In zebrafish, there are no antecedents regarding the molecular profile of neutrophils, neither before nor after a harmful insult. Nevertheless, there is evidence that strongly suggests the existence of at least two neutrophils subpopulation during an inflammatory process. One neutrophils subset respond first and migrate to the affected area across the interstitial tissue and a second subset responds later and travels through the bloodstream to reach the insulted zone.
\(\sqrt{ }\)During embryonic and larval stages, in zebrafish coexist two types of neutrophils that have the ability to respond to a harmful stimulus at the same time, the primitive and definitive neutrophils. These two groups have different embryonic origin; primitive ones arise from the rostral blood island and definitive neutrophils from the caudal hematopoietic tissue. As a consequence, primitive neutrophils are tissue cells mainly located in the head region. On the contrary, definitive neutrophils preferably remain in the hematopoietic tissue at the ventral posterior region of the tail until activation.
Due to in our scenario neutrophils have different embryonic origin and body location that could implicate different surrounding signaling during inflammation, it is not clear what define the migratory behavior of this two neutrophils subpopulation. Owing to previous antecedents from our lab an others and preliminary results for these project, we propose the following hypothesis:
“The migration timing and migratory route of neutrophils during inflammation in zebrafish is defined depending on the embryonic origin they have (primitive or definitive) and did not rely on differently surrounding signals”
To corroborate our hypothesis we will take advantage of the existence of the transgenic line Tg(mpx:Dendra2), in which neutrophils are exclusively labeled and can be photo-converted from green to red. Thus, we will have, at the same time, primitive and definitive neutrophils differentially labeled (red and green respectively) and will monitor their behavior after a harmful stimulus in vivo in the whole organism. Using this strategy we will determine neutrophils specific timing response, route of migration and define if their reaction is conditioned by the surrounding signaling, exemplified here as different location respecting the affected area. Also, and to prove if these two subpopulations are different before the harmful stimulus or if they differentiate it, we will characterize their particular molecular profile in both situations.
This will be the first time that neutrophils subpopulation are characterized in zebrafish. Thus, our research will provide important and novel information that will contribute to filling this gap in neutrophils biology knowledge. Likewise, the data obtained in this work will allow comparing species at the opposite ends of the vertebrate phylum, zebrafish and mouse/human, to identify similarities and divergences in neutrophil biology. In addition, the progress in the understanding of the zebrafish immune response could be extendable to other teleost fish species, such salmon, and trout, and thus benefiting the aquaculture industry, a key aspect of the Chilean economy.
In a more general aspect and due to the crucial participation that neutrophils have in many chronic diseases, to improve the understanding of their subpopulatio

n origin, phenotype and function brings us closer to the moment in which we will develop therapies to selectively inhibit detrimental neutrophils subpopulation without interfering with the innate immune response.