Effect of slow and ultra-rapid freezing on cell surface antigens of 8-cell mouse embryos

Ice nucleating agents allow embryo freezing without manual seeding

Embryo slow freezing protocols include a nucleation induction step called manual seeding. This step is time consuming, manipulator dependent and hard to standardize. It requires access to samples, which is not always possible within the configuration of systems, such as differential scanning calorimeters or cryomicroscopes. Ice nucleation can be induced by other methods, e.g., by the use of ice nucleating agents. Snomax is a commercial preparation of inactivated proteins extracted from Pseudomonas syringae. The aim of our study was to investigate if Snomax can be an alternative to manual seeding in the slow freezing of mouse embryos. The influence of Snomax on the pH and osmolality of the freezing medium was evaluated. In vitro development (blastocyst formation and hatching rates) of fresh embryos exposed to Snomax and embryo cryopreserved with and without Snomax was assessed. The mitochondrial activity of frozen-thawed blastocysts was assessed by JC-1 fluorescent staining. Snomax didn't alter the physicochemical properties of the freezing medium, and did not affect embryo development of fresh embryos. After cryopreservation, the substitution of manual seeding by the ice nucleating agent (INA) Snomax did not affect embryo development or embryo mitochondrial activity. In conclusion, Snomax seems to be an effective ice nucleating agent for the slow freezing of mouse embryos. Snomax can also be a valuable alternative to manual seeding in research protocols in which manual seeding cannot be performed (i.e., differential scanning calorimetry and cryomicroscopy).

Comparison of gene expression in fresh and frozen–thawed human preimplantation embryos

Identification and characterisation of differentially regulated genes in preimplantation human embryonic development are required to improve embryo quality and pregnancy rates in IVF. In this study, we examined expression of a number of genes known to be critical for early development and compared expression profiles in individual preimplantation human embryos to establish any differences in gene expression in fresh compared to frozen–thawed embryos used routinely in IVF. We analysed expression of 19 genes by cDNA amplification followed by quantitative real-time PCR in a panel of 44 fresh and frozen–thawed human preimplantation embryos. Fresh embryos were obtained from surplus early cleavage stage embryos and frozen–thawed embryos from cryopreserved 2PN embryos. Our aim was to determine differences in gene expression between fresh and frozen–thawed human embryos, but we also identified differences in developmental expression patterns for particular genes. We show that overall gene expression among embryos of the same stage is highly variable and our results indicate that expression levels between groups did differ and differences in expression of individual genes was detected. Our results show that gene expression from frozen–thawed embryos is more consistent when compared with fresh, suggesting that cryopreserved embryos may represent a reliable source for studying the molecular events underpinning early human embryo development.

Capacitation-like changes occur in mouse spermatozoa cooled to low temperatures

Previously we showed that >70% of mouse spermatozoa cooled slowly from 37 degrees C to 4 degrees C and warmed have undergone capacitation-like changes as examined by a chlortetracycline staining assay. These membrane changes are reflected in the ability of cooled spermatozoa to achieve fertilization rates in vitro similar to those of uncooled controls when added to oocytes immediately upon warming. The aim of this study was to determine the nature of these membrane changes. We found they were not dependent upon the rate of cooling to 4 degrees C and similar changes were observed when spermatozoa were cooled to higher temperatures (10 degrees and 20 degrees C), but it took longer for 50% of the spermatozoa to undergo such changes (3, 18, and 27 min for spermatozoa held at 4 degrees, 10 degrees, and 20 degrees C, respectively). Mixing cooled spermatozoa with oocytes immediately upon warming produced fertilization rates similar to fresh spermatozoa capacitated in vitro for 90 min before the oocytes were added. The rate of sperm penetration as determined by the fluorescent DNA stain Hoescht 33258 was also similar. However, the penetration time for cooled spermatozoa was significantly shortened when they were preincubated for 90 min before being added to oocytes. We conclude that membrane changes resembling capacitation (1) occur during cooling to temperatures above freezing, (2) are independent of cooling rate, (3) proceed faster at lower temperatures, and (4) obviate the need for prior capacitation in vitro before mixing with oocytes.

Carbohydrate antigen expression in murine embryonic stem cells and embryos. II. Sialylated antigens and glycolipid analysis

A mouse embryonic stem (ES) cell line E14 and early mouse embryos were stained with a panel of 15 monoclonal antibodies recognizing sialylated or potentially sialylated carbohydrate determinants. Sialyl Le-x and sialyl Le-a were detected on the pre-implantation embryo from the 8-cell stage, and sialyl Le-a weakly on undifferentiated ES cells. Changes in cell surface carbohydrates occurred after induction of ES cell differentiation with retinoic acid (RA) and dibutyryl cAMP. Qualitative analysis of the neutral glycolipids of untreated and RA-treated ES cells using high-performance thin-layer chromatography (HPTLC) revealed few differences between the two types of culture. The major gangliosides in both cultures were indicative of an active 'a' ganglioside synthesis pathway. GD3, a precursor of the 'b' synthesis pathway, previously reported to be characteristic of embryonal carcinoma (EC) cells, was absent. RA-induced differentiation caused a shift in the spectrum to more complex gangliosides. Application of fast atom bombardment mass spectrometry (FAB-MS) to permethylated derivatives of individual bands permitted partial characterization of an unusual sialylated glycolipid and a rare ganglioside with the suggested structure of GalNAc-GD1a.

Carbohydrate antigen expression in murine embryonic stem cells and embryos. I. Lacto and neo-lacto determinants

A comparative study of lacto- and neo-lacto series carbohydrate antigens between the undifferentiated and differentiated derivatives of the embryonic stem (ES) cell line E14 and expression in the early embryo is reported. Antibodies to neo-lacto and lacto (type 1 and 2) precursor chains and blood group antigens such as H (types 1 and 2) A, B and Lewis (Le-a, Le-b, Le-x, Le-y) were examined. Backbone lacto- and neo-lacto structures were present on undifferentiated cells, as were terminal alpha-gal, SSEA-1, Le-y and low levels of Le-a. On differentiation, Le-x (SSEA-1 determinant) disappeared as has been found for embryonal carcinoma (EC) cells, and other determinants became restricted to cells of particular morphology. These observations will aid determination of the status and phenotypic stability of long-term embryonic stem-cell cultures.