Biology subjects

Tardivo, P.

Publications and source records attributed to Tardivo, P..

3 recordsLinked to original sources

bioRxiv2026

Adult regenerative defects arise from discordant scaling of signal dependent growth and patterning

Orders of magnitude distinguish an organs size in adulthood from its size when patterning was established during embryonic development. The prospect of engineering adult organ regeneration raises the fundamental question of whether regenerative stem cell patterning should be elicited at embryonic or adult scale. Axolotls regenerate their limbs at all stages of post-embryonic life, encompassing an order of magnitude increase in animal size, but the mechanisms allowing this robust capacity remain unclear. Limb regeneration occurs by the formation of an embryonic-like progenitor zone, the blastema, whose dimensions increase with animal size, suggesting that at least some aspects of limb regeneration must scale. Here, by combining spatial transcriptomics, biophysical modelling, quantitative imaging, and functional perturbations, we found distinct scaling signatures among key signaling pathways, arguing against a body-size-dependent hormonal scaling mechanism. SHH signaling showed partial scaling that saturated in largest adult sizes, with a correspondingly early termination of blastema growth while Wnt9a-modulated digit patterning scaled at all animal sizes. As a result of this differential scaling, digit patterning wavelength was mismatched with respect to domain growth in the largest blastemas, preventing the addition of the last digit. In agreement with this model, regenerative failure can be rescued by timed supplementation of SHH. Our results show that coordinated scaling of morphogen signaling is a key requirement for adult organ regeneration.

systems biology↗

bioRxiv2025

Static morphogen scaling enables proportional growth in tissue growth model inspired by axolotl limb regeneration

Axolotls can regenerate lost limbs throughout life, while they continue to grow. This poses the question of how the size and pattern of a regenerating limb is matched to a widely varying animal size. Two interacting signaling molecules, SHH and FGF8, are produced at opposite sides of the regenerating limb and sustain tissue growth through a pair of oppositely-oriented signaling gradients. As the size of the regrowing tissue can vary more than three-fold depending on the size of the animal, it is unclear how the activities of these mutually dependent morphogens are maintained and subsequently terminated to determine appropriate growth. Scaling of limb regeneration suggests a size-dependent adaptation of morphogen gradient parameters. Inspired by this biological example, we theoretically investigate general mechanisms of morphogen-controlled growth arrest and proportional growth. In the proposed mechanism, tissue growth increases the spatial distance between the two morphogen gradients, which eventually arrests morphogen activity and growth. We put forward two distinct scaling scenarios of morphogen gradients: either dynamic scaling with blastema size, where morphogen gradient parameters change dynamically with the growing tissue, or static scaling with animal size, where morphogen gradient parameters stay constant during blastema growth and only depend on animal size. We show that static scaling ensures proportional growth, but dynamic scaling does not. We compare theory predictions to experimental quantification of SHH and FGF8 morphogen gradient parameters at different time-points of regeneration in different-sized animals, indicating static scaling for some morphogen parameters, which is sufficient to ensure proportional growth in our model.

biophysics↗

bioRxiv2022

Canonical Wnt Signaling and the Regulation of Divergent Mesenchymal Fgf8 expression in Axolotl Limb Development and Regeneration

The expression of Fibroblast growth factors (Fgf) ligands in a specialized epithelial compartment, the Apical Ectodermal Ridge (AER), is a conserved feature of limb development across vertebrate species. In vertebrates, Fgf 4, 8, 9, and 17 are all expressed in the AER. An exception to this paradigm is the salamander (axolotl) developing and regenerating limb, where key Fgf ligands are expressed in the mesenchyme. The mesenchymal expression of Amex.Fgf8 in axolotl has been suggested to be critical for regeneration. To date, there is little knowledge regarding what controls Amex.Fgf8 expression in the axolotl limb mesenchyme. A large body of mouse and chick studies have defined a set of transcription factors and canonical Wnt signaling as the main regulators of epidermal Fgf8 expression in these organisms. In this study, we address the hypothesis that alterations to one or more of these components during evolution has resulted in mesenchymal Amex.Fgf8 expression in the axolotl. To sensitively quantify gene expression with spatial precision, we combined optical clearing of whole-mount axolotl limb tissue with single molecule fluorescent in situ hybridization and a semi-automated quantification pipeline. Several candidate upstream components were found expressed in the axolotl ectoderm, indicating that they are not direct regulators of Amex.Fgf8 expression. We found that Amex.Wnt3a is expressed in axolotl limb epidermis, similarly to chicken and mouse. However, unlike in amniotes, Wnt target genes are activated preferentially in limb mesenchyme rather than in epidermis. Inhibition and activation of Wnt signaling results in downregulation and upregulation of mesenchymal Amex.Fgf8 expression respectively. These results implicate a shift in tissue responsiveness to canonical Wnt signaling from epidermis to mesenchyme as one step contributing to the unique mesenchymal Amex.Fgf8 expression seen in the axolotl.

developmental biology↗