Amitosis-like nuclear division in erythrocytes of triploid rainbow trout Oncorhynchus mykiss

Absolute quantification of chromosome copy numbers in the polyploid macronucleus of Tetrahymena thermophila at the single-cell level

Amitosis is widespread among eukaryotes, but the underlying mechanisms are poorly understood. The polyploid macronucleus (MAC) of unicellular ciliates divides by amitosis, making ciliates a potentially valuable model system to study this process. However, a method to accurately quantify the copy number of MAC chromosomes has not yet been established. Here we used droplet digital PCR (ddPCR) to quantify the absolute copy number of the MAC chromosomes in Tetrahymena thermophila. We first confirmed that ddPCR is a sensitive and reproducible method to determine accurate chromosome copy numbers at the single-cell level. We then used ddPCR to determine the copy number of different MAC chromosomes by analyzing individual T. thermophila cells in the G1 and the amitotic (AM) phases. The average copy number of MAC chromosomes was 90.9 at G1 phase, approximately half the number at AM phase (189.8). The copy number of each MAC chromosome varied among individual cells in G1 phase and correlated with cell size, suggesting that amitosis accompanied by unequal cytokinesis causes copy number variability. Furthermore, the fact that MAC chromosome copy number is less variable among AM-phase cells suggests that the copy number is standardized by regulating DNA replication. We also demonstrated that copy numbers differ among different MAC chromosomes and that interchromosomal variations in copy number are consistent across individual cells. Our findings demonstrate that ddPCR can be used to model amitosis in T. thermophila and possibly in other ciliates.

Effects of triploid induction on innate immunity and hematology in Astyanax altiparanae

Triploid induction is a promising biotechnique that could be used to enhance aquaculture yields in the near future. However, studies conducted with several fish species have demonstrated that the presence of an extra set of chromosomes may result in deleterious health effects. Furthermore, studies of fish immune responses still need to be conducted before these specimens can be readily commercialized. In the study presented herein, we evaluated the effects of triploid induction on hematology, erythrocyte morphometry and morphology, phagocytosis, and the expression levels of IL-1β and TGF-β using specimens of the Neotropical species, Astyanax altiparanae. In general, the cell counts of erythrocytes, leukocytes, and neutrophils in triploid fish were lower than those in diploid fish. The erythrocytes of triploid fish were larger than those found in diploid fish, but also demonstrated considerably higher frequencies of cellular and nuclear abnormalities. Although not statistically significant, triploid induction resulted in a phagocytic capacity (PC) 20% lower than that found with diploid fish. No notable differences were observed in phagocytic index (PI). Gene expression levels for the cytokine IL-1 were lower in tissues from the head kidney, liver, and spleen of triploid fish with respect to diploid fish. Gene expression levels of TGF-β were lower only in the spleen of triploids compared to diploids. In conclusion, triploid induction resulted in A. altiparanae specimens with immune impairments and potentially lower resistances to disease and low-quality environments.

Differences in immune components of blood, spleen and head kidney between diploid and auto- and allotriploid Salmonidae

Immune components were investigated in peripheral blood and in spleen and head kidney of autotriploid Salmo trutta f. lacustris, Salvelinus fontinalis, and Salvelinus umbla, and of allotriploid hybrids of S. trutta f. lacustris x Onchorynchus mykiss and S. fontinalis x O. mykiss in comparison to their diploid parents. In peripheral blood the number of lymphocytes was reduced in all investigated autotriploids and in the allotriploid S. trutta f. lacustris x O.mykiss, and the numbers of thrombocytes in autotriploid S. trutta f. lacustris and in both allotriploids. Alternative pathway of complement activity and immunoglobulin concentration were significantly decreased in all investigated auto- and allotriploids, lysozyme activity in autotriploid S. fontinalis and in both allotriploids. In the spleen of the 3 autotriploids the number of erythrocytes was increased, while the number of lymphoid precursor cells was decreased. In their head kidney the erythrocytes numbers were decreased and the numbers of erythropoietic precursor cells and the melanomacrophage centers were increased. Contrary, cytology of spleen and head kidney of the two allotriploid hybrids was similar to diploid controls. Caspase 1, caspase 6, lysozyme, and acid phosphatase activity and immunoglobulin concentration of spleen and head kidney showed specific changes which were related to cytological results. These data indicate alterations in immune system and in lymphoid organs of auto- and allotriploid Salmonidae.

Amitosis of Polyploid Cells Regenerates Functional Stem Cells in the Drosophila Intestine

Organ fitness depends on appropriate maintenance of stem cell populations, and aberrations in functional stem cell numbers are associated with malignancies and aging. Symmetrical division is the best characterized mechanism of stem cell replacement, but other mechanisms could also be deployed, particularly in situations of high stress. Here, we show that after severe depletion, intestinal stem cells (ISCs) in the Drosophila midgut are replaced by spindle-independent ploidy reduction of cells in the enterocyte lineage through a process known as amitosis. Amitosis is also induced by the functional loss of ISCs coupled with tissue demand and in aging flies, underscoring the generality of this mechanism. However, we also found that random homologous chromosome segregation during ploidy reduction can expose deleterious mutations through loss of heterozygosity. Together, our results highlight amitosis as an unappreciated mechanism for restoring stem cell homeostasis, but one with some associated risk in animals carrying mutations.

Developmental toxicity of PAH mixtures in fish early life stages. Part I: adverse effects in rainbow trout

A new gravel-contact assay using rainbow trout, Oncorhynchus mykiss, embryos was developed to assess the toxicity of polycyclic aromatic hydrocarbons (PAHs) and other hydrophobic compounds. Environmentally realistic exposure conditions were mimicked with a direct exposure of eyed rainbow trout embryos incubated onto chemical-spiked gravels until hatching at 10 °C. Several endpoints were recorded including survival, hatching delay, hatching success, biometry, developmental abnormalities, and DNA damage (comet and micronucleus assays). This bioassay was firstly tested with two model PAHs, fluoranthene and benzo[a]pyrene. Then, the method was applied to compare the toxicity of three PAH complex mixtures characterized by different PAH compositions: a pyrolytic extract from a PAH-contaminated sediment (Seine estuary, France) and two petrogenic extracts from Arabian Light and Erika oils, at two environmental concentrations, 3 and 10 μg g(-1) sum of PAHs. The degree and spectrum of toxicity were different according to the extract considered. Acute effects including embryo mortality and decreased hatching success were observed only for Erika oil extract. Arabian Light and pyrolytic extracts induced mainly sublethal effects including reduced larvae size and hemorrhages. Arabian Light and Erika extracts both induced repairable DNA damage as revealed by the comet assay versus the micronucleus assay. The concentration and proportion of methylphenanthrenes and methylanthracenes appeared to drive the toxicity of the three PAH fractions tested, featuring a toxic gradient as follows: pyrolytic < Arabian Light < Erika. The minimal concentration causing developmental defects was as low as 0.7 μg g(-1) sum of PAHs, indicating the high sensitivity of the assay and validating its use for toxicity assessment of particle-bound pollutants.

Changes in hematological parameters of Cichlasoma dimerus (Teleostei, Perciformes) exposed to sublethal concentrations of 4-tert-octylphenol

Stress response involves various physiological changes, including alteration in hematological parameters closely related to the response of fish to the environment. 4-tert-octylphenol (OP) is one of the worldwide-used surfactants and can pollute the aquatic environment, both marine and freshwater. Previous studies have already shown estrogenic effects of this compound in various wildlife species, e.g., it can disrupt the reproductive system of males organisms including fish. The purpose of this study was to evaluate the effects caused by sublethal concentrations of OP on hematological parameters as biomarkers to assess environmental stress. Adult males and females of Cichlasoma dimerus were exposed to waterborne OP during 60 days under semistatic conditions. Experimental groups consisted of control (ethanol 0.005 %), OP 150, and OP 300 μg/L. OP caused hemodynamic stress in C. dimerus, which lead to normochromic and normocytic anemia, as well as erythrocytic pathologies such as a significant increase in erythroblasts and amitotic erythrocytes. All of the studied parameters can be used as biomarkers for the presence of xenobiotics in water.