Delineating the roles of neutrophils and macrophages in zebrafish regeneration models

An inducible transgene reports activation of macrophages in live zebrafish larvae

Macrophages are the most functionally heterogenous cells of the hematopoietic system. Given many diseases are underpinned by inappropriate macrophage activation, macrophages have emerged as a therapeutic target to treat disease. A thorough understanding of what controls macrophage activation will likely reveal new pathways that can be manipulated for therapeutic benefit. Live imaging fluorescent macrophages within transgenic zebrafish larvae has provided a valuable window to investigate macrophage behavior in vivo. Here we describe the first transgenic zebrafish line that reports macrophage activation, as evidenced by induced expression of an immunoresponsive gene 1(irg1):EGFP transgene. When combined with existing reporter lines that constitutively mark macrophages, we reveal this unique transgenic line can be used to live image macrophage activation in response to the bacterial endotoxin lipopolysaccharide and xenografted human cancer cells. We anticipate the Tg(irg1:EGFP) line will provide a valuable tool to explore macrophage activation and plasticity in the context of different disease models.

Imaging innate immune responses at tumour initiation: new insights from fish and flies

Recent imaging studies in genetically tractable and translucent zebrafish and Drosophila melanogaster models have opened a window on the earliest stages of tumorigenesis, when pre-neoplastic cells first arise in tissues before they progress into full-blown cancers. Innate immune cells often find these cells soon after they develop, but this efficient surveillance is not always good for the host because although immune cells have phagocytic capacity, they can also nurture the growing clones of pre-neoplastic cells. We describe these newly observed early interactions between immune cells and cancer cells and speculate on their potential clinical implications.

Aloe vera bathing improved physical and humoral protection in breeding stock after induced spawning in matrinxã (Brycon amazonicus)

In this study, we show that induced spawning causes stress, an intense loss of epithelia and immunosuppression, decreasing physical and humoral protection in fish, effects that were prevented or improved in fish bathed with Aloe vera. A. vera has several medicinal properties, including wound healing and immunostimulatory effects, which we observed in this study. Fish bathed with A. vera had a higher number of epidermal goblet cells and, in general, an improved wound healing rate compared with the control after induced spawning. These effects might be related to (1) the stimulation of leukocyte activity, represented here by the increased leukocyte respiratory activity triggered by A. vera (leukocytes are recognized as playing an important role in wound repair); (2) the antimicrobial properties of A. vera, which decrease wound infection and accelerate the healing process; and (3) several mechanisms that explain the healing effect of A. vera (increased collagen synthesis, rate of epithelialization, and anti-inflammatory and moisturizing effects). Our results also suggest that caution is necessary during the induced spawning process, especially during stripping, and A. vera bathing is recommended after intensive aquaculture operations.

Using zebrafish as the model organism to understand organ regeneration

The limited regenerative capacity of several organs, such as central nervous system (CNS), heart and limb in mammals makes related major diseases quite difficult to recover. Therefore, dissection of the cellular and molecular mechanisms underlying organ regeneration is of great scientific and clinical interests. Tremendous progression has already been made after extensive investigations using several model organisms for decades. Unfortunately, distance to the final achievement of the goal still remains. Recently, zebrafish became a popular model organism for the deep understanding of regeneration based on its powerful regenerative capacity, in particular the organs that are limitedly regenerated in mammals. Additionally, zebrafish are endowed with other advantages good for the study of organ regeneration. This review summarizes the recent progress in the study of zebrafish organ regeneration, in particular regeneration of fin, heart, CNS, and liver as the representatives. We also discuss reasons of the reduced regenerative capacity in higher vertebrate, the roles of inflammation during regeneration, and the difference between organogenesis and regeneration.