Of mice and plants: Comparative developmental systems biology

Biomimetic structural design in 3D-printed scaffolds for bone tissue engineering

The rising prevalence of bone diseases in an aging population underscores the urgent need for innovative and clinically translatable solutions in bone tissue engineering. While significant progress has been made in refining the chemical properties of biomaterials, the structural design of scaffolds-a critical determinant of repair success-remains comparatively underexplored. Structural parameters such as porosity, pore size, and interconnectivity are not only essential for achieving mechanical stability but also pivotal in regulating biological processes, including vascularization, osteogenesis, and immune modulation. This review systematically categorizes scaffold architectures documented in the literature and highlights how these design parameters can be optimized to enhance bone regeneration. Advanced fabrication technologies, particularly 3D printing, are emphasized for their transformative potential in creating precise, biomimetic scaffolds that align with the complex functional demands of native bone. Furthermore, this work synthesizes diverse findings to provide a comprehensive framework for designing next-generation scaffolds. By bridging the gap between structural innovation and clinical application, this review delivers actionable strategies and a strategic roadmap for advancing the field toward improved clinical outcomes and transformative breakthroughs in regenerative medicine.

A new motile animal with implications for the evolution of axial polarity from the Ediacaran of South Australia

Fossils of the Ediacara Biota preserve the oldest evidence for complex, macroscopic animals. Most are difficult to constrain phylogenetically, however, the presence of rare, derived groups suggests that many more fossils from this period represent extant groups than are currently appreciated. One approach to recognize such early animals is to instead focus on characteristics widespread in animals today, for example multicellularity, motility, and axial polarity. Here, we describe a new taxon, Quaestio simpsonorum gen. et sp. nov. from the Ediacaran of South Australia. Quaestio is reconstructed with a thin external membrane connecting more resilient tissues with anterior-posterior polarity, left-right asymmetry and tentative evidence for dorsoventral differentiation. Associated trace fossils indicate an epibenthic and motile lifestyle. Our results suggest that Quaestio was a motile eumetazoan with a body plan not previously recognized in the Ediacaran, including definitive evidence of chirality. This organization, combined with previous evidence for axial patterning in a variety of other Ediacara taxa, demonstrates that metazoan body plans were well established in the Precambrian.

Exploring the patterns of evolution: Core thoughts and focus on the saltational model

The Modern Synthesis, a pillar in biological thought, united Darwin's species origin concepts with Mendel's laws of character heredity, providing a comprehensive understanding of evolution within species. Highlighting phenotypic variation and natural selection, it elucidated the environment's role as a selective force, shaping populations over time. This framework integrated additional mechanisms, including genetic drift, random mutations, and gene flow, predicting their cumulative effects on microevolution and the emergence of new species. Beyond the Modern Synthesis, the Extended Evolutionary Synthesis expands perspectives by recognizing the role of developmental plasticity, non-genetic inheritance, and epigenetics. We suggest that these aspects coexist in the plant evolutionary process; in this context, we focus on the saltational model, emphasizing how saltation events, such as dichotomous saltation, chromosomal mutations, epigenetic phenomena, and polyploidy, contribute to rapid evolutionary changes. The saltational model proposes that certain evolutionary changes, such as the rise of new species, may result suddenly from single macromutations rather than from gradual changes in DNA sequences and allele frequencies within a species over time. These events, observed in domesticated and wild higher plants, provide well-defined mechanistic bases, revealing their profound impact on plant diversity and rapid evolutionary events. Notably, next-generation sequencing exposes the likely crucial role of allopolyploidy and autopolyploidy (saltational events) in generating new plant species, each characterized by distinct chromosomal complements. In conclusion, through this review, we offer a thorough exploration of the ongoing dissertation on the saltational model, elucidating its implications for our understanding of plant evolutionary processes and paving the way for continued research in this intriguing field.

Crucial Development: Criticality Is Important to Cell-to-Cell Communication and Information Transfer in Living Systems

In the fourth paper of this Special Issue, we bridge the theoretical debate on the role of memory and criticality discussed in the three earlier manuscripts, with a review of key concepts in biology and focus on cell-to-cell communication in organismal development. While all living organisms are dynamic complex networks of organization and disorder, most studies in biology have used energy and biochemical exchange to explain cell differentiation without considering the importance of information (entropy) transfer. While all complex networks are mixtures of patterns of complexity (non-crucial and crucial events), it is the crucial events that determine the efficiency of information transfer, especially during key transitions, such as in embryogenesis. With increasing multicellularity, emergent relationships from cell-to-cell communication create reaction-diffusion exchanges of different concentrations of biochemicals or morphogenetic gradients resulting in differential gene expression. We suggest that in conjunction with morphogenetic gradients, there exist gradients of information transfer creating cybernetic loops of stability and disorder, setting the stage for adaptive capability. We specifically reference results from the second paper in this Special Issue, which correlated biophotons with lentil seed germination to show that phase transitions accompany changes in complexity patterns during development. Criticality, therefore, appears to be an important factor in the transmission, transfer and coding of information for complex adaptive system development.

Developmental processes in Ediacara macrofossils

The Ediacara Biota preserves the oldest fossil evidence of abundant, complex metazoans. Despite their significance, assigning individual taxa to specific phylogenetic groups has proved problematic. To better understand these forms, we identify developmentally controlled characters in representative taxa from the Ediacaran White Sea assemblage and compare them with the regulatory tools underlying similar traits in modern organisms. This analysis demonstrates that the genetic pathways for multicellularity, axial polarity, musculature, and a nervous system were likely present in some of these early animals. Equally meaningful is the absence of evidence for major differentiation of macroscopic body units, including distinct organs, localized sensory machinery or appendages. Together these traits help to better constrain the phylogenetic position of several key Ediacara taxa and inform our views of early metazoan evolution. An apparent lack of heads with concentrated sensory machinery or ventral nerve cords in such taxa supports the hypothesis that these evolved independently in disparate bilaterian clades.

Fgf4 maintains Hes7 levels critical for normal somite segmentation clock function

During vertebrate development, the presomitic mesoderm (PSM) periodically segments into somites, which will form the segmented vertebral column and associated muscle, connective tissue, and dermis. The periodicity of somitogenesis is regulated by a segmentation clock of oscillating Notch activity. Here, we examined mouse mutants lacking only Fgf4 or Fgf8, which we previously demonstrated act redundantly to prevent PSM differentiation. Fgf8 is not required for somitogenesis, but Fgf4 mutants display a range of vertebral defects. We analyzed Fgf4 mutants by quantifying mRNAs fluorescently labeled by hybridization chain reaction within Imaris-based volumetric tissue subsets. These data indicate that FGF4 maintains Hes7 levels and normal oscillatory patterns. To support our hypothesis that FGF4 regulates somitogenesis through Hes7, we demonstrate genetic synergy between Hes7 and Fgf4, but not with Fgf8. Our data indicate that Fgf4 is potentially important in a spectrum of human Segmentation Defects of the Vertebrae caused by defective Notch oscillations.