microfabricated stem cell culture device. The modular platform contains all the components to control stem cell culture conditions in an automated fashion. It does not require an incubator during perfusion culture and can be mounted on the stage of an inverted fluorescence microscope for high-frequency imaging of stem cell cultures. A pressure-driven pump provides control over the medium flow rate and offers switching of the flow rates. Flow rates of the pump are characterized for different pressure settings, and a linear correlation between the applied pressure and the flow rate in the cell culture devices is shown. In addition, the pump operates with two culture medium reservoirs, thus enabling the switching of the culture medium on-the-fly during a cell culture experiment. Also, with our platform, the culture medium reservoirs are cooled to prevent medium degradation during long-term experiments. Media temperature is then adjusted to a higher controlled temperature before entering the microfabricated cell culture device. Furthermore, the temperature is regulated in the microfabricated culture devices themselves. Preliminary culture experiments are demonstrated using mouse embryonic stem cells.

Noninvasive imaging of ethanol-induced developmental defects in zebrafish embryos using optical coherence tomography

In this article, we report the use of optical coherence tomography for noninvasive cross-sectional real-time imaging of ethanol-induced developmental defects in zebrafish embryos larvae. For ethanol concentration of over 300 mM, developmental defects of eye (shrinkage and retinal abnormalities), malformation of the notochord and ataxia arising due to the toxic effects of ethanol were observed in OCT images from 3 days post fertilization onwards. The results suggest that OCT could be a valuable tool for noninvasive assessment of birth defects in small animal systems.

A polarised population of dynamic microtubules mediates homeostatic length control in animal cells

An analysis of cells grown on micro-patterned lines, and of cells during zebrafish development, identifies a population of microtubules that align along the long axis of cells to mediate homeostatic length control.

Because physical form and function are intimately linked, mechanisms that maintain cell shape and size within strict limits are likely to be important for a wide variety of biological processes. However, while intrinsic controls have been found to contribute to the relatively well-defined shape of bacteria and yeast cells, the extent to which individual cells from a multicellular animal control their plastic form remains unclear. Here, using micropatterned lines to limit cell extension to one dimension, we show that cells spread to a characteristic steady-state length that is independent of cell size, pattern width, and cortical actin. Instead, homeostatic length control on lines depends on a population of dynamic microtubules that lead during cell extension, and that are aligned along the long cell axis as the result of interactions of microtubule plus ends with the lateral cell cortex. Similarly, during the development of the zebrafish neural tube, elongated neuroepithelial cells maintain a relatively well-defined length that is independent of cell size but dependent upon oriented microtubules. A simple, quantitative model of cellular extension driven by microtubules recapitulates cell elongation on lines, the steady-state distribution of microtubules, and cell length homeostasis, and predicts the effects of microtubule inhibitors on cell length. Together this experimental and theoretical analysis suggests that microtubule dynamics impose unexpected limits on cell geometry that enable cells to regulate their length. Since cells are the building blocks and architects of tissue morphogenesis, such intrinsically defined limits may be important for development and homeostasis in multicellular organisms.

Because many physical processes change with scale, size control is a fundamental problem for living systems. While in some instances the size of a structure is directly determined by the dimensions of its individual constituents, many biological structures are dynamic, self-organising assemblies of relatively small component parts. How such assemblies are maintained within defined size limits remains poorly understood. Here, by confining cells to spread on lines, we show that animal cells reach a defined length that is independent of their volume and width. In searching for a “ruler” that might determine this axial limit to cell spreading, we identified a population of dynamic microtubule polymers that become oriented along the long axis of cells. This growing population of oriented microtubules drives extension of the spreading cell margin while, conversely, interactions with the cell margin promote microtubule depolymerisation, leading to cell shortening. Using a mathematical model we show that this coupling of dynamic microtubule polymerisation and depolymerisation with directed cell elongation is sufficient to explain the limit to cell spreading and cell length homeostasis. Because microtubules appear to regulate cell length in a similar way in the developing zebrafish neural tube, we suggest that this microtubule-dependent mechanism is likely to be of widespread importance for the regulation of cell and tissue geometry.