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.
Highlights
Since fish air-breathing is an important evolutionary adaptation for aquatic hypoxia, it has fascinated researchers for at least a century [1,2,3]
We firstly compared the histological structures of barbels among loach M. anguillicaudatus, large-scale loach (P. dabryanus, a water–air bimodal respiration fish which can conduct air-breathing through its posterior intestine), zebrafish (Danio rerio, an aquatic breather), and yellow catfish (Pelteobagrus fulvidraco, an aquatic breather)
This study suggests that the loach barbel is a newly discovered fish air-breathing organ, and fn1b is closely involved in its air-breathing function
Summary
Since fish air-breathing is an important evolutionary adaptation for aquatic hypoxia, it has fascinated researchers for at least a century [1,2,3]. Along with the rapid development of sequencing, a very small number of studies have been performed on the transcriptome, microRNAome, and genome to reveal the molecular mechanisms of fish air-breathing formation and regulation [19]. In other words, is there another organ with a rich capillary network and a short gas diffusion distance, similar to the posterior intestine and skin in the loach, which can conduct air-breathing? We firstly compared the histological structures of barbels among loach M. anguillicaudatus (a water–air bimodal respiration fish), large-scale loach (P. dabryanus, a water–air bimodal respiration fish which can conduct air-breathing through its posterior intestine), zebrafish (Danio rerio, an aquatic breather), and yellow catfish (Pelteobagrus fulvidraco, an aquatic breather). Due to the nonlethal and regenerative characteristics of fish barbels [29,30] and the high efficiency of in vivo gene editing in loach M. anguillicaudatus [31], the loach barbel will be a good model for mechanistic investigations of fish air-breathing
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
