PARENT SESSION
PLATFORM SESSION 3: EMBRYO METABOLISM, DIFFERENTIATION, AND PROGRAMMED CELL DEATH
Chair: Wolf, Don¹, ¹
Co-chair: Livingston, Tracy¹, ¹
Grand Ballroom I-IV
4:30 PM-6:30 PM

(16) BETAINE IS TRANSPORTED INTO 1-CELL MOUSE EMBRYOS VIA A NOVEL TRANSPORT MECHANISM AND FUNCTIONS AS AN ORGANIC OSMOLYTE.

Baltz, Jay^1,2, Hammer, Mary-Anne¹, ¹ Ottawa Health Research Institute, Ottawa, CA² Depts of Ob/Gyn and Cellular & Molecular Medicine, Ottawa, CA

ABSTRACT- It has become clear in recent years that early preimplantation (PI) mammalian embryos accumulate organic compounds as intracellular osmolytes. Fertilized mouse eggs only develop through the PI stages in vitro at osmolarities similar to those of oviductal fluid if organic osmolytes are available. Specific transporters for organic osmolytes mediate their osmosensitive accumulation. One of the most effective compounds for protecting mouse embryos against increased osmolarity is betaine (N,N,N-trimethylglycine). We have now shown that betaine accumulation in 1-cell mouse embryos increases significantly with increased osmolarity, confirming its role as an organic osmolyte in embryos. Glycine is also highly effective for osmoprotection of embryos and its accumulation is also regulated by osmolarity, and thus we initially hypothesized that betaine was transported via the glycine transporter in embryos, GLY. However, we have now found that the transport of glycine is not inhibited by a large excess of betaine, nor is betaine transport inhibited by excess glycine, indicating that betaine transport is via a separate mechanism. Betaine transport is entirely Na⁺ and Cl^--dependent in 1-cell mouse embryos, indicating that the transport mechanism may be related to GLY and the renal Betaine/GABA transporter (BGT1). Excess GABA, however, did not affect betaine transport, nor did the BGT1 inhibitor phloretin, indicating that the betaine transporter in embryos is distinct. We have found, however, that betaine transport in mouse embryos is strongly inhibited by excess proline, indicating that the organic osmolyte transporter in embryos may be a proline transporter as well as a betaine transporter. These properties are different from those of known mammalian organic osmolyte transporters, and thus the embryonic betaine transporter may be a novel mammalian organic osmolyte transporter, or indicate a novel function in embryos for a proline transporter such as the IMINO system of intestine. (Funded by a University of Ottawa URF grant, and Canadian Institutes of Health Research grant MOP12040)

KEY WORDS: preimplantation embryo, osmolyte, betaine, transport