A transcription factor toggle switch determines differentiated epidermal cell identities in Hydra.

In Hydra, a simple cnidarian model, epithelio-muscular cells shape and maintain body architecture through continuous renewal. Undifferentiated cells from the mid-body region migrate passively toward the extremities, replacing shed cells and acquiring region-specific identities. This ongoing turnover, together with Hydra's stable axial organization, provides a powerful model to study how cell type specification is integrated with body patterning.

Mechanochemical patterning localizes the organizer of a luminal epithelium.

The spontaneous emergence of tissue patterns is often attributed to biochemical reaction-diffusion systems. In tissue regeneration, the formation of a Wnt signaling center exemplifies this process. However, a strictly biochemical mechanism for self-organization in remains elusive.

Unidirectional and phase-gated signaling synchronizes murine presomitic mesoderm cells.

Oscillator systems achieve synchronization when oscillators are coupled. The presomitic mesoderm is a system of cellular oscillators, where coordinated genetic activity is necessary for proper periodic generation of somites. While Notch signaling is required for the synchronization of these cells, it is unclear what information the cells exchange and how they react to this information to align their oscillatory pace with that of their neighbors.

Studying Mechanical Oscillations During Whole-Body Regeneration in Hydra.

Cells of the freshwater cnidarian Hydra possess an exceptional regeneration ability. In small groups of these cells, organizer centers emerge spontaneously and instruct the patterning of the surrounding population into a new animal. This property makes them an excellent model system to study the general rules of self-organization.

Mechanical oscillations orchestrate axial patterning through Wnt activation in .

Mechanical input shapes cell fate decisions during development and regeneration in many systems, yet the mechanisms of this cross-talk are often unclear. In regenerating tissue spheroids, periodic osmotically driven inflation and deflation cycles generate mechanical stimuli in the form of tissue stretching. Here, we demonstrate that tissue stretching during inflation is important for the appearance of the head organizer—a group of cells that secrete the Wnt3 ligand.

Self-Organization of Embryonic Genetic Oscillators into Spatiotemporal Wave Patterns.

In vertebrate embryos, somites, the precursor of vertebrae, form from the presomitic mesoderm (PSM), which is composed of cells displaying signaling oscillations. Cellular oscillatory activity leads to periodic wave patterns in the PSM. Here, we address the origin of such complex wave patterns.

Scaling of embryonic patterning based on phase-gradient encoding.

A fundamental feature of embryonic patterning is the ability to scale and maintain stable proportions despite changes in overall size, for instance during growth. A notable example occurs during vertebrate segment formation: after experimental reduction of embryo size, segments form proportionally smaller, and consequently, a normal number of segments is formed. Despite decades of experimental and theoretical work, the underlying mechanism remains unknown.

Autoregulatory and repressive inputs localize Hydra Wnt3 to the head organizer.

Polarized Wnt signaling along the primary body axis is a conserved property of axial patterning in bilaterians and prebilaterians, and depends on localized sources of Wnt ligands. However, the mechanisms governing the localized Wnt expression that emerged early in evolution are poorly understood. Here we find in the cnidarian Hydra that two functionally distinct cis-regulatory elements control the head organizer-associated Hydra Wnt3 (HyWnt3).

Three homologous subunits form a high affinity peptide-gated ion channel in Hydra.

Recently, three ion channel subunits of the degenerin (DEG)/epithelial Na(+) channel (ENaC) gene family have been cloned from the freshwater polyp Hydra magnipapillata, the Hydra Na(+) channels (HyNaCs) 2-4. Two of them, HyNaC2 and HyNaC3, co-assemble to form an ion channel that is gated by the neuropeptides Hydra-RFamides I and II. The HyNaC2/3 channel is so far the only cloned ionotropic receptor from cnidarians and, together with the related ionotropic receptor FMRFamide-activated Na(+) channel (FaNaC) from snails, the only known peptide-gated ionotropic receptor.

An Hh-dependent pathway in lateral plate mesoderm enables the generation of left/right asymmetry.

Breaking bilateral symmetry is critical for vertebrate morphogenesis. In the mouse, directional looping of the heart and rotation of the embryo, the first overt evidence of left/right asymmetry (L/R), are observed at early somite stages ( approximately E8.5) [1, 2].

Disp1 regulates growth of mammalian long bones through the control of Ihh distribution.

Dispatched1 (Disp1) is required for the release of cholesterol modified hedgehog (Hh) proteins from producing cells. We investigated the role of Disp1 in Indian hedgehog (Ihh) signaling in the developing bone bypassing the lethality of the Disp1(C829F) allele at early somite stages through the supply of non-cholesterol modified Sonic hedgehog (N-Shh). The long bones that develop in the absence of wild-type Disp1, while clearly shorter, have a juxtaposition of proliferating and non-proliferating hypertrophic chondrocytes that is markedly more normal in organization than those of ihh null mutants.