Abstract
Critically endangered sturgeons, having undergone three whole genome duplication events, represent an exceptional example of ploidy plasticity in vertebrates. Three extant ploidy groups, combined with autopolyploidization, interspecific hybridization and the fertility of hybrids are important issues in sturgeon conservation and aquaculture. Here we demonstrate that the sturgeon genome can undergo numerous alterations of ploidy without severe physiological consequences, producing progeny with a range of ploidy levels and extremely high chromosome numbers. Artificial suppression of the first mitotic division alone, or in combination with suppression of the second meiotic division of functionally tetraploid zygotes (4n, C-value = 4.15) of Siberian sturgeon Acipenser baerii and Russian sturgeon A. gueldenstaedtii resulted in progeny of various ploidy levels—diploid/hexaploid (2n/6n) mosaics, hexaploid, octoploid juveniles (8n), and dodecaploid (12n) larvae. Counts between 477 to 520 chromosomes in octoploid juveniles of both sturgeons confirmed the modal chromosome numbers of parental species had been doubled. This exceeds the highest previously documented chromosome count among vertebrates 2n ~ 446 in the cyprinid fish Ptychobarbus dipogon.
Highlights
Endangered sturgeons, having undergone three whole genome duplication events, represent an exceptional example of ploidy plasticity in vertebrates
We developed methods of artificial whole genome duplication (WGD) (AWGD) in functionally tetraploid species of Siberian and Russian sturgeon through suppression of the first mitotic division resulting in viable 8n juveniles
High embryonic and juvenile mortality rates is the greatest obstacle of such an approach[58], in diploid teleosts and in sturgeons, as reviewed by Havelka and Arai[59]. Such AWGD organisms may display altered cell architecture and genomic regulatory networks leading to dosage imbalances and abnormal expressions, as concluded by Yin et al.[60]
Summary
Endangered sturgeons, having undergone three whole genome duplication events, represent an exceptional example of ploidy plasticity in vertebrates. Additional lineage-specific WGD events have occurred independently in several teleostean lineages, e.g., 4R in B otiidae10, Catostomidae11, Cyprinidae12,13, Callichthyidae[14] and Salmonidae[15] These duplication events were associated with increased chromosome numbers from prevailing teleost 2n = 48–5016 to roughly (paleo)4n = 90–10417. The highest chromosome count of any vertebrate to date was documented in Ptychobarbus dipogon, a representative of the schizothoracine cyprinid lineage (Cypriniformes) from the Tibetan Plateau. Each metazoan organism that reproduces via fusion of haploid gametes into new diploid organism is biologically diploid, a mechanism associated with evolution of sexual reproduction, irrespective of evolutionary ploidy level of genome In this sense, biological and evolutionary polyploidy refers to different phenomena and the latter term is meaningful just in phylogenetic context. In this study we relate all ploidy levels to the functional scale i.e., normal Siberian and Russian sturgeon are functionally tetraploid, unless other scale specified
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