Antarctic Fish IgT, a Weird Option of Immunoglobulin Genes


Antarctic Fish IgT, a Weird Option of Immunoglobulin Genes

Antarctic fish, most of which belonging to the Perciform Suborder Notothenioidei, have acquired, during their evolution, specific features that allow them to thrive, at present, at cold and stable temperature (-1.86°C). Нe morphological evolution and diversification of Antarctic Notothenioid teleosts into over 120 species is one of the best examples of adaptive radiation in the marine environment. New ecological chances, for instance the extinction of antagonists, the colonization of vacant niches, or the emergence of key innovative features such as the gain of antifreeze glycoproteins have allowed them to live in cold habitats where other species would die. Нe evolution of the antifreeze glycoprotein genes from a trypsinogen-like gene is a striking innovation, in terms of genetic fitness, that guarantees the survival. However, in the course of their evolution, Antarctic fish have undergone also some “disaptations”, as mentioned by Montgomery and Clements, namely regressive changes or disappearance of traits in some species, such as the loss of erythrocytes and the hemoglobin in the Channichthyidae family, also known as icefish. Нey have completely lost the β-globin genes but maintain non-functional genomic remnants of α-globin genes.

Нe analysis of genome data from the Antarctic endemic fish provides a helpful information regarding processes that led to evolutionary adaptation, e.g. genome modifications and epigenetic control of gene expression, and that are crucial in influencing the capacity of Notothenioids to respond to striking environmental changes. However, despite a growing interest in the genome-wide study, it is not exhaustive enough to provide a clear picture because of the limited number of sequenced genomes. Over the last decade, there has been an explosion of molecular-based analyses, due to the development of high-throughput technologies, shedding light on the genomic basis of cold adaptation of Notothenioids. So, we have learned from integrative genomic and transcriptomic analyses that genome evolution, under constant cold conditions, has resulted in extensive expansions of specific gene families of utmost importance, since involved in reducing stress effects derived from cold temperatures. Нis was followed by an increase of gene expression and gene functions that contributed to physiological fitness of Antarctic Notothenioids under cold conditions, such as anti-oxidation, anti-apoptosis, lipid and protein metabolism, and immune response.

In view of these considerations, I think that Antarctic fish will never cease to amaze us by reinventing pre-existing genes with some novel as well as unique characteristics that are critically important for exerting their function in the constantly cold environment. However, there are still many dark side points awaiting clarification. For this reason, Antarctic fish certainly deserve considerable attention and further efforts to be investigated.

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