Biology subjects

Dickmann, J. E. M.

Publications and source records attributed to Dickmann, J. E. M..

3 recordsLinked to original sources

bioRxiv2024

A comparative analysis of planarian regeneration specificity reveals tissue polarity contributions of the axial cWnt signalling gradient.

Planarians exhibit remarkable whole-body regeneration abilities. The formation of heads at forward-facing wounds and tails at rearward-facing wounds suggests an intrinsic tissue polarity guiding regeneration. While the underlying mechanisms remain unclear, reports of double-headed regenerates from increasingly narrow tissue fragments have long been hypothesised to reflect gradient-based polarity specification. Here, we systematically re-examine this hypothesis in the modern model species Schmidtea mediterranea and a representative of the genus likely used in the original studies, Girardia sinensis. While we never observed double-heads in S. mediterranea, G. sinensis readily regenerated double-heads in a manner dependent on piece length, anatomical position and body size. We found that the reduced regeneration robustness of G. sinensis was partially explained by wound site-symmetric expression of the head determinant notum, which is highly anterior-specific in S. mediterranea. Exploring what else might mediate head/tail regeneration specificity in G. sinensis, we examined the role of the conserved tail-to-head cWnt signalling gradient. By developing a time-resolved pharmacological approach to reduce the cWnt gradient slope without affecting wound-induced cWnt signalling dynamics, we observed an increased incidence of double-headed regenerates. In addition, the body size-dependence of double-head formation correlated with the decreasing steepness of the cWnt gradient due to scaling. Taken together, our results indicate that the slope of the cWnt gradient may contribute to planarian head/tail regeneration specificity. Furthermore, they suggest that planarian tissue polarity is composed of multiple parallely-acting polarity cues, the differential reliance on which contributes to the observed interspecies variation in regeneration specificity.

developmental biology↗

bioRxiv2024

Dynamic cortical behavior of plant protoplasts reveals unexpected similarities between plant and animal cells

In contrast to animal cells with their contractile cortical cytoskeleton, plant cells are encased in walls and are usually thought to behave like stiff, pressurized vessels. When digesting the cell wall, plant protoplasts form spherical shapes, further consolidating this model. Here we challenge this apparent opposition between animal and plant cells. We show that plant protoplasts can form protrusions. More precisely, using plasma membrane markers, we reveal that 27 {+/-} 1% of the protoplasts show dot-like protrusions and 16 {+/-} 7% of protoplasts show long (typically 1-20 m, up to 200 m) protrusions that we name "filopods". We demonstrate that this behavior is independent of the plant species, the membrane marker or the osmolyte. Protrusions can host large and long structures, such as microtubule bundles, which in turn can impact the mechanical behavior of the protrusions. We find that filopods can form de novo when increasing osmolarity, that they most likely move passively, and that they can attach to artificial surfaces. Altogether, these observations show that forming and retaining protrusions is not exclusive to animal cells. This calls for revisiting the dynamics and probing ability of the plant cell cortex in different osmotic and mechanical environments.

plant biology↗

bioRxiv2022

Long-range morphogen gradient formation by cell-to-cell signal propagation

Morphogen gradients are a central concept in developmental biology. Their formation often involves the secretion of morphogens from a local source, that spread by diffusion in the cell field, where molecules eventually get degraded. This implies limits to both the time and length scales over which morphogen gradients can form which are set by diffusion coefficients and degradation rates. Towards the goal of identifying plausible mechanisms capable of extending the gradient range, we here use theory to explore properties of a cell-to-cell signaling relay. Inspired by the millimeter-scale Wnt-expression and signaling gradients in flatworms, we consider morphogen-mediated morphogen production in the cell field. We show that such a relay can generate stable morphogen and signaling gradients that emanate from a source of morphogen at a boundary. This gradient formation can be related to an effective diffusion and an effective degradation that result from morphogen production due to signaling relay. If the secretion of morphogen produced in response to the relay is polarized, it further gives rise to an effective drift. We find that signaling relay can generate long-ranged gradients in relevant times without relying on extreme choices of diffusion coefficients or degradation rates, thus exceeding the limits set by physiological diffusion coefficients and degradation rates. A signaling relay is hence an attractive principle to conceptualize long-ranged gradient formation by slowly diffusing morphogens that are relevant for patterning in adult contexts such as regeneration and tissue turn-over.

biophysics↗