Cryopreservation of animal oocytes and embryos: current progress and future prospects

Cryopreservation describes techniques that permit freezing and subsequent warming of biological samples without loss of viability. The application of cryopreservation in assisted reproductive technology encompasses the freezing of gametes, embryos and primordial germ cells. Whilst some protocols still rely on slow-freezing techniques, most now use vitrification, or ultra-rapid freezing, for both oocytes and embryos due to an associated decreased risk of damage caused by the lack of ice crystal formation, unlike in slow-freezing techniques. Vitrification has demonstrated its use in many applications, not only following in vitro fertilisation (IVF) procedures in human embryology clinics, but also following in vitro production (IVP) of embryos in agriculturally important, or endangered animal species, prior to embryo transfer. Here we review the various cryopreservation and vitrification technologies that are used in both humans and other animals and discuss the most recent innovations in vitrification with a particular emphasis on their applicability to animal embryology

Preferential association of apolipoprotein E Leiden with very low density lipoproteins of human plasma

Apolipoprotein (apo) E Leiden is a rare variant of human apoE characterized by defective receptor binding and associated with dominant transmission of type III hyperlipoproteinemia. In heterozygotes, apoE Leiden is present in higher concentrations in both total plasma and very low density lipoproteins (VLDL) than the other apoE allele product. In the present study we analyzed cell expression and plasma lipoprotein association of apoE Leiden to determine whether the unequal concentration of the two apoE allele products could be explained by differences in secretion rate from the hepatocyte or by preferential association with VLDL. We transfected the rat hepatoma cell line McA-RH7777 with apoE Leiden or normal human apoE3, and studied their secretion and media distribution. In pulse-chase experiments, the secretion of apoE Leiden was comparable to that of both human apoE3 and rat endogenous apoE, approaching 100% in 90 min. In similar transfection experiments, secreted apoE Leiden was significantly less glycosylated than normal apoE3 (21.7% vs. 36.6%, P < 0.005, n = 4), a finding also noted for apoE Leiden in human plasma. In in vitro incubation experiments, apoE Leiden showed a markedly higher preference for VLDL of normolipidemic human plasma when compared to both apoE3 (2.6-fold, P < 0.001) and apoE4 (1.6-fold, P < 0.001). These results suggest that the accumulation of apoE Leiden in VLDL derives from a high affinity of the mutant protein for the VLDL. This enrichment in defective apoE probably exacerbates impairment of VLDL removal from the circulation, thus contributing to the dominant transmission of type III hyperlipoproteinemia