title: Betaine homocysteine methyltransferase is active in the mouse blastocyst and promotes inner cell mass development.
abstract: Methyltransferases are an important group of enzymes with diverse roles that include epigenetic gene regulation. The universal donor of methyl groups for methyltransferases is S-adenosylmethionine (AdoMet), which in most cells is synthesized using methyl groups carried by a derivative of folic acid. Another mechanism for AdoMet synthesis uses betaine as the methyl donor via the enzyme betaine-homocysteine methyltransferase (BHMT, EC 2.1.1.5), but it has been considered to be significant only in liver. Here, we show that mouse preimplantation embryos contain endogenous betaine; Bhmt mRNA is first expressed at the morula stage; BHMT is abundant at the blastocyst stage but not other preimplantation stages, and BHMT activity is similarly detectable in blastocyst homogenates but not those of two-cell or morula stage embryos. Knockdown of BHMT protein levels and reduction of enzyme activity using Bhmt-specific antisense morpholinos or a selective BHMT inhibitor resulted in decreased development of embryos to the blastocyst stage in vitro and a reduction in inner cell mass cell number in blastocysts. The detrimental effects of BHMT knockdown were fully rescued by the immediate methyl-carrying product of BHMT, methionine. A physiological role for betaine and BHMT in blastocyst viability was further indicated by increased fetal resorption following embryo transfer of BHMT knockdown blastocysts versus control. Thus, mouse blastocysts are unusual in being able to generate AdoMet not only by the ubiquitous folate-dependent mechanism but also from betaine metabolized by BHMT, likely a significant pool of methyl groups in blastocysts.
authors: Ottawa Hospital Research Institute, Ottawa, Ontario K1Y4E9, Canada.
authors: Martin B
authors: MB
authors: Lee
authors: Megan
authors: M
authors: Kooistra
authors: Baohua
authors: B
authors: Zhang
authors: Sandy
authors: S
authors: Slow
authors: Amanda L
authors: AL
authors: Fortier
authors: Timothy A
authors: TA
authors: Garrow
authors: Michael
authors: M
authors: Lever
authors: Jacquetta M
authors: JM
authors: Trasler
authors: Jay M
authors: JM
authors: Baltz
mesh_terms: D000818:Animals; D001622:Betaine / Q000378:metabolism*; D050940:Betaine-Homocysteine S-Methyltransferase / Q000235:genetics / Q000378:metabolism*; D001755:Blastocyst / Q000166:cytology / Q000201:enzymology*; D002470:Cell Survival / Q000502:physiology; D047108:Embryonic Development / Q000502:physiology*; D005260:Female; D055785:Gene Knockdown Techniques; D051379:Mice; D009028:Morula / Q000166:cytology / Q000201:enzymology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000235:genetics / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D001622:Betaine; D012436:S-Adenosylmethionine; D050940:Betaine-Homocysteine S-Methyltransferase; C494549:Bhmt protein, mouse