Lactate dehydrogenase isozymes in mouse blastocyst cultures

Preimplantation embryo gene expression: 56 years of discovery, and counting

The biology of preimplantation embryo gene expression began 56 years ago with studies of the effects of protein synthesis inhibition and discovery of changes in embryo metabolism and related enzyme activities. The field accelerated rapidly with the emergence of embryo culture systems and progressively evolving methodologies that have allowed early questions to be re-addressed in new ways and in greater detail, leading to deeper understanding and progressively more targeted studies to discover ever more fine details. The advent of technologies for assisted reproduction, preimplantation genetic testing, stem cell manipulations, artificial gametes, and genetic manipulation, particularly in experimental animal models and livestock species, has further elevated the desire to understand preimplantation development in greater detail. The questions that drove enquiry from the earliest years of the field remain drivers of enquiry today. Our understanding of the crucial roles of oocyte-expressed RNA and proteins in early embryos, temporal patterns of embryonic gene expression, and mechanisms controlling embryonic gene expression has increased exponentially over the past five and a half decades as new analytical methods emerged. This review combines early and recent discoveries on gene regulation and expression in mature oocytes and preimplantation stage embryos to provide a comprehensive understanding of preimplantation embryo biology and to anticipate exciting future advances that will build upon and extend what has been discovered so far.

Effects of oxygen tension on the establishment and lactate dehydrogenase activity of murine embryonic stem cells

The lack of a standardized culture environment for establishment of embryonic stem cell lines has hindered the orchestrated differentiation of cells and the application of this technology. Oxygen concentration has a profound effect on proliferation and differentiation of many cell types. This study tested the hypothesis that establishment dynamics, lactate dehydrogenase (LDH) isoforms, and mRNA expression patterns would be affected by the oxygen tension in the culture environment. Recovered (day 4) murine blastocysts were cultured in a gas environment of 6% CO(2) and either 20% or 5% O(2) (balance supplemented with N(2)). More (p < 0.05) blastocysts produced outgrowths in the low (79.3 +/- 0.1%) compared to the high (57.1 +/- 0.1%) O(2) groups, and more (p < 0.05) colonies in the low O(2) group (14/15; 93.3 +/- 0.1%) stained positive for alkaline phosphatase relative to the high O(2) group (9/15; 60.6 +/- 0.1%). Oxygen treatment had no effect on the activity of the oxioreductase lactate dehydrogenase. Interestingly, the stem cell lines in both treatments displayed multiple isoforms (III, IV, and V) of LDH, whereas the outgrowths displayed isoforms I and V. In contrast, two-cell embryos and blastocysts displayed only isoform I, and fibroblasts displayed isoforms IV and V. There were no treatment differences in mRNA expression of LDHalpha in the outgrowths, or established stem cells. LDH transition from the heart (I) to the muscle (V) isoform indicated an increase in glycolytic activity, consistent with the peri-hatching/implantation time period. Reduced O(2) environment had significant positive effects on the establishment and maintenance of murine stem cells, supporting the hypothesis, whereas the LDH isozyme transition was consistent among treatments.

Lactate regulates pyruvate uptake and metabolism in the preimplantation mouse embryo

This study was an investigation of the interaction of lactate on pyruvate and glucose metabolism in the early mouse embryo. Pyruvate uptake and metabolism by mouse embryos were significantly affected by increasing the lactate concentration in the culture medium. In contrast, glucose uptake was not affected by lactate in the culture medium. At the zygote stage, the percentage of pyruvate taken up and oxidized was significantly reduced in the presence of increasing lactate, while at the blastocyst stage, increasing the lactate concentration increased the percentage of pyruvate oxidized. Lactate oxidation was determined to be 3-fold higher (when lactate was present at 20 mM) at the blastocyst stage compared to the zygote. Analysis of the kinetics of lactate dehydrogenase (LDH) determined that while the V(max) of LDH was higher at the zygote stage, the K(m) of LDH was identical for both stages of development, confirming that the LDH isozyme was the same. Furthermore, the activity of LDH isolated from both stages was reduced by 40% in the presence of 20 mM lactate. The observed differences in lactate metabolism between the zygote and blastocyst must therefore be attributed to in situ regulation of LDH. Activity of isolated LDH was found to be affected by nicotinamide adenine dinucleotide(+) (NAD(+)) concentration. In the presence of increasing concentrations of lactate, zygotes exhibited an increase in autofluorescence consistent with a depletion of NAD(+) in the cytosol. No increase was observed for later-stage embryos. Therefore it is proposed that the differences in pyruvate and lactate metabolism at the different stages of development are due to differences in the in situ regulation of LDH by cytosolic redox potential.

Changes in requirements and utilization of nutrients during mammalian preimplantation embryo development and their significance in embryo culture

Along with the transition from maternal to embryonic genome control the mammalian preimplantation embryo undergoes significant changes in its physiology during development. Concomitant with these changes are altering patterns of nutrient uptake and differences in the subsequent fate of such nutrients. The most significant nutrients to the developing mammalian preimplantation embryo are carbohydrates and amino acids, which serve not only to provide energy but also to maintain embryo function by preventing cellular stress induced by suboptimal culture conditions in vitro. It is subsequently proposed that optimal development of the mammalian embryo in culture requires the use of two or more media, each designed to cater for the changing requirements of the embryo. Importantly, culture conditions that maintain the early embryo are not ideal for the embryo post-compaction, and conditions that support excellent development and differentiation of the blastocyst can actually be inhibitory to the zygote. A marker of in vitro-induced cellular stress to the embryo is the relative activity of the metabolic pathways used to generate energy for development. Quantification of embryo energy metabolism may therefore serve as a valuable marker of embryo development and viability.

Gene expression during oogenesis in mice

A mouse egg is the end-product of oogenesis--a process initiated during fetal development and completed months later at the time of sperm-egg fusion. Oogenesis includes many important events. Among these are formation of female germ cells, initiation and completion of meiosis, and establishment of a maternal store of materials to support fertilization and preimplantation development. The latter takes place largely during germ cell growth in sexually mature females and involves extensive gene expression. Ribonucleic acid and protein accumulate to unusually high levels during this relatively short phase of oogenesis. Recent studies have demonstrated that establishment of a maternal store of materials in the growing mouse egg is both transcriptionally and translationally regulated. Specific examples of both types of regulation are presented here in the context of gene expression during oogenesis in mice.

Influence of embryo size on lactate dehydrogenase isozyme expression in giant mouse chimaeras

Chimaeras consisting of 2, 4, 8 and up to 16 mouse embryos were formed at day 3 and cultured in vitro up to day 8. The influence of size and cell number on the activation of the embryonic genome for LDH-5 was studied in non-attaching giant chimaeric blastocysts and compared to control embryos implanting in vivo or growing out in vitro. Day 5 chimaeric blastocysts consisting of 4 to 8 embryos had a similar size as early in vivo egg cylinders, but still expressed exclusively LDH-1 as normal preimplantation embryos do. Only during further ageing of non-attaching chimaeric blastocysts, a few samples were positive for LDH-5. There is no convincing evidence that the experimental increase of the cell number triggers a premature activation of the embryonic LDH genes. These results are discussed in comparison to other possible mechanisms regulating stage-specific activation of the embryonic genome.

The ontogenic characteristics of lactate dehydrogenase isozymes in mammaliam pre-implantation ova

The onotgenic characteristics of lactate dehydrogenase (LDH) isozymes in mammalian pre-implantation ova have been reviewed. Evidence has been provided that the ova of mice and other mammalian species contain enzyme activity in a masked form, and display turnover processes which possess distinctive characteristics by comparison with those in adult tissues. Also, the extraordinary high levels of LDH in the extracellular secretion of the mammaliam oviduct have been commented on, along with the influence of reproductive hormones on the activity and type of this enzyme. In addition, attention has been drawn to the unique characteristics of the oval micro-evironment, and the influence which such factors may exert on the realization of enzyme phenotype during early mammalian development.

Expression of lactate dehydrogenase isozyme 5 (LDH-5) in cultured mouse blastocysts in the absence of implantation and outgrowth

Extensive extraction studies with Triton X-100 revealed only LDH-1 (B4) but no trace of LDH-5 (A4) in one-cell and two-cell mouse and rat embryos. The LDH isozyme pattern of preimplantation mouse embryos changes from the maternally inherited B subunit isozyme (LDH-1) to a pattern dominated by LDH-5 when mouse blastocysts are cultured under conditions that prevent hatching but allow trophoblast giant cell transformation. During differentiation of mouse blastocysts in vitro, implantation is therefore not essential for the appearance of the A subunit form of LDH (LDH-5) coded for by the embryonic genome. Mechanisms controlling the expression of LDH-5 in mouse blastocysts during in vivo development are discussed.

Evidence for the lack of feedback regulation of gene activity and for the absence of subunit exchange between lactate dehydrogenase tetramers in vivo

Frog and rat lactate dehydrogenase (LDH, L-lactate:NAD+ oxidoreductase, EC 1.1.1.27) isozymes, highly purfied by affinity chromatography, were injected into newly fertilized from (Rana pipiens) eggs to study the effect of the injected isozymes on the expression of the LDH genes of the developing frog embryo. From these experiments three conclusions can be drawn: (i) homologous and heterologous LDH, even when present in more than twice the normal amount of LDH, does not play any role in the switching on or off of the frog LDH genes or in regulating the level of gene activity. No evidence was found in support of any feedback regulation of LDH synthesis by the LDH molecule itself. (ii) Injected rat LDH is very stable in the frog embryo, and the contrary to what can be demonstrated in vitro, all the isozymes show the same stability. No evidence was found for selective degradation of any of the injected five isozymes. (iii) The fact that the injected isozymes disappear 12 days after the injection without forming hybrid molecules between themselves or with the stored or newly synthesized frog LDH is evidence in favor of the hypothesis that the tetramer is the degradative unit of LDH, not the monomer as others have postulated. The LDH tetramers do not dissociate the recombine under the physiological conditions present in frog cells.