Modulation of amino acid transport in preimplantation mouse embryos by low concentrations of non-ionic and zwitterionic detergents

Analysis of stimulatory and inhibitory amino acids for development of hamster one-cell embryos in vitro

Hamster embryo development to the blastocyst stage in vitro can be modulated by amino acids. This series of experiments employed both empirically and statistically designed approaches to elucidate which of 20 amino acids inhibit or stimulate development and to devise a complement of amino acids that best supports in vitro development of hamster 1-cell embryos. Development and/or mean cell number were significantly inhibited by the presence of leucine, tyrosine, valine, isoleucine, phenylalanine, arginine, methionine, or cysteine (at 0.5 mM) and isoleucine, phenylalanine, or tryptophan (at 0.05 mM). Three amino acids--glutamine, taurine, and glycine--were stimulatory and in combination improved development; the culture medium containing these amino acids was designated Hamster Embryo Culture Medium-5. Moreover, addition of another eight amino acids--asparagine, aspartic acid, serine, glutamic acid, histidine, lysine, proline and cysteine (medium designated HECM-6)--had a significant stimulatory effect on development over previously formulated culture media for hamster embryos. These results demonstrated that amino acids, alone and in combination, can markedly stimulate or inhibit hamster embryo development in vitro up to the blastocyst stage. Embryo transfer experiments showed that HECM-5 and -6 (chemically defined, protein-free culture media) supported normal preimplantation embryo development in vitro. This study also indicates that empirically designed embryo culture media formulations can be as effective as those obtained by application of statistical methodologies.

Golden hamster embryonic genome activation occurs at the two-cell stage: correlation with major developmental changes

The earliest time of onset of embryonic genome activation in golden hamsters was investigated. The inhibition of transcription by alpha-amanitin (11 micrograms/ml) in cultured embryos resulted in a total arrest of development of early 2-cell embryos (26 hr post-egg activation); under similar conditions, immediate cleavage divisions of 1-, late 2-, 4-, and 8-cell embryos were not affected. Electrophoretic analysis of [35S]methionine-labeled embryonic proteins showed that alpha-amanitin treatment apparently inhibited transcription-dependent protein synthesis in early 2-cell and, to some extent, in late 2-cell when compared to 4-cell embryos. Analysis of total RNA synthesis, using [alpha 32P]-UTP or [32P]-orthophosphate, showed that there was a high proportion of radioactivity associated with the macromolecular fraction (RNA) at the early and late 2-cell stages and at the 4-cell stage compared to that at the 1-cell stage. These results indicate that the de novo synthesis of RNA, encoded by the embryonic genome, occurs at the 2-cell stage and that the second and subsequent cleavage divisions of hamster preimplantation embryos are dependent on new transcriptional activity. This initial activity of the embryonic genome in hamsters is coincident with several characteristic features of in vitro development such as a block to development, synthesis of major proteins, change in energy substrate preference, phosphate-inhibition of development and a requirement for amino acids.

Development of a noninvasive ultramicrofluorometric method for measuring net uptake of glutamine by single preimplantation mouse embryos

A noninvasive ultramicrofluorometric method for measuring net uptake of glutamine by single preimplantation mouse embryos is described. A linear relationship was found between fluorescence intensity of NADH produced and glutamine concentration (R2 = 0.985). Single embryos were placed in 20 nl drops of medium containing 0.5 mM glutamine, and the medium was sampled after 2 hr incubation at 37 degrees C. Changes in net glutamine uptake were determined in one-cell, two-cell, and eight-cell embryos and blastocysts incubated in medium containing no energy substrates (glucose, pyruvate, and lactate). The median glutamine uptake increased significantly from 0.480 and 0.270 pmoles/embryo/2 hr at the one-cell and two-cell stages, respectively, to 1.610 pmoles/embryo/2 hr at the blastocyst stage. Mean glutamine uptake was compared in the presence or absence of energy substrates at several developmental stages. A highly significant reduction of glutamine uptake in the presence of substrates was observed at the one-cell and two-cell stages of development. At the eight-cell stage, glutamine uptake was only marginally reduced in the presence of substrates, and no effect was found at the blastocyst stage. These data may partially explain the beneficial effect of glutamine on the culture of early mouse embryos through the two-cell block of development.

Membrane Alterations Induced by Amphiphiles

Amphiphilic compounds with distinct apolar and polar parts are readily intercalated into the erythrocyte membrane. When intercalated into the membrane, amphiphiles are probably orientated so that the polar head is at the polar-apolar interface of the lipid bilayer and the hydrophobic part within the apolar core of the bilayer. However, by virtue of their difference in molecular shape from the bulk lipids of the lipid bilayer, it is possible that the intercalated amphiphiles are partly segregated from bulk lipids and accumulate at protein-lipid interfaces in the bilayer, where the packing of the bilayer lipids may be less ordered.

Our studies show that amphiphiles, when intercalated into the erythrocyte membrane, trigger alterations in several membrane-connected functions. Some of the alterations induced (decreased osmotic fragility, increased passive potassium fluxes) seem to be due to non-specific interactions of the amphiphiles with the membrane, whereas other functions (ion transport mediated by membrane proteins, regulation of cell shape) seem to be sensitive to particular features of the amphiphiles.

Our studies indicate that the intercalation of amphiphiles into the erythrocyte membrane must involve rearrangements within the lipid bilayer. We have suggested that, when intercalated into the lipid bilayer, amphiphiles trigger a rapid formation of non-bilayer phases, which protect the bilayer against a collapse and bring about a trans-bilayer redistribution of intercalated amphiphiles as well as of bilayer lipids. At high sublytic concentrations, this process may also involve a release of microvesicles from the membrane.

The effect of cryopreservation on functional correlates of embryo integrity

To assess possible functional effects of the procedures involved in freezing/thawing of mammalian embryos, uptake of 3H-glycine and 125I-BSA (bovine serum albumin) was measured in mouse two-cell embryos and morulae before and after freezing. None of the procedures of dehydration, rehydration, or freezing affected glycine uptake significantly. Earlier results for uptake of 125I-BSA by fresh embryos which indicated an increase in endocytic activity between morula and blastocyst stages were confirmed, and hydrolysis of endocytosed 125I-BSA by morulae but not two-cell embryos was observed. Only 53 +/- 9% of two-cell embryos but 83 +/- 7% of morulae were apparently normal after freezing and thawing. Apparently normal frozen/thawed two-cell embryos were twice as active in 125I-BSA uptake as controls. This was not the case for morulae. The results suggest that freezing/thawing effects endocytotic processes in two-cell embryos but not morulae.

Neutral amino acid transport in embryonal carcinoma cells

Neutral amino acid transport was characterized in the pluripotent embryonal carcinoma (EC) cell line, OC15. Ten of the thirteen amino acids tested are transported by all three of the major neutral amino acid transport systems--A, L, and ASC--although one system may make a barely measurable contribution in some cases. The characterization of N-methyl-aminoisobutyric acid (meAIB) transport points to this model amino acid as a definitive substrate for System A transport by OC15 cells. Thus, high concentrations of meAIB can be used selectively to block System A transport, and the transport characteristics of meAIB represent system A transport. Kinetic analysis of System A, with a Km = 0.79mM and Vmax = 14.4 nmol/mg protein/5 min, suggests a single-component transport system, which is sensitive to pH changes. While proline transport in most mammalian cells is largely accomplished through System A, it is about equally divided between Systems A and ASC in OC15 cells, and System A does not contribute at all to proline transport by F9 cells, an EC cell line with limited developmental potential. Kinetic analysis of System L transport, represented by Na+-independent leucine transport, reveals a high-affinity, single-component system. This transport system is relatively insensitive to pH changes and has a Km = 0.0031 mM and Vmax = 0.213 nmol/mg protein/min. The putative System L substrate, 2-aminobicyclo-[2,2,1]heptane-2-carboxylic acid (BCH), inhibits Systems A and ASC as well as System L in OC15 cells. Therefore, BCH cannot be used as a definitive substrate for System L in OC15 cells. Phenylalanine is primarily transported by Na+-dependent Systems A and ASC (83% Na+-dependent; 73% System ASC) in OC15 cells, while it is transported primarily by the Na+-independent System L in most other cell types, including early cleavage stage mouse embryos and F9 cells. We have also found this unusually strong Na+-dependency of phenylalanine transport in mouse uterine blastocysts (82% Na+-dependent). There is no evidence for System N transport by OC15 cells, since histidine is transported primarily by a Na+-independent, BCH-inhibitable mechanism.