@phdthesis{22804,
  abstract     = {Embryo cleavage — a series of rapid, reductive cell divisions — is the first morphogenetic movement following fertilisation. It lays the foundation for subsequent developmental events, including gastrulation, germ layer specification, organogenesis, and the establishment of the overall body plan. Two major modes of cleavage exist in the animal kingdom: holoblastic (complete) and meroblastic (incomplete) cleavage. Because holoblastic cleavage resembles canonical cytokinesis, its biochemical and mechanical basis has been extensively studied — an annular contractile ring forms at the equator and constricts in a purse-string-like manner, leading to the complete separation of two daughter cells. In contrast, although meroblastic cleavage occurs widely across the animal kingdom (e.g. in fish, reptiles, birds, and cephalopod molluscs), its mechanical basis remains largely unclear. During meroblastic cleavage, the cytokinetic furrow forms only at one pole and does not traverse the entire embryo, raising the question of how cytokinesis proceeds in the absence of a closed contractile ring. Moreover, the resulting daughter cells are not fully separated from the underlying yolk compartment, and how these blastomeres are subsequently cellularised remains unknown. This thesis takes the zebrafish as a model organism to address both questions. The first part characterises the biochemical and mechanical mechanisms underlying non-canonical meroblastic cleavage, revealing a two-phase process in which actomyosin cable contraction and cadherin-mediated membrane adhesion act sequentially to drive furrow ingression and invagination. The second part sheds light on the spatiotemporal dynamics by which individual blastomeres become cellularised, and uncovers a previously unrecognised contribution of central blastomeres to the yolk syncytial layer.},
  author       = {Tong, Xin},
  isbn         = {978-3-99078-080-0},
  issn         = {2663-337X},
  keywords     = {meroblastic cleavage, cytokinesis, active gel theory, embryogenesis, zebrafish, adhesion},
  pages        = {121},
  publisher    = {Institute of Science and Technology Austria},
  title        = {{Towards a deeper understanding of meroblastic cleavage}},
  doi          = {10.15479/AT-ISTA-22804},
  year         = {2026},
}

@misc{22777,
  author       = {Tong, Xin},
  publisher    = {Institute of Science and Technology Austria},
  title        = {{Towards a deeper understanding of meroblastic cleavage - supplementary movies}},
  doi          = {10.15479/AT-ISTA-22777},
  year         = {2026},
}

@unpublished{22807,
  abstract     = {Cleavage - the series of rapid cell divisions that follow fertilization - marks the onset of metazoan development and represents a deeply conserved evolutionary process. Across animals, two principal modes exist: complete (holoblastic) and incomplete (meroblastic) cleavage. While holoblastic cleavage resembles conventional cytokinesis both in vitro and in vivo, the mechanisms underlying meroblastic cleavage have remained poorly understood. Using zebrafish embryos as a model, we show that meroblastic cleavage proceeds through a distinct two-step mechanism. The process begins with the assembly and contraction of a large, arc-shaped actomyosin cable. However, this contractile event alone is insufficient to complete division. A second phase, driven by cadherin-mediated membrane adhesion, is required to invaginate the furrow ridge. Strikingly, this transition depends on mechanical uncoupling of the contractile cable from the surrounding cortex. We demonstrate that such uncoupling arises from an active nematic instability, which both enhances contractility along the cable and generates actin depletion zones that relieve lateral connections. Together, these findings reveal that meroblastic cleavage is governed not by a single actomyosin-based event but by a sequential interplay between cytoskeletal contraction and cadherin-dependent adhesion, highlighting a mechanism fundamentally distinct from canonical cytokinesis.},
  author       = {Tong, Xin and Li, Yuting I and Schelle, Joséphine and Hannezo, Edouard B and Heisenberg, Carl-Philipp J},
  booktitle    = {bioRxiv},
  title        = {{Non-canonical cytokinesis driven by mechanical uncoupling via nematic flows and adhesion-based invagination}},
  doi          = {10.1101/2025.10.15.682552},
  year         = {2025},
}

@article{19404,
  abstract     = {Cell migration is a fundamental process during embryonic development. Most studies in vivo have focused on the migration of cells using the extracellular matrix (ECM) as their substrate for migration. In contrast, much less is known about how cells migrate on other cells, as found in early embryos when the ECM has not yet formed. Here, we show that lateral mesendoderm (LME) cells in the early zebrafish gastrula use the ectoderm as their substrate for migration. We show that the lateral ectoderm is permissive for the animal-pole-directed migration of LME cells, while the ectoderm at the animal pole halts it. These differences in permissiveness depend on the lateral ectoderm being more cohesive than the animal ectoderm, a property controlled by bone morphogenetic protein (BMP) signaling within the ectoderm. Collectively, these findings identify ectoderm tissue cohesion as one critical factor in regulating LME migration during zebrafish gastrulation.},
  author       = {Tavano, Ste and Brückner, David and Tasciyan, Saren and Tong, Xin and Kardos, Roland and Schauer, Alexandra and Hauschild, Robert and Heisenberg, Carl-Philipp J},
  issn         = {2211-1247},
  journal      = {Cell Reports},
  number       = {3},
  publisher    = {Cell Press},
  title        = {{BMP-dependent patterning of ectoderm tissue material properties modulates lateral mesendoderm cell migration during early zebrafish gastrulation}},
  doi          = {10.1016/j.celrep.2025.115387},
  volume       = {44},
  year         = {2025},
}