11.40 – 12.10
Stable Limb Morphogenesis Regardless of the Blastema Size in Limb Regeneration
Axolotls can regenerate their limbs throughout their life. Smaller animals having perfectly patterned limbs are about 3 cm and larger ones are about 30 cm. Regardless of the animal size, they exhibit perfect limb regeneration ability after limb amputation. It has been considered that limb regeneration is mostly a recapitulation of limb developmental processes. However, limb development always takes place in the identical size of the limb field. On the other hand, limb regeneration occurs in the various sizes of a limb. Those arose the question of how the developmental gene system is controlled in various sizes of a limb blastema. We focused on Shh and Fgf8 expression patterns in various sizes of axolotl limb blastemas. We investigated those expression patterns by in situ hybridization and found the expression domains of Shh and Fgf8 are varied in accordance with the blastema size. We found that the effects of the variation of gene expression patterns are buffered by the SHH diffusion range taking a relatively constant distance regardless of the blastema sizes. We concluded that the constant SHH diffusion contributes to creating consistent limb morphogenesis in various sizes of an axolotl limb. We also found that the constant SHH diffusion range creates an active proliferative zone (aPZ) within the constant range. Actually, the aPZ is under the influence of two mitogens, SHH and FGF8. We also found that the first phalangeal cartilage (digit II) emerged from the aPZ. Then, the aPZ is gradually shifted toward the posterior end, which contributes to posterior digit formation. This digital morphogenetic system also contributes to consistent limb morphogenesis. In the meeting, I would like to explain this complex and beautiful system to make consistent limb morphogenesis in various sizes of the field.
Tatiana Sandoval-Guźman (Online)
Biomechanics of skeletal formation in development and regeneration
Lizbeth A. Bolaños-Castro
Signaling Pathways Regulating Thymus Regeneration and Development in the Axolotl, Ambystoma Mexicanum
The thymus constitutes the main site for T cell development and maturation, and is thus central for the physiology of adaptive immunity. A hallmark of immune system aging is thymic involution, which has been observed across vertebrates and is regarded as a non-reversible process, highlighting the need for strategies promoting thymus regeneration. We have recently found that, exceptionally, the Mexican axolotl (A. mexicanum) is capable of de novo thymus regeneration. Here, we address the impact of diverse molecular pathways on thymus regeneration and development through pharmacological treatments, coupled with live imaging and whole-mount immunofluorescence. Through this approach, we find that the BMP and ERK pathways are necessary for thymus regeneration. Furthermore, by analyzing single cell RNAseq data from regenerating thymic nodules, we uncover a critical role for the Midkine pathway in thymus regeneration as well as development. This work broadens our understanding of thymus organogenesis and salamander immunity, laying the foundations for further comparative approaches across vertebrates.