Successful cryopreservation of Pacific oyster (Crassostrea gigas) oocytes

Long-term study on survival and development of successive generations of Mytilus galloprovincialis cryopreserved larvae

Shellfish aquaculture needs the development of new tools for the improvement of good practices avoiding the reliance on natural spat collection to increase production efficiently. The aim of this work was to improve the cryopreservation protocol for Mytilus galloprovincialis larvae described in Paredes et al. (in: Wolkers, Oldenhof (eds) Cryopreservation and freeze-drying protocol, methods in molecular biology, Humana Press, 2021, pp 2180, 10.1007/978-1-0716-0783-1_18). Moreover, the capability of producing adult mussels from cryopreserved 72 h-old D-larvae and potential long-term effects of cryopreservation through progenies were evaluated. The selection of 72-h old D-larvae for cryopreservation yielded 75% of recovery, higher than 50% from trochophores. The best combination was 10% Ethylene–Glycol + 0.4 M Trehalose in Filtered Sea Water (FSW) with cooling at − 1 °C/min and a water bath at 35 °C for thawing. Sucrose (SUC) solutions did not improve larval recovery (p > 0.05). At settlement, 5.26% of cryopreserved F1 larvae survived and over 70% settled. F2 cryopreservation produced 0.15% survival of spat and settlement varied from 35 to 50%. The delay of shell size showed on cryopreserved larvae declined throughout larval rearing without significant differences with controls from settlement point (p > 0.05). Long-term experiments showed that it is possible to obtain adult mussels from cryopreserved larvae and this tool does not compromise the quality of following progenies, neither for cryopreservation nor post-thawing development of them.

Major challenges in cryopreservation of sea urchin eggs

Cryopreservation of gametes, embryos and larvae of marine invertebrates has been investigated in many studies throughout the years. There are many favorable studies on sperm cryopreservation but oocytes are still under research as no successful results have been sustainably obtained for this type of cells. The preservation of both maternal and paternal gametes separately would provide a reliable source of genetic material for their application to conservation, aquaculture and fundamental research. Unfortunately to date, it has not been possible to cryopreserve eggs from marine organisms. The aim of this review is to go over the factors that have been historically considered as obstacles for oocyte cryopreservation in aquatic organisms and discern those that may specifically apply to eggs of the sea urchin Paracentrotus lividus.

Development of a method to cryopreserve Greenshell mussel™ (Perna canaliculus) veliger larvae

Cryopreservation of larvae of Greenshell™ mussel Perna canaliculus, the most cultivated species in New Zealand, can provide flexibility for selective breeding programmes and enhance its global production. In this study, we set out to develop a reliable protocol for freezing D-stage larvae of Greenshell™ mussels that ensured long-term survival for successful rearing of thawed larvae in the hatchery. The effects of different combinations of cryoprotecting agents (CPA), varying CPA equilibration times, larval concentrations per straw as well as different larval development stages (48 h vs 72 h old) were evaluated by assessing the behavioural response (swimming activity, algal consumption), shell size and survival of larvae, up to 4 days post-thawing. The protocol yielding the best larval performances was a combination of the following CPA (final concentrations): 14% ethylene-glycol (EG) + 0.6 M trehalose (TRE) + 1% polyvinyl-pyrrolidone (PVP), prepared with Milli-Q water. Stocking densities ranging from 50,000 to 150,000 larvae per straw (0.25 mL) and a 20 min equilibration time gave the best results, while no significant differences in fitness were found between larvae cryopreserved at 48 h nor 72 h-old. Using the improved cryopreservation protocol, over 50% of previously cryopreserved D-larvae were able to survive after 4 days of rearing, compared with 65% in the unfrozen control. More importantly, about one third of thawed larvae were able to swim and feed, and to potentially develop further. These findings contribute to enhance the selective breeding programmes for this species.

First instance of settlement by cryopreserved coral larvae in symbiotic association with dinoflagellates

Coral reefs are suffering on a global scale due to human impacts, thereby necessitating cryopreservation efforts. The objective of this study was to develop a suitable vitrification and laser warming protocol for larvae of the scleractinian coral Seriatopora caliendrum, which inherit their dinoflagellate algal symbionts vertically. Toxicity experiments were conducted with the cryoprotectants (CPAs) ethylene glycol (EG), propylene glycol (PG), dimethyl sulfoxide (DMSO), glycerol (GLY), and methanol (METH; listed in order from least to most toxic), and larvae were subjected to vitrification and laser warming using 2 M EG + 1 M PG and 2 M EG + 1 M DMSO. Vitrification and laser warming (300 V, 10 ms pulse width, 2 mm beam diameter) using a vitrification solution of 2 M EG + 1 M PG, 40% w/v Ficoll, and 10% v/v gold nanobars (GNB) at a final concentration of 1.2 × 1018 GNB/mL and a characteristic wavelength of 535 nm resulted in larvae with vitality and settlement percentages of 55 and 9%, respectively. This represents the first successful instance of cryopreservation of coral larvae that proceeded to settle upon warming, and suggests that the vitrification and ultra-fast laser warming approach may be applicable to other threatened marine species.

A comparative proteomic analysis reveals important proteins for the fertilization and early embryonic development of the oyster Crassostrea gigas

Molluscan development involves important features that are important to understanding not only molluscan ontogeny but also animal evolution. To gain insight into the gamete proteome and protein function in fertilization and early development, we analyzed the proteomes of unfertilized oocytes and early embryos (2/4-cell stage) of the Pacific oyster, Crassostrea gigas. An oocyte reference map containing 116 protein spots, of which 69 were identified, revealed a high abundance of vitellogenin-derived protein spots. The differentially regulated protein spots during fertilization were screened using comparative proteomic approaches. In total, 18 differentially regulated protein spots were screened, and 15 of these were identified and divided into three groups. The proteins belonging to the first group function in energy supply and antioxidation and are proposed to ensure successful fertilization by regulating the levels of adenosine triphosphate, resisting oxidative stress, and preventing polyspermy. The proteins of the second group are associated with protein synthesis and modification, reflecting active protein synthesis after fertilization. The three proteins belonging to the final group are hypothesized to function in the regulation of embryonic development through the establishment of cell polarity and modulation of methylation reactions in nuclei. These results will enhance our knowledge of molluscan fertilization and development.

Cryobanking of aquatic species

This review is focused on the applications of genome cryobanking of aquatic species including freshwater and marine fish, as well as invertebrates. It also reviews the latest advances in cryobanking of model species, widely used by the scientific community worldwide, because of their applications in several fields. The state of the art of cryopreservation of different cellular types (sperm, oocytes, embryos, somatic cells and primordial germ cells or early spermatogonia) is discussed focusing on the advantages and disadvantages of each procedure according to different applications. A special review on the need of standardization of protocols has also been carried out. In summary, this comprehensive review provides information on the practical details of applications of genome cryobanking in a range of aquatic species worldwide, including the cryobanks established in Europe, USA, Brazil, Australia and New Zealand, the species and type of cells that constitute these banks and the utilization of the samples preserved.

STATEMENT OF RELEVANCE

This review compiles the last advances on germplasm cryobanking of freshwater and marine fish species and invertebrates, with high value for commercial aquaculture or conservation. It is reviewed the most promising cryopreservation protocols for different cell types, embryos and larvae that could be applied in programs for genetic improvement, broodstock management or conservation of stocks to guarantee culture production.

Towards a vitrification-based cryopreservation protocol for the coral Pocillopora damicornis L.: Tolerance of tissue balls to 4.5 M cryoprotectant solutions

In this study, we tested the tolerance of tissue balls (TBs, 100-400 μm in diameter) from the coral Pocillopora damicornis produced using mechanical excision to exposure to cryoprotectant (CPA) solutions. TBs were treated for 20 min at room temperature with individual, binary, ternary or quaternary CPA solutions with a total molarity from 2.0 to 5.0M. Four CPAs were used: ethylene glycol (EG), dimethylsulfoxide (Me2SO), methanol (Met) and glycerol (Gly). In some experiments, the molarity of the CPA solutions was increased and decreased in a stepwise manner. The tolerance of TBs following CPA treatment was evaluated using two parameters. The Tissue Ball Regression (expressed in μm/h) measured the diameter regression of TBs over time. The % Undamaged TBs quantified the proportion of TBs, which remained intact over time after the CPA treatment. TBs tolerated exposure to binary solutions with a total molarity of 4.0 M containing 2.0 M EG+2.0 M Met and 2.0 MEG+2.0 M Gly. TBs displayed tolerance to ternary solutions with a total molarity up to 3.0 M, containing each CPA at 1.0 M. Quaternary solutions with a total molarity of 4.0M containing each CPA at 1.0 M were not tolerated by TBs. When the molarity of the CPA solutions was increased and decreased in a stepwise manner, TBs withstood exposure to a CPA solution with a total molarity of 4.5 M, containing 1.5 M EG+1.5 M Gly+1.5 M Me(2)SO. This study confirmed the interest of using TBs to test CPA solutions, with the objective of developing a vitrification-based cryopreservation protocol.

Cryopreservation of Greenshell™ mussel (Perna canaliculus) sperm

Cryopreservation is a valuable technique for aquaculture as it enables a library or bank of genetically valuable animals to be maintained in a cost-effective manner. Here, we describe a method to cryopreserve the sperm of the Greenshell™ mussel (Perna canaliculus) and how to use the sperm post-thawing to maximize larval production from thawed sperm in selective breeding.

Survival, growth and reproduction of cryopreserved larvae from a marine invertebrate, the Pacific oyster (Crassostrea gigas)

This study is the first demonstration of successful post-thawing development to reproduction stage of diploid cryopreserved larvae in an aquatic invertebrate. Survival, growth and reproductive performances were studied in juvenile and adult Pacific oysters grown from cryopreserved embryos. Cryopreservation was performed at three early stages: trochophore (13±2 hours post fertilization: hpf), early D-larvae (24±2 hpf) and late D-larvae (43±2 hpf). From the beginning (88 days) at the end of the ongrowing phase (195 days), no mortality was recorded and mean body weights did not differ between the thawed oysters and the control. At the end of the growing-out phase (982 days), survival of the oysters cryopreserved at 13±2 hpf and at 43±2 hpf was significantly higher (P<0.001) than those of the control (non cryopreserved larvae). Only the batches cryopreserved at 24±2 hpf showed lower survival than the control. Reproductive integrity of the mature oysters, formely cryopreserved at 13±2 hpf and 24±2 hpf, was estimated by the sperm movement and the larval development of their offspring in 13 crosses gamete pools (five males and five females in each pool). In all but two crosses out of 13 tested (P<0.001), development rates of the offspring were not significantly different between frozen and unfrozen parents. In all, the growth and reproductive performances of oysters formerly cryopreserved at larval stages are close to those of controls. Furthermore, these performances did not differ between the three initial larval stages of cryopreservation. The utility of larvae cryopreservation is discussed and compared with the cryopreservation of gametes as a technique for selection programs and shellfish cryobanking.

Degradation of mitochondrial DNA in cryoprotectant-treated hard coral (Echinopora spp.) oocytes

A critical step for successful cryopreservation is to determine the optimal cryoprotectant treatment that can provide protective effects against cryoinjury during freezing and with minimal toxicity. Most cryoprotectants have chemical and osmotic effects when used at high concentrations. Cryoprotectants can damage coral mitochondrial distributions and membrane potentials, which results in reduced ATP production. As mitochondrial DNA (mtDNA) encodes for components of the electron transport chain (ETC) and plays a critical role in ATP synthesis capacity, we determined the effects of cryoprotectants on mtDNA in hard coral (Echinopora spp.) oocytes using quantitative real-time PCR. Our results showed that an insult from a cryoprotectant may be compensated for by the genetic defense mechanisms of these cells. Methanol was found to have the least effect on coral oocytes with regard to their energy status. A single oocyte without cryoprotectant treatment produced an average of 4,220,645 ± 169,990 mtDNA copies, which was greater than that in mammals. However, relatively lower mtDNA copy numbers (<2,000,000) were observed when oocytes were treated with dimethyl sulfoxide (DMSO), propylene glycol (PG), ethylene glycol (EG), or glycerol at a concentration of 3 M for 20 min. These results provide direct evidence that hard coral (Echinopora spp.) oocytes are extremely susceptible to cryoprotectants and support the concerns with regard to the adverse effects of cryoprotectants.

Cryopreservation of Greenshell™ mussel (Perna canaliculus) trochophore larvae

The Greenshell™ mussel (Perna canaliculus) is the main shellfish species farmed in New Zealand. The aim of this study was to evaluate the effects of cryoprotectant concentration, loading and unloading strategy as well as freezing and thawing method in order to develop a protocol for cryopreservation of trochophore larvae (16-20 h old). Toxicity tests showed that levels of 10-15% ethylene glycol (EG) were not toxic to larvae and could be loaded and unloaded in a single step. Through cryopreservation experiments, we designed a cryopreservation protocol that enabled 40-60% of trochophores to develop to D-larvae when normalized to controls. The protocol involved: holding at 0 °C for 5 min, then cooling at 1 °C min⁻¹ to -10 °C, holding for a further 5 min, then cooling at 0.5 °C min⁻¹ to -35 °C followed by a 5 min hold and then plunging into liquid nitrogen. A final larval rearing experiment of 18 days was conducted to assess the ability of these frozen larvae to develop further. Results showed that only 2.8% of the frozen trochophores were able to develop to competent pediveligers.

Setting tools for the early assessment of the quality of thawed Pacific oyster (Crassostrea gigas) D-larvae

Parameters used to assess the survival of larvae after cryopreservation generally misestimate the damages that prevent larval development. The objectives of the present study were to 1) define the reliability of the survival rate, assessed at 2 and 7 days post fertilization, to estimate Pacific oyster larval quality after thawing, and 2) select complementary tools allowing an early and reliable estimation of their quality. Oyster larvae were reared for 25 h after fertilization at 19 °C and cryopreserved at early D-stage. Then, thawed larvae were incubated in 2-L beakers. At 2 days post fertilization, the survival rate of thawed Pacific oyster larvae was lower than that of fresh larvae for only one experiment (Experiment 3) among the four identical experiments carried out in this work (Experiments 1-4). By contrast, the survival of thawed larvae, as assessed 7 days after fertilization, was lower than that of fresh larvae for the four experiments. These results confirm that the quality of thawed larvae is lower than that of fresh larvae and that the survival rate, estimated 2 days post fertilization, is not adapted to a reliable estimation of the subsequent development ability of thawed larvae. Then, complementary parameters were tested at 2 days: the movement characteristics (Experiments 1 and 2) and the morphologic features (Experiments 3 and 4) of thawed larvae. Compared to values observed on fresh larvae, the percentage of thawed motile larvae was different for only one experiment (Experiment 2) of the two. Compared to control, a reduced Average Path Velocity (VAP) of larvae (determined at the D-larval stage using a CASA-Computer Assisted Sperm Analysis-system) was observed after thawing for both experiments (Experiments 1 and 2), suggesting the ability of larval movement velocity to assess the decrease of the quality of thawed oyster larvae. Using an ASMA (Automated Sperm Morphology Analysis) device, a lower area of thawed larvae was observed, compared to control and for the two experiments (Experiments 3 and 4). By contrast, the Crofton perimeter of thawed larvae was lower than that of control larvae for only one experiment (Experiment 3) and no significant difference of circularity between fresh and thawed larvae was recorded for Experiments 3 and 4. In conclusion, changes in the movement velocity (assessed by CASA) and in the area (measured by ASMA) of D-larvae allow an early and reliable estimation of the quality of thawed Pacific oyster larvae.

Preserving and using germplasm and dissociated embryonic cells for conserving Caribbean and Pacific coral

Coral reefs are experiencing unprecedented degradation due to human activities, and protecting specific reef habitats may not stop this decline, because the most serious threats are global (i.e., climate change), not local. However, ex situ preservation practices can provide safeguards for coral reef conservation. Specifically, modern advances in cryobiology and genome banking could secure existing species and genetic diversity until genotypes can be introduced into rehabilitated habitats. We assessed the feasibility of recovering viable sperm and embryonic cells post-thaw from two coral species, Acropora palmata and Fungia scutaria that have diffferent evolutionary histories, ecological niches and reproductive strategies. In vitro fertilization (IVF) of conspecific eggs using fresh (control) spermatozoa revealed high levels of fertilization (>90% in A. palmata; >84% in F. scutaria; P>0.05) that were unaffected by tested sperm concentrations. A solution of 10% dimethyl sulfoxide (DMSO) at cooling rates of 20 to 30°C/min most successfully cryopreserved both A. palmata and F. scutaria spermatozoa and allowed producing developing larvae in vitro. IVF success under these conditions was 65% in A. palmata and 53% in F. scutaria on particular nights; however, on subsequent nights, the same process resulted in little or no IVF success. Thus, the window for optimal freezing of high quality spermatozoa was short (∼5 h for one night each spawning cycle). Additionally, cryopreserved F. scutaria embryonic cells had∼50% post-thaw viability as measured by intact membranes. Thus, despite some differences between species, coral spermatozoa and embryonic cells are viable after low temperature (-196°C) storage, preservation and thawing. Based on these results, we have begun systematically banking coral spermatozoa and embryonic cells on a large-scale as a support approach for preserving existing bio- and genetic diversity found in reef systems.

Biotechnologies for the management of genetic resources for food and agriculture

In recent years, the land area under agriculture has declined as also has the rate of growth in agricultural productivity while the demand for food continues to escalate. The world population now stands at 7 billion and is expected to reach 9 billion in 2045. A broad range of agricultural genetic diversity needs to be available and utilized in order to feed this growing population. Climate change is an added threat to biodiversity that will significantly impact genetic resources for food and agriculture (GRFA) and food production. There is no simple, all-encompassing solution to the challenges of increasing productivity while conserving genetic diversity. Sustainable management of GRFA requires a multipronged approach, and as outlined in the paper, biotechnologies can provide powerful tools for the management of GRFA. These tools vary in complexity from those that are relatively simple to those that are more sophisticated. Further, advances in biotechnologies are occurring at a rapid pace and provide novel opportunities for more effective and efficient management of GRFA. Biotechnology applications must be integrated with ongoing conventional breeding and development programs in order to succeed. Additionally, the generation, adaptation, and adoption of biotechnologies require a consistent level of financial and human resources and appropriate policies need to be in place. These issues were also recognized by Member States at the FAO international technical conference on Agricultural Biotechnologies for Developing Countries (ABDC-10), which took place in March 2010 in Mexico. At the end of the conference, the Member States reached a number of key conclusions, agreeing, inter alia, that developing countries should significantly increase sustained investments in capacity building and the development and use of biotechnologies to maintain the natural resource base; that effective and enabling national biotechnology policies and science-based regulatory frameworks can facilitate the development and appropriate use of biotechnologies in developing countries; and that FAO and other relevant international organizations and donors should significantly increase their efforts to support the strengthening of national capacities in the development and appropriate use of pro-poor agricultural biotechnologies.

Definition of fusion medium and electric parameters for efficient zygote electrofusion in the Pacific oyster (Crassostrea gigas)

Cell electrofusion has been widely used in the induction of tetraploidy in mammals, but little attention has been paid in molluscs. This work pursued the establishment of fusion medium (ionic vs. non-ionic) and electric parameters in the electrofusion of Pacific oyster zygotes (prior to the completion of the first mitotic division), minimizing all deleterious effects possible to D-larval stage. The tested combinations of electric field intensity (Vcm(-1)) and number of square DC pulses applied (for 50 micros each) were (Voltage x N degrees pulses): 400 x 1, 400 x 2, 400 x 3 and 600 x 1, 600 x 2, 600 x 3. When pulses were applied for first time, it was determined that an ionic fusion medium (microfiltered seawater) offered better conditions than the non-ionic fusion media previously used (0.6 M sucrose or 0.6 M mannitol) in terms of embryo survival and lysis rates. In this fusion medium, two different combinations of electric parameters (3 square DC pulses of 400 Vcm(-1) for 50 micros each at 26 degrees C and 1 square DC pulse of 600 Vcm(-1) for 50 micros at 26 degrees C) offered the best technical results of fusion (57 and 79% respectively) and survival until D-larva (44 and 41% respectively). In conclusion, these electric parameters could be established, using seawater as electrofusion medium, for further approaches to evaluate individual ploidy and survival beyond spat.

Cryopreservation of sea urchin embryos (Paracentrotus lividus) applied to marine ecotoxicological studies

Current strategies for marine pollution monitoring are based on the integration of chemical and biological techniques. The sea urchin embryo-larval bioassays are among the biological methods most widely used worldwide. Cryopreservation of early embryos of sea urchins could provide a useful tool to overcome one of the main limitations of such bioassays, the availability of high quality biological material all year round. The present study aimed to determine the suitability of several permeant (dimethyl sulfoxide, Me(2)SO; propylene glycol, PG; and ethylene glycol, EG) and non-permeant (trehalose, TRE; polyvinylpyrrolidone, PVP) cryoprotectant agents (CPAs) and their combination, for the cryopreservation of eggs and embryos of the sea urchin Paracentrotus lividus. On the basis of the CPAs toxicity, PG and EG, in combination with PVP, seem to be most suitable for the cryopreservation of P. lividus eggs and embryos. Several freezing procedures were also assayed. The most successful freezing regime consisted on cooling from 4 to -12 degrees C at 1 degrees C/min, holding for 2 min for seeding, cooling to -20 degrees C at 0.5 degrees C/min, and then cooling to -35 degrees C at 1 degrees C/min. Maximum normal larvae percentages of 41.5% and 68.5%, and maximum larval growth values of 42.9% and 60.5%, were obtained for frozen fertilized eggs and frozen blastulae, respectively.

Characterizing the freezing behavior of liposomes as a tool to understand the cryopreservation procedures

Freezing behaviors of egg yolk l-alpha-phosphatidylcholine (EPC) and 1,2-dipalmitoyl-rac-glycero-3-phosphocholine (DPPC) large unilamellar vesicles (LUV) were quantitatively characterized in relation to freezing temperatures, cooling rates, holding time, presence of sodium chloride and phospholipid phase transition temperature. Cooling of the EPC LUV showed an abrupt increase in leakage of the encapsulated carboxyfluorescein (CF) between -5 degrees C and -10 degrees C, which corresponded with the temperatures of the extraliposomal ice formation at around -7 degrees C. For the DPPC LUV, CF leakage started at -10 degrees C, close to the temperature of the extraliposomal ice formation; followed by a subsequent rapid increase in leakage between -10 degrees C and -25 degrees C. Scanning electron microscopy showed that both of these LUV were freeze-concentrated and aggregated at sub-freezing temperatures. We suggest that the formation of the extraliposomal ice and the decrease of the unfrozen fraction causes freeze-injury and leakage of the CF. The degree of leakage, however, differs between EPC LUV and DPPC LUV that inherently vary in their phospholipid phase transition temperatures. With increasing holding time, the EPC LUV were observed to have higher leakage when they were held at -15 degrees C compared to at -30 degrees C whilst leakage of the DPPC LUV was higher when holding at -40 degrees C than at -15 degrees C and -50 degrees C. At slow cooling rates, osmotic pressure across the bilayers may cause an additional stress to the EPC LUV. The present work elucidates freeze-injury mechanisms of the phospholipid bilayers through the liposomal model membranes.

Survival of Pacific oyster, Crassostrea gigas, oocytes in relation to intracellular ice formation

The effect of IIF in Pacific oyster oocytes was studied using cryo and transmission electron microscopy (TEM). The viability of oocytes at each step of a published cryopreservation protocol was assessed in an initial experiment. Two major viability losses were identified; one when oocytes were cooled to -35 degrees C and the other when oocytes were plunged in liquid nitrogen. Although the cryomicroscope showed no evidence of IIF in oocytes cooled with this protocol, TEM revealed that these oocytes contained ice crystals and were at two developmental stages when frozen, prophase and metaphase I. To reduce IIF, the effect of seven cooling programmes involving cooling to -35 or -60 degrees C at 0.1 or 0.3 degrees C min(-1) and holding for 0 or 30 min at -35 or -60 degrees C was evaluated on post-thaw fertilization rate of oocytes. Regardless of the cooling rate or holding time, the fertilization rate of oocytes cooled to -60 degrees C was significantly lower than that of oocytes cooled to -35 degrees C. The overall results indicated that observations of IIF obtained from cryomicroscopy are limited to detection of larger amounts of ice within the cells. Although the amount of cellular ice may have been reduced by one of the programmes, fertilization was reduced significantly; suggesting that there is no correlation between the presence of intracellular ice and post-thaw fertilization rate. Therefore, oyster oocytes may be more susceptible to the effect of high solute concentrations and cell shrinkage than intracellular ice under the studied conditions.

The bovine dominant ovarian follicle

Central roles in reproductive biology (i.e., growth and development of the oocyte, steroidogenesis, and ovulation) are played by the ovarian dominant follicle (DF). The DF is different from other follicles because it can escape atresia (the fate of all other follicles), and if exposed to the LH surge, its cells will differentiate into the corpus luteum. The DF was originally studied by looking at the surface of ovary through a surgical approach. Current studies employ a less-invasive ultrasound technique to track the growth and development of the DF. Recruitment and selection, the processes that give rise to the DF, and dominance, the physiological state of the mature DF, are important areas of basic research. Results of these basic studies are easily translated into real-world problems in farm animal reproduction. Superovulation, for example, overrides the selection mechanism and increases the number of ovulations. Understanding the factors that affect the size of the recruited pool should increase success rates (i.e., number of collected embryos) for superovulation. In most animals, the DF is short-lived, existing for long enough to allow for the final maturation of the oocyte. Some DF become atretic because they mature during the luteal phase and are never exposed to the LH surge. For other DF, the LH surge redirects the DF toward its ultimate demise (i.e., luteinization, ovulation, and differentiation into the corpus luteum). The DF is managed pharmacologically within protocols for timed AI. When timed AI fails, there may be abnormal corpus luteum development and early embryonic loss; outcomes that are secondary to inadequate follicular cell maturation and incomplete oocyte capacitation in the DF. Future work on the DF will clarify its underlying biological functions so that a variety of needs in farm animal reproduction can be efficiently managed.

Cold-loving microbes, plants, and animals--fundamental and applied aspects

Microorganisms, plants, and animals have successfully colonized cold environments, which represent the majority of the biosphere on Earth. They have evolved special mechanisms to overcome the life-endangering influence of low temperature and to survive freezing. Cold adaptation includes a complex range of structural and functional adaptations at the level of all cellular constituents, such as membranes, proteins, metabolic activity, and mechanisms to avoid the destructive effect of intracellular ice formation. These strategies offer multiple biotechnological applications of cold-adapted organisms and/or their products in various fields. In this review, we describe the mechanisms of microorganisms, plants, and animals to cope with the cold and the resulting biotechnological perspectives.

Assessment of gamete quality for the eastern oyster (Crassostrea virginica) by use of fluorescent dyes

Evaluation of sperm motility is the single most widely used parameter to determine semen quality in mammals and aquatic species. While a good indicator for fresh sperm viability, post-thaw motility is not always effective at predicting fertilizing ability. Techniques using fluorescent dyes can assess functionality of mammalian sperm, but have not been widely applied in aquatic organisms. The eastern oyster Crassostrea virginica is an important mollusk in the United States, and cryopreservation protocols have been developed to preserve sperm and larvae to assist research and hatchery production. In this study, protocols were developed to assess sperm cell membrane integrity and mitochondrial function by flow cytometry and to assess viability of eggs by fluorescence microscopy. The fluorescent dyes SYBR 14 and propidium iodide (PI) (to assess membrane integrity) and rhodamine 123 (R123) (to assess mitochondrial membrane potential) were used to evaluate the quality of thawed oyster sperm previously cryopreserved with different cryoprotectant and thawing treatments. Membrane integrity results were correlated with motility of thawed sperm and mitochondrial membrane potential with fertilizing ability. Fluorescein diacetate (FDA) was used to assess cytotoxicity of cryoprotectant solutions and post-thaw damage to oyster eggs. The results indicated that membrane integrity (P=0.004) and thawing treatments (P=0.04), and mitochondrial membrane potential (P=0.0015) were correlated with motility. Fertilizing ability was correlated with cryoprotectant treatments (P=0.0258) and with mitochondrial membrane potential (P=0.001). The dye FDA was useful in indicating structural integrity of fresh and thawed eggs. Exposure of eggs, without freezing, to dimethyl sulfoxide yielded higher percentages of stained eggs and fertilization rate than did exposure to propylene glycol (P=0.002). Thawed eggs were not stained with FDA (<1%) and larvae were not produced.