Printed in Sweden Copyright @ 1978 by Academic Press, Inc. All rights of reproduction in any form reserved 00144827/78/1141-0135$02.00/O Experimental Cell Research 114 (1978) 135-141 SYNTHESIS OF TUBULIN AND ACTIN DURING THE PREIMPLANTATION DEVELOPMENT OF THE MOUSE SERGIO L. ABREU’,* and RALPH L. BRINSTER University of Pennsylvania, School of Veterinary Medicine, Laboratory of Reproductive Physiology, Philadelphia, PA 19103, USA SUMMARY The relative rates of synthesis of actin and tubulin during mouse preimplantation development have been investigated utilizing O’Farrell’s two-dimensional polyacrylamide gel system and inter- nal protein markers. During mouse preimplantation development, rates of protein synthesis remain low and are little changed until the 8-cell stage when a rapid increase is evident. From the &cell stage on, a much higher rate of synthesis is maintained. The rate of synthesis of actin remains also at a steady low level in the unfertilized and fertilized ovum. However, by the g-cell stage actin synthesis has increased IO-fold. Our measurements include the blastocyst, at that point in devel- opment actin synthetic rates are almost 90-fold higher than in the unfertilized ovum. While this precipitous increase is proceeding, incorporation of [3H]leucine into total protein increases only 7-fold. Synthesis of actin in the blastocyst represents 5.7% of total protein synthesis. The rate of tubulin synthesis, unlike actin, more closely parallels the increments in total protein synthetic rates. At the blastocyst stage it has increased 14-fold and its synthesis represents almost 2% of total protein synthesis. These results are discussed with reference to some of the physiological changes taking place during preimplantation development. During preimplantation development, the protein content of the mouse embryo does not exceed 30 ng [l]. In spite of this pau- city of experimental material, a great deal of progress has been made in the study of protein synthesis during this developmental period. Since the initial studies showing that the mouse preimplantation embryo incorpo- rates amino acids into proteins [2-4], a number of increasingly sophisticated inves- tigations have been performed. Embryonic protein synthesis has been shown to be re- quired for preimplantation development [e.g. 5, 61 and the uptake of several amino acids has been studied [7-91. Major changes in the qualitative pattern of protein synthe- sis have been shown to take place at dif- ferent stages of development [ 10, 111. And changes in a variety of enzyme activities during development have been determined [see [12] for a review]. Recently, the intra- cellular specific activity of leucine during mouse preimplantation development has been measured [ 131,allowing for the calcu- lation of the intracellular leucine pool size and the absolute rate of protein synthesis [131- With the exception of a recent commu- nication on the synthesis of lactic dehydro- genase-1 [ 141, no studies on the relative synthesis of individual proteins have been reported. We feel that such studies are of ’ Present address: Sloan-Kettering Institute for Can- cer Research, Section 6144, 1275 York Avenue, New York, NY 10021, USA. 2 To whom reprint requests should be addressed. Exp Cell Res 114 (I 978)