A Flow Cytometry Protocol to Estimate DNA Content in the Yellowtail Tetra Astyanax altiparanae

Unraveling the role of satellite DNAs in the evolution of the giant XY sex chromosomes of the flea beetle Omophoita octoguttata (Coleoptera, Chrysomelidae)

BACKGROUND

The flea beetle Omophoita octoguttata (Coleoptera, Chrysomelidae) is a member of a group in which the males completely lack meiotic recombination (male-specific achiasmy) and that have extraordinarily large X and Y chromosomes. We combined genome sequencing, including microdissected Y and X chromosomes, and cytogenetic in situ hybridization studies, to evaluate the potential role of satellite DNAs (satDNAs) in the differentiation of those gigantic sex chromosomes.

RESULTS

We report flow cytometry results showing that this species has a very large genome size (estimated to be 4.61 and 5.47 pg, or roughly 4.6 and 5.5 gigabases, for males and females, respectively), higher than the estimates from two other Alticinae species without giant sex chromosomes, suggesting that these sequences have greatly expanded on both the sex chromosomes, and that the Y has not greatly shrunk like the ones of other insects such as Drosophila with male achiasmy. About 68% of this large genome is made up of repetitive DNAs. Satellite DNAs (OocSatDNAs) form ~ 8-9% of their genomes, and we estimate how much of the sex chromosome expansions occurred due to differential amplification of different satellite classes. Analysis of divergence between sequences in the X and Y chromosomes suggests that, during the past roughly 20 mya, different OocSatDNAs amplified independently, leading to different representations. Some are specific to the Y or X chromosome, as expected when males are achiasmate, completely preventing genetic exchanges between the Y and X.

Dried storage of sperm at supra-zero temperatures: An alternative for flow cytometric analysis under field conditions

In biotechnological processes such as chromosomal manipulation studies, semen has become a reference in the ploidy verification of the evaluated material. However, the use of fresh samples is limited to the use at field conditions because the analysis is performed under laboratory conditions. Thus, this study aimed to develop a simpler procedure for storing dry semen at 28 °C to reduce cold storage costs. For this, semen samples were evaluated according to established quality semen parameters, a protocol for dry, and 3 sterilization treatments of dry semen were applied to the store. The integrity of the DNA was evaluated every two months, using fresh semen, dry semen (untreated), and particles 3C to compare the peaks by flow cytometry. The results indicated that all samples evaluated before and after drying showed no significant difference in the DNA content. UV-treated semen showed a 1C peak in the histogram up to 180 days of storage and a non-significant difference (P > 0.05) from fresh control in the number of DNA particles up to 120 days and untreated only showed a 1C peak up to 120 days. The developed method may become an interesting procedure to serve as a reference peak for practical flow cytometric analysis, not only in the field of fish biology but also in biomedical and agricultural sciences. Furthermore, dried semen can become a tool for the preservation of genetic material and is a promising low-cost storage technique for biobanking.

All-triploid offspring in the yellowtail tetra Astyanax altiparanae Garutti & Britski 2000 (Teleostei, Characidae) derived from female tetraploid × male diploid crosses

This study aimed to evaluate the ploidy and survival of larvae resulting from crosses between tetraploid females and diploid males of yellowtail tetra Astyanax altiparanae, both females (three diploids and three tetraploids) and males (n = 3 diploids). Breeders were subjected to hormonal induction with pituitary gland extract from common carp fish (Cyprinus carpio). Females received two doses at concentrations of 0.3 and 3.0 mg/kg ^-1 body weight and at intervals of 6 h. Males were induced with a single dose of 3.0 mg/kg ^-1 applied simultaneously with the second dose in females. Oocytes from each diploid and tetraploid female were fertilized with semen from the same male, resulting in two crosses: cross 1 (diploid male and diploid female) and cross 2 (diploid male and tetraploid female). The procedures were performed with separate females (diploid and tetraploid) and diploid males for each repetition (n = 3). For ploidy determination, 60 larvae from each treatment were analyzed using flow cytometry and cytogenetic analyses. As expected, flow cytometry analysis showed that progenies from crosses 1 and 2 presented diploid and triploid individuals, respectively, with a 100% success rate. The same results were confirmed in the cytogenetic analysis, in which the larvae resulting from cross 1 had 50 metaphase chromosomes and those from cross 2 had 75 chromosomes. The oocytes have a slightly ovoid shape at the time of extrusion. Diploid oocytes had a size of 559 ± 20.62 μm and tetraploid of 1025.33 ± 30.91 μm. Statistical differences were observed between eggs from crosses 1 and 2 (P = 0.0130). No significant differences between treatments were observed for survival at the 2-cell stage (P = 0.6174), blastula (P = 0.9717), gastrula (P = 0.5301), somite (P = 0.3811), and hatching (P = 0.0984) stages. In conclusion, our results showed that tetraploid females of the yellowtail tetra A. altiparanae are fertile, present viable gametes after stripping and fertilization using the 'dry method', and may be used for mass production of triploids. This is the first report of these procedures within neotropical characins, and which can be applied in other related species of economic importance.

Establishing a model fish for the Neotropical region: The case of the yellowtail tetra Astyanax altiparanae in advanced biotechnology

The use of model organisms is important for basic and applied sciences. Several laboratory species of fishes are used to develop advanced technologies, such as the zebrafish (Danio rerio), the medaka (Oryzias latipes), and loach species (Misgurnus spp.). However, the application of these exotic species in the Neotropical region is limited due to differences in environmental conditions and phylogenetic distances. This situation emphasizes the establishment of a model organism specifically for the Neotropical region with the development of techniques that may be applicable to other Neotropical fish species. In this work, the previous research efforts are described in order to establish the yellowtail tetra Astyanax altiparanae as a model laboratory species for both laboratory and aquaculture purposes. Over the last decade, starting with artificial fertilization, the yellowtail tetra has become a laboratory organism for advanced biotechnology, such as germ cell transplantation, chromosome set manipulation, and other technologies, with applications in aquaculture and conservation of genetic resources. Nowadays, the yellowtail tetra is considered the most advanced fish with respect to fish biotechnology within the Neotropical region. The techniques developed for this species are being used in other related species, especially within the characins class.

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.

Simple Field Storage of Fish Samples for Measurement of DNA Content by Flow Cytometry

Flow cytometry is an effective and widely used tool for determination of ploidy in fish, but it is not always possible to access the fresh samples for analysis. We investigated the potential for extended storage of fish tissue with sterlet and tench as representative species of Chondrostei and Teleostei, using blood and fin of subadult/adult specimens and tail of larvae. Thirteen procedures for extending storage, selected for rapidity and simplicity in both field and laboratory conditions, were tested for each tissue sample. Flow cytometry was applied to fresh tissue immediately after sampling and to tissue subjected to experimental protocols, always along with species-specific standard, after 1, 5, and 10 days storage at 0-4°C or freezing at -80°C. The fluorochrome 4',6-diamidine-2'-phenylindole dihydrochloride was used with excitation/emission maximum 358/461 nm. Based on the measurability of stored samples, evaluation of directly measured coefficients of variation of their DNA peaks and the changes in fluorescence intensity compared to fresh tissue, optimal procedures for extended storage of the selected tissue types of the model species are suggested. © 2020 The Authors. Cytometry Part A published by Wiley Periodicals LLC. on behalf of International Society for Advancement of Cytometry.

Heat-induced triploids in Brycon amazonicus: a strategic fish species for aquaculture and conservation

Triploidization plays an important role in aquaculture and surrogate technologies. In this study, we induced triploidy in the matrinxã fish (Brycon amazonicus) using a heat-shock technique. Embryos at 2 min post fertilization (mpf) were heat shocked at 38°C, 40°C, or 42°C for 2 min. Untreated, intact embryos were used as a control. Survival rates during early development were monitored and ploidy status was confirmed using flow cytometry and nuclear diameter analysis of erythrocytes. The hatching rate reduced with heat-shock treatment, and heat-shock treatments at 42°C resulted in no hatching events. Optimal results were obtained at 40°C with 95% of larvae exhibiting triploidy. Therefore, we report that heat-shock treatments of embryos (2 mpf) at 40°C for 2 min is an effective way to induce triploid individuals in B. amazonicus.

Reproductive strategies and chromosomal aberrations affect survival in the Rivuliid fish Hypsolebias sertanejo

Rivulidae comprises a family of fish largely distributed in Brazil that includes 201 species, of which 125 are considered endangered. This fact emphasizes the need for development of conservation strategies including studies on genetics and reproduction. In this paper, we describe aspects of biology and reproduction of the rivuliid species Hypsolebias sertanejo. We outline the reproductive behaviour of this species under laboratory conditions, analyze ploidy status by flow cytometry, describe reproductive behaviour and performance and test dry and wet incubation of eggs. Although H. sertanejo showed well known patterns of reproductive behaviour, we verified many peculiarities inherent to its reproductive biology. As expected, most individuals were diploid (87.71%), however 14.29% were considered mosaics. Although no sterility was observed within mosaics, infertility of these fish was not fully evaluated. Hatching rate of the eggs collected was very low following both dry and wet incubation (5.04 and 3.79%, respectively). These results provide interesting information regarding the reproductive success of this species, and suggest that chromosomal abnormalities described may reduce the survival of H. sertanejo under natural conditions, limiting the perpetuation of this species, and emphasizing the need for more preservation efforts, including artificial propagation and gene banking.

Return temperature after heat shock affects the production of tetraploids in the yellowtail tetra Astyanax altiparanae

The aim of this study was to evaluate different post-shock temperatures for tetraploid induction in the yellowtail tetra Astyanax altiparanae. Newly fertilized eggs were divided into four groups, three were submitted to heat shock (40°C for 2 min) at 24 min post-fertilization (mpf) and another group remained without shock (control). Groups submitted to temperature shock were further separated at the following temperatures: 22°C, 26°C and 28°C. Survival among embryonic development was counted and at hatching the ploidy was analyzed by flow cytometry. The results showed that the post-shock temperature affects the parameters analyzed and, therefore, must be considered for optimization of the production of tetraploid in A. altiparanae. Those data are innovative and could be used in future studies of basic biology in this species.

Flow cytometric analysis from fish samples stored at low, ultra-low and cryogenic temperatures

Flow cytometry is a valuable tool in biomedical and animal sciences. However, equipment used for such analysis presents limitations at field conditions, suggesting then preservation procedures for future analysis at laboratory conditions. In this study, freezing at low (-20 °C), ultra-low (-80 °C) and cryogenic temperatures (-196 °C, i.e. liquid nitrogen) were used as preservation procedures of fish tissue. Samples were maintained in 0.9% NaCl or lysing solution, and stored at the temperatures above for 0 (fresh control), 60, 120 and 180 days of storage. After storage, the samples were thawed and proceeded to flow cytometric analysis. Storage at low temperatures (-20 °C), both in lysing and 0.9% NaCl, exhibited poor results when analyzed after 60, 120 and 180 days, showing noisy peaks, deviation in the DNA content and absence of peaks. Ultralow (-80 °C) and cryogenic (-196 °C) temperatures, both in lysing solution and 0.9% NaCl, showed good results and high quality of histograms. Both storage procedures gave similar histograms and DNA content in comparison with control group (fresh) even after 60, 120 and 180 days of storage, exhibiting the main peak at 2C content from diploid cells and a secondary peak at 4C derived from dividing cells. In conclusion, samples may be stored for 180 days at -80 °C and -196 °C in both, 0.9% NaCl or lysing solution. As cryogenic temperatures in liquid nitrogen permits indefinite storage, this procedure should be used for long-term preservation.

In vivo storage of oocytes leads to lower survival, increased abnormalities and may affect the ploidy status in the yellowtail tetra Astyanax altiparanae

SummaryIn this study we analyzed whether the in vivo storage of oocytes (time after ovulation until fertilization) affects the survival and the ploidy status of the yellowtail tetra Astyanax altiparanae. Fish were induced to spawn and, after ovulation, a small aliquot was stripped and immediately fertilized (positive control group). Subsequently, aliquots (~150 oocytes) were stripped and fertilized at various time points of 60, 120, 180 or 240 min. Developmental stages, abnormalities, survival and the ploidy status of the hatched larvae were examined. As expected, in the control group, 100% of the larvae were diploid. Conversely, triploid individuals were observed just at the 60 min treatment time point (0.6%). In vivo storage of oocytes also influenced the survival rates (P < 0.05); the 180 and 240 min samples, respectively, presented lower survival rates at gastrula (50.10±6.26% and 40.92±5.32%), and somite (17.80±5.14% and 4.41±2.76%) stages and lower hatching rates (12.01±4.04% and 4.41±2.76%). A higher percentage (99.27±0.40%) of normal larvae and only a few abnormal larvae (0.73±0.40%) were observed in the control group (P = 0.0000). This observation did not differ from that observed at the 60 min treatment point (P = 0.9976). A significant increase in the percentage of abnormalities was observed in the other treatments, and, after 240 min, the highest percentage of abnormal larvae was seen (P=0.0024; 83.33±16.67%). In conclusion, we showed that oocyte ageing had a significant effect on survival and may affect the ploidy status in A. atiparanae.

Genome size estimation of brackishwater fishes and penaeid shrimps by flow cytometry

Flow cytometry was used for estimating the genome size of five brackishwater finfish and four shrimp species. The genome size for Lutjanus argentimaculatus was 0.95 ± 0.10 and 0.79 ± 0.01 pg for Scatophagus argus. The genome sizes for Chanos chanos (0.72 ± 0.01 pg), Etroplus suratensis (1.71 ± 0.16 pg) and Liza macrolepis (0.87 ± 0.02 pg) which are important aquaculture species are reported for the first time in this study. The phylogenetic tree constructed using sixty-seven sequence accessions of cytochrome c oxidase subunit 1 (COI) gene of Lates calcarifer revealed two separate clades. The Indian Lates calcarifer species with estimated genome size of 0.44 ± 0.02 pg belonged to a clade different than that of South East Asia and Australia reported to have larger genome size. The genome size for the four major species of genus Penaeus (Penaeus monodon, Penaeus indicus, Penaeus vannamei and Penaeus japonicus) were found in similar range. The genome size of female shrimps ranged from 2.91 ± 0.03 pg (P. monodon) to 2.14 ± 0.02 pg (P. japonicus). In male shrimps, the genome size ranged from 2.86 ± 0.06 pg (P. monodon) to 2.19 ± 0.02 pg (P. indicus). Significant difference was observed in the genome size between male and female shrimp of all species except in P. monodon. The highest relative difference of 12.78% was observed in the genome size between the either sex in P. indicus. The interspecific relative difference of 30.59% in genome size was highest between the male shrimps of P. monodon and P. indicus and 35.98% between the female shrimps of P. monodon and P. japonicus. The stored gills and pleopod tissues could be successfully used up to 3 weeks to estimate the genome size in shrimps.