Fibronectin 1B Gene Plays an Important Role in Loach Barbel Air-Breathing

Abstract

Loach (Misgurnus anguillicaudatus) is well known to perform air-breathing through the posterior intestine and skin. However, we find here for the first time a unique central vascular structure in the loach barbel, with a blood–gas diffusion distance as short as that of the posterior intestine. Under acute hypoxia, the distance of loach barbels became significantly shorter. Moreover, barbel removal significantly decreased air-breathing frequency of the loach. These findings imply that the barbel is another air-breathing organ of the loach. For further investigation of loach barbel air-breathing, a transcriptome analysis of barbels with air exposure treatment was performed. A total of 2546 differentially expressed genes (DEGs) between the T-XU (air exposure) and C-XU (control) group were identified, and 13 key DEGs related to barbel air-breathing were screened out. On this foundation, sequence, expression, and location analysis results indicated an important positive role of fibronectin 1b (fn1b) in loach barbel air-breathing. We further generated an fn1b-depletion loach (MT for short) using the CRISPR/Cas9 technique. It was indicated that depletion of fn1b could weaker barbel air-breathing ability. In conclusion, due to nonlethal and regenerative characteristics, the loach barbel, a newly discovered and fn1b-related fish air-breathing organ, can be a good model for fish air-breathing research.

The loach (Misgurnus anguillicaudatus) genome and the adaptation to a mud environment

“…Oxygen is vital for the survival of most life forms. With various ABOs, M. anguillicaudatus markedly enhances its hypoxic tolerance to the bottom mud, providing a good model for studying the evolution of benthic adaptability in the accessory respiratory organs (Sun et al 2021;Huang et al 2022;Huang et al 2021). Here, we found that oxygen transport-related GO categories (oxygen binding (GO:0019825, P = 3.11E-12), gas transport (GO:0015669, P = 1.48E-12), oxygen transport (GO:0015671, P = 1.48E-12) and hemoglobin complex (GO:0005833, P = 2.86E-13)) significantly expanded in the loach genome ( Table S2-(3)).…”

“…To better identify air-breathing-related genes of the loach, on the basis of our previous studies including developmental transcriptome analysis of loach posterior intestines , intestinal air-breathing inhibition trial (transcriptome ) and microRNAs ) analysis), comparative transcriptome analysis of posterior intestines between the loach and non-air-breathing L. elongata (Huang et al 2022), an air exposure trial (namely, an intestinal air-breathing enhancement trial) was performed and the procedures in details were described as Sun et al (Sun et al 2021). A total of 18 WT loaches were used for transcriptome analysis.…”

“…Interestingly, some fish species, such as M. anguillicaudatus, Ophiocephalus argus and Protopterus annectens, have evolved accessory airbreathing organs (ABOs) to adapt to anoxic environments (Wang et al 2021;Jiang et al 2016). In addition to gill respiration, M. anguillicaudatus uses various ABOs including the posterior intestine, skin and barbel, to do air-breathing and maintain their blood oxygen saturation (Sun et al 2021). M. anguillicaudatus has become a valuable model for investigating the evolution of benthic adaptability in the ABOs (Sun et al 2021;.…”

“…In addition to gill respiration, M. anguillicaudatus uses various ABOs including the posterior intestine, skin and barbel, to do air-breathing and maintain their blood oxygen saturation (Sun et al 2021). M. anguillicaudatus has become a valuable model for investigating the evolution of benthic adaptability in the ABOs (Sun et al 2021;.…”

The chromosome-level genome and key genes associated with mud-dwelling behavior and adaptations of hypoxia and noxious environments in loach (Misgurnus anguillicaudatus)

“…Interestingly, some fish species, such as M. anguillicaudatus , Ophiocephalus argus , and Protopterus annectens , have evolved accessory air-breathing organs (ABOs) to adapt to anoxic environments [ 9 – 11 ]. Specifically, M. anguillicaudatus uses multiple ABOs including posterior intestine, skin, and barbel, to do air-breathing to maintain their blood oxygen saturation [ 12 ]. M. anguillicaudatus has become an appropriate model for investigating the evolution of benthic adaptability in the ABOs [ 12 , 13 ].…”