The Antarctic notothenioids is the most predominant fish clade in the Antarctic marine ecosystem. Evolving in the freezing temperatures for millions of years, a variety of genetic and physiological changes occurred to these fishes. A family of the notothenioids, Channichthyidae is well known for its extreme evolutionarily changes in the complete loss of hemoglobin and greately reduced circulating red blood cells. As a naturally occurred mutant, the icefish are regarded as good animal models for anemia, erythropoiesis and blood other disorders. So far the evolutionary and developmental mechanisms underlying the loss of red blood cells remianed to be investigated and the evolutionary significance of the red blood cell loss is unclear.
Researchers in Shanghai Ocean University recently reported new findings in these topics. By cross-species transcriptomic and microRNAome comparisons, they revealed substantial alterations in the expression of the genes involved in the hematopoietic process of the Antarctic ice fish. The alterations include strong inhibition of the essential hematopoietic factors, such as GATA1 and ALAS2, while up-regulation of hundreds of microRNAs in the hematopoietic tissue. The majority of the up-regulated microRNAs target the essential hematopoietic transcription factors. Remarkably, the transcriptional suppression and the microRNA upregulations were found to be partially attributable to the up-regulation of one signaling pathway, i.e., TGF-β pathway. Evolution analysis showed that positive selection has occurred to TGF-β1 and endoglin, the two important factors in the TGF-β pathway, specifically in the Antarctic clade of the notothenioid species. Such evolutionary pattern suggests that an evolutionary trend of up-regulating TGF-β signaling pathway occurred to all of the notothenioid lineages which occupied the freezing Antarctic waters besides the icefish lineage. This evolutionary trend might have led to a general trend of red blood cell reduction in the Antarctic notothenioids, and which has been more pronounced in the icefish. Thus, the study uncovered the molecular mechanisms underlying the red blood cell loss in the icefish and also pointed to a evolutionary mechanism of erythropioetic suppression in the fishes of freezing environment.
The work has been published online on September 6, 2015 on Molecular Ecology. Prof. Qianghua Xu from the College of Marine Science was the first author and Prof. Liangbiao Chen from the College of Fisheries and Life Science, together with Prof. Qianghua Xu, were the corresponding authors. Several graduate students, postdoctoral fellows and a number of staff members participated in this study. The study was sponsored by Natural Science Foundation of China, the Dawning Program, and the First-class Discipline Development Program in Aquaculture. The paper is available at: http://onlinelibrary.wiley.com/doi/10.1111/mec.13344/abstract