The role of proton transporters in epithelial Wnt signaling pathways

Regulation of epidermal stratification and development by basal keratinocytes

The epidermis is a stratified squamous epithelium distributed in the outermost layer of the skin and is intimately involved in the formation of a physical barrier to pathogens. Basal keratinocytes possess the properties of stem cells and play an essential role in epidermal development and skin damage recovery. Therefore, understanding the molecular mechanism of how basal keratinocytes participate in epidermal development and stratification is vital for preventing and treating skin lesions. During epidermal morphogenesis, the symmetric division of basal keratinocytes contributes to the extension of skin tissues, while their asymmetric division and migration facilitate epidermal stratification. In this review, we summarize the process of epidermal stratification and illustrate the molecular mechanisms underlying epidermal morphogenesis. Furthermore, we discuss the coordination of multiple signaling pathways and transcription factors in epidermal stratification, together with the roles of cell polarity and cell dynamics during the process.

Vacuolar H+-ATPases (V-ATPases) as therapeutic targets: a brief review and recent developments

Vacuolar H⁺-ATPases (V-ATPases) are multi-subunit enzymes that play housekeeping roles in eukaryotic cells by acidifying lysosomes, late endosomes, Golgi, and other membrane-bounded compartments. Beyond that, V-ATPases have specialized functions in certain cell types linked to diseases including osteoporosis and cancer. Efforts to identify strategies to develop inhibitors selective for V-ATPases that are involved in disease progression have been ongoing for more than two decades, but so far have not yielded a therapeutic agent that has been translated to the clinic. Recent basic science studies have identified unexpected roles for V-ATPases in nutrient and energy sensing, and renin/angiotensin signaling, which offer additional incentives for considering V-ATPases as therapeutic targets. This article briefly reviews efforts to utilize inhibitors of V-ATPases as drugs. Primary focus is on recent "rational" efforts to identify small molecule inhibitors of the V-ATPases that are selectively expressed in osteoclasts and cancer cells. Enoxacin and bis-enoxacin are two molecules that emerged from these efforts. These molecules block a binding interaction between V-ATPases and microfilaments that occurs in osteoclasts, but not most other cell types, which relates to the specialized function of V-ATPases in bone resorption. Enoxacin and bis-enoxacin have proven useful in the treatment of bone diseases and cancer in animal models and display therapeutic effects that are different, and perhaps better, than current drugs. These results provide evidence that agents targeting subsets of V-ATPases may prove useful in the clinic.

Establishment of lateral organ asymmetries in the invertebrate chordate, Ciona intestinalis

BACKGROUND

The evolutionary emergence and diversification of the chordates appear to involve dramatic changes in organ morphogenesis along the left/right axis. However, the ancestral chordate mechanism for establishing lateral asymmetry remains ambiguous. Additionally, links between the initial establishment of lateral asymmetry and subsequent asymmetries in organ morphogenesis are poorly characterized.

RESULTS

To explore asymmetric organ morphogenesis during chordate evolution, we have begun to characterize left/right patterning of the heart and endodermal organs in an invertebrate chordate, Ciona intestinalis. Here, we show that Ciona has a laterally asymmetric, right-sided heart. Our data indicate that cardiac lateral asymmetry requires H+/K+ ion flux, but is independent of Nodal signaling. Our pharmacological inhibitor studies show that ion flux is required for polarization of epidermal cilia and neurula rotation and suggest that ion flux functions synergistically with chorion contact to drive cardiac laterality. Live imaging analysis revealed that larval heart progenitor cells undergo a lateral shift without displaying any migratory behaviors. Furthermore, we find that this passive shift corresponds with the emergence of lateral asymmetry in the endoderm, which is also ion flux dependent.

CONCLUSIONS

Our data suggest that ion flux promotes laterally asymmetric morphogenesis of the larval endoderm rudiment leading to a passive, Nodal-independent shift in the position of associated heart progenitor cells. These findings help to refine hypotheses regarding ancestral chordate left/right patterning mechanisms and how they have diverged within invertebrate and vertebrate chordate lineages.

Electrochemical regulation of cell polarity and the cytoskeleton

Cell polarity plays a key role in regulating cell-cell communication, tissue architecture, and development. Both internal and external cues participate in directing polarity and feedback onto each other for robust polarization. One poorly appreciated layer of polarity regulation comes from electrochemical signals spatially organized at the level of the cell or the tissue. These signals which include ion fluxes, membrane potential gradients, or even steady electric fields, emerge from the polarized activation of specific ion transporters, and may guide polarity in wound-healing, development or regeneration. How a given electrochemical cue may influence cytoskeletal elements and cell polarity remains unclear. Here, we review recent progress highlighting the role of electrochemical signals in cell and tissue spatial organization, and elucidating the mechanisms for how such signals may regulate cytoskeletal assembly for cell polarity.