Uptake of betaine into mouse cumulus-oocyte complexes via the SLC7A6 isoform of y+L transporter.

Betaine (N,N,N-trimethylglycine) has previously been shown to function in cell volume homeostasis in early mouse embryos and also to be a key donor to the methyl pool in the blastocyst. A betaine transporter (SLC6A20A or SIT1) has been shown to be activated after fertilization, but there is no saturable betaine uptake in mouse oocytes or eggs. Unexpectedly, the same high level of betaine is present in mature metaphase II (MII) eggs as is found in one-cell embryos despite the lack of transport in oocytes or eggs.

Measuring transport and accumulation of radiolabeled substrates in oocytes and embryos.

Radiolabeled compounds that are substrates for transmembrane transporters can be used to study transport and metabolism in mammalian oocytes and preimplantation embryos. Because even very small amounts of radioisotopes can be detected, these techniques are feasible to use with only a few oocytes or embryos, even down to the level of single oocytes or embryos. Here, we describe the methods for determining the transport and accumulation of radiolabeled compounds into oocytes and preimplantation embryos and the determination of the rate of saturable transport via specific transporters in the plasma membrane.

Amino Acid transport mechanisms in mouse oocytes during growth and meiotic maturation.

Amino acids are transported into cells by a number of different transport systems, each with their own specific range of substrates. The amino acid transport systems active in preimplantation embryos and the amino acids required by embryos for optimal development have been extensively investigated. Much less is known about amino acid transport systems active in growing and meiotically maturing oocytes or about developmental changes in their activity.