Biology subjects

Mercadal, J.

Publications and source records attributed to Mercadal, J..

5 recordsLinked to original sources

bioRxiv2025

Lateral inhibition governs ancestral cellular patterning in fossil and extant liverworts

The incompleteness of the fossil record and the absence of genetic information limit our ability to understand ancient developmental processes and reconstruct their evolution. Here, we use comparative and mathematical analyses to uncover an evolutionarily conserved patterning mechanism underlying liverwort oil body cell specification. We demonstrate that patterns of oil body cell homologs in fossils of the oldest known liverwort (Metzgeriothallus sharonae) exhibit the spatial organization characteristic of lateral inhibition. A mechanism with local activation and lateral inhibition not only reproduces the patterns observed in fossils, but also oil body cell patterns in the extant liverworts Treubia lacunosa, Apotreubia nana, and Marchantia polymorpha. Our results point to an ancestral patterning mechanism that has been modulated by lineage-specific selective pressures over evolutionary time.

developmental biology↗

bioRxiv2025

Homology of the dark cells of Paleozoic liverworts with the specialized oil body cells of modern liverworts (Marchantiophyta)

O_LIOil bodies are a synapomorphy of liverworts (Marchantiophyta), a major group of land plants with a sparse fossil record. Paleozoic liverworts sometimes possess dark cells that appear similar in distribution to liverwort oil body cells. The Middle Devonian Metzgeriothallus sharonae provides an opportunity for comparison with modern liverworts. C_LIO_LIShale samples were collected and the carbonaceous fossils isolated by acid maceration. Museum shale specimens of Pallaviciniites devonicus were also obtained and processed. The relative location, composition, frequency and spatial distribution of the fossil dark cells was compared to that of oil cells in extant taxa. C_LIO_LIChemical characterization of the fossil dark cells is consistent with cells that contained lipids, the main component of oil bodies. Quantitative analyses revealed that the frequency and spatial distribution of dark cells are comparable to oil body cells. The dark cells of M. sharonae show clumping near the thallus edge, suggesting an anti-herbivore function. C_LIO_LIThese results support the hypothesis that the dark cells of Paleozoic liverworts and the oil body cells of extant lineages are homologous structures with a shared developmental origin, providing a new character that can be used to assign fossils and that sheds light on the evolution and function of liverwort oil bodies. C_LI

paleontology↗

bioRxiv2023

A diffusion-driven switch specifies rhizoid precursor cells in Marchantia polymorpha

The specification of rhizoid precursor cells in the epidermis of Marchantia polymorpha gemmae has been shown to involve lateral inhibition mediated by the microRNA FRH1, which represses its activator RSL1, a rhizoidspecific transcription factor. However, how inhibition is conferred to adjacent cells and which is the mechanism underlying the emergence of rhizoid precursors remain unknown. In this paper, we use mathematical and computational modeling to show that the previously reported rhizoid patterns in WT, gain-of-function and lossof-function mutants of FRH1 and RSL1 are consistent with lateral inhibition mediated by a mobile FRH1. Our modeling results suggest that cells in Marchantia wildtype gemmae reside close to a critical state, where diffusion of FRH1 drives a switch of RSL1 expression that specifies rhizoid precursors. This process involves an initially random trigger and subsequent lateral inhibition, leading to cellular patterns consisting of small and filamentous clusters of rhizoid precursors. We confirm these predictions with new data on WT rhizoid distributions. Our findings highlight a novel mechanism of cellular pattern formation, opening new research directions for understanding cellular differentiation and tissue morphogenesis, with potential implications for a broad range of biological systems.

systems biology↗

bioRxiv2021

Self-confined expression in the Arabidopsis root stem cell niche

Stem cell niches are local microenvironments that preserve their unique identity while communicating with adjacent tissues. In the primary root of Arabidopsis thaliana, the stem cell niche comprises the expression of two transcription factors, BRAVO and WOX5, among others. Intriguingly, these proteins confine their own gene expression to the niche, as evidenced in each mutant background. Here we propose through mathematical modeling that BRAVO confines its own expression domain to the stem cell niche by attenuating its WOX5-dependent diffusible activator. This negative feedback drives WOX5 action to be spatially restricted as well. The results show that WOX5 diffusion and sequestration by binding to BRAVO is sufficient to drive realistic confined BRAVO expression at the stem cell niche. We propose that attenuation of a diffusible activator can be a general mechanism to confine genetic activity to a small region while at the same time maintain signaling within it and with the surrounding cells.

systems biology↗

bioRxiv2020

Precise transcriptional control of cellular quiescence by BRAVO/WOX5 complex in Arabidopsis roots

Root growth and development are essential features for plant survival and the preservation of terrestrial ecosystems. In the Arabidopsis primary root apex, stem-cell specific transcription factors BRAVO and WOX5 co-localize at the Quiescent Center (QC) cells, where they repress cell division so that these cells can act as a reservoir to replenish surrounding stem cells, yet their molecular connection remains unknown. Here, by using empirical evidence and mathematical modeling, we establish the precise regulatory and molecular interactions between BRAVO and WOX5. We found that BRAVO and WOX5 regulate each other besides forming a transcription factor complex in the QC necessary to preserve overall root growth and architecture. Our results unveil the importance of transcriptional regulatory circuits at the quiescent and stem cells to the control of organ initiation and growth of plant tissues.

plant biology↗