Hydra--ancient model with modern outfit

Biotechnology in the treatment of sensorineural hearing loss: foundations and future of hair cell regeneration

PURPOSE

To provide an overview of the methodologies involved in the field of hair cell regeneration. First, the author provides a tutorial on the biotechnological foundations of this field to assist the reader in the comprehension and interpretation of the research involved in hair cell regeneration. Next, the author presents a review of stem cell and gene therapy and provides a critical appraisal of their application to hair cell regeneration. The methodologies used in these approaches are highlighted.

METHOD

The author conducted a narrative review of the fields of cellular, molecular, and developmental biology, tissue engineering, and stem cell and gene therapy using the PubMed database.

RESULTS

The use of biotechnological approaches to the treatment of hearing loss--approaches such as stem cell and gene therapy-has led to new methods of regenerating cochlear hair cells in mammals.

CONCLUSIONS

Incredible strides have been made in assembling important pieces of the puzzle that comprise hair cell regeneration. However, mammalian hair cell regeneration using stem cell and gene therapy are years--if not decades--away from being clinically feasible. If the goals of the biological approaches are met, these therapies may represent future treatments for hearing loss.

Nitric oxide pathway in lower metazoans

The presence of nitric oxide (NO) pathway has been well demonstrated in the main invertebrate groups, showing parallel findings on the role of NO in vertebrates and invertebrates. Noteworthy is the example of the role played by the nitrergic pathway in the sensorial functions, mainly in olfactory-like systems. On the other hand, the emerging molecular information about NOSs from lower metazoans (Porifera, cnidarians up to higher invertebrates) suggests that NO pathways might represent examples of a parallel evolution of the NOS prototypes in different animal lineages. Nevertheless, increasing evidence suggests that NO is one of the earliest and most widespread signaling molecules in living organisms. Here, we attempt to provide a survey of current knowledge of the synthesis and possible roles of NO and the related signaling pathway in lower metazoans (i.e., Porifera and Cnidaria), two phyla forming a crucial bridge spanning the evolutionary gap between the protozoans and higher metazoans. From the literature data here reported, it emerges that future research on the biological roles of NO in basal metazoans is likely to be very important for understanding the evolution of signaling systems.

Phenotypic plasticity in juvenile jellyfish medusae facilitates effective animal-fluid interaction

Locomotion and feeding in marine animals are intimately linked to the flow dynamics created by specialized body parts. This interaction is of particular importance during ontogeny, when changes in behaviour and scale challenge the organism with shifts in fluid regimes and altered functionality. Previous studies have indicated that Scyphozoan jellyfish ontogeny accommodates the changes in fluid dynamics associated with increasing body dimensions and velocities during development. However, in addition to scale and behaviour that-to a certain degree-underlie the control of the animal, flow dynamics are also dependent on external factors such as temperature. Here, we show phenotypic plasticity in juvenile Aurelia aurita medusae, where morphogenesis is adapted to altered fluid regimes imposed by changes in ambient temperature. In particular, differential proportional growth was found to compensate for temperature-dependent changes in viscous effects, enabling the animal to use adhering water boundary layers as 'paddles'-and thus economize tissue-at low temperatures, while switching to tissue-dominated propulsion at higher temperatures where the boundary layer thickness is insufficient to serve for paddling. This effect was predicted by a model of animal-fluid interaction and confirmed empirically by flow-field visualization and assays of propulsion efficiency.

Involvement of nitric oxide in the head regeneration of Hydra vulgaris

Recent data have shown that a functional NO-cGMP signalling system plays an important role during development and seems to be operative early during the differentiation of embryonic stem cells. The intriguing possibility exists that this role can be evolutionarily conserved between vertebrates and invertebrates. In this paper, we have analyzed the effect of NO-cGMP pathway on the regeneration process in Hydra vulgaris, the most primitive invertebrate possessing a nervous system. Our results indicate that NO production increased during Hydra regeneration. The NOS inhibitor L-NAME reduced the regenerative process and the same effect was obtained by treatment with either the specific guanylate cyclase inhibitor ODQ or the protein kinase G (PKG) inhibitor KT-5823. In contrast, the regeneration process was increased by treating decapitated Hydra with the NO donor NOC-18. Furthermore, we found that cell proliferation was also increased by treating decapitated Hydra with the NO donor NOC-18 and reduced by treatment with the NOS inhibitor L-NAME. Our results strongly suggest that the NO-cGMP-PKG pathway is involved in the control of the proliferative-differentiative patterns of developing and regenerating structures in cnidarians as well as bilaterians.