Quantitative changes in cytoskeletal beta- and gamma-actin mRNAs and apparent absence of sarcomeric actin gene transcripts in early mouse embryos.
Actin is known to be synthesized both during oogenesis and in cleavage-stage embryos in mice. Cytoskeletal beta-actin appears to be the major component, followed by gamma-actin, but the synthesis of alpha-actin has also been inferred from protein electrophoretic patterns. We have studied the expression of cytoskeletal (beta- and gamma-) and sarcomeric (alpha-cardiac and alpha-skeletal) actin genes at the level of the individual mRNAs in blot hybridization experiments using isoform-specific RNA probes. The results show that there are about 2 x 10(4) beta-actin mRNA molecules in the fully grown oocyte; this number drops to about one-half in the egg and less than one-tenth in the late two-cell embryo but increases rapidly during cleavage to about 3 x 10(5) molecules in the late blastocyst. The amount of gamma-actin mRNA is similar to that of beta-actin in oocytes and eggs but only about 40% as much in late blastocysts, indicating a differential accumulation of these mRNAs during cleavage. The developmental pattern of beta- and gamma-actin mRNA provides a striking example of the transition from maternal to embryonic control that occurs at the two-cell stage and involves the elimination of most or all of the maternal actin mRNA. There was no detectable alpha-cardiac or alpha-skeletal mRNA (i.e., less than 1,000 molecules per embryo) at any stage from oocyte to late blastocyst, suggesting that the sarcomeric actin genes are silent during preimplantation development.
Taylor
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KD
Developmental Biology Laboratory, VA Medical Center, Sepulveda, California 91343.
Pikó
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L
D000199:Actins / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D001755:Blastocyst / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism*; D004247:DNA / Q000032:analysis; D004622:Embryo, Mammalian / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009210:Myofibrils / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D012518:Sarcomeres / Q000378:metabolism*; D014158:Transcription, Genetic
D000199:Actins; D012333:RNA, Messenger; D004247:DNA