We have cloned and sequenced a cDNA coding for rice elongation factor 1B (EF-Ifi). The clone was 1420 bp long and contained an open reading frame coding for 229 amino acids. The overall identity between rice EF-lp and rice EF-IF [Matsumoto, S., Oizumi, N., Taira, H. and Ejiri, S. (1992) FEBS Lett. 3 11, 46481 is 60% at the amino acid sequence level; a higher percent identical residues (8 1%) were especially observed in the C-terminal region. Rice EF-l/7 has no conserved phosphorylation site for casein kinase II and no leucine zipper motif, although these motifs are well conserved m EF-16 (=/I in plants) subunits of animal EF-1.

Abstract. The embryonic development and changes of the uterine tissue during pregnancy were examined morphologically to reveal causes of the age-related decline in litter size in the golden hamster. Uteri were obtained from young (9-12-week old, n=48) and aged hamsters (43-53-week old, n=47) at estrus and on Days 2 to 16 of pregnancy. Viability of conceptuses were examined in half of implants from Day 6 onwards by a dissecting microscope. The remaining implants were evaluated histologically. The number of resorbing implants was significantly larger in the aged hamsters than in the young females on Day 6 (4.4 vs. 1.2, p<0.05), although no difference was found in the overall mean number of ova ovulated (14.8 vs. 14.2, respectively). Delays in the embryonic development and uterine response were observed in all aged hamsters throughout gestation. Resorbing implants noted in the aged hamsters were accompanied with stunted decidual cells having pale cytoplasm (incomplete decidualization) and heavy infiltration of endometrial granulocytes. It is suggested that the embryonic wastage may occur much crucially during the peri-implantaion period rather than late gestational period, due to the retarded development of embryos and lessdeveloped decidualization, and that endometrial granulocytes may function in resorption of greatly retarded embryos in the aged hamsters.

Abstract. Uterine luminal surface of the hamster was examined by scanning electron microscopy (SEM) to determine whether aging alters surface ultrastructure of the endometrium where implantation takes place. On Days 2 to 3, the epithelial cells of young hamsters were round and uniformly covered with microvilli. The cells of aged hamsters were polygonal in shape with microvilli of equal density. However, in about 15% of the aged uterine epithelium examined the cells had a reduced number of microvilli. The cellular protrusions appeared on the apical membrane in young uteri on Day 4, but fewer protrusions were observed in aged uteri on Day 5 and some of them were lost before implantation. Implantation was delayed in the aged females. These findings suggest that altered surface ultrastructure of the aged uterus may reflect age-related implantation failure.

Development and enzyme activities of embryos during the preimplantation period were examined to reveal causes of the age-related embryonic loss in the golden hamster. Embryos were obtained from young (9-12-week old, n=40) and aged hamsters (43-53-week old, n=40) on Days 2, 2.5, 3 and 3.5 of pregnancy and the number and developmental stages were recorded. In order to compare the viability of the embryos, the metabolic activities of mitochondria, microsomes, plasma membrane and lysosomes were examined histochemically. Early embryos from aged hamsters showed delays in their development and transport through the oviduct compared to those from young females. The embryos exhibiting strong activities of succinate dehydrogenase, isocitrate dehydrogenase and ∆ 5-3β-hydroxysteroid dehydrogenase were significantly diminished in the aged females. The present results suggest that the reduced metabolic activity may be one possible reason for the retarded development of embryos and that the asynchronous development and delayed migration of the embryos into the uterus may partly account for the embryo loss in the aged hamsters.

Abstract. The protein compositions of uterine secretions in young and aged hamsters during early pregnancy were studied by polyacrylamide slab-gel electrophoresis. Uterine luminal fluids were collected by flushing with a small amount of saline. A broad area of very rapidly migrating proteins, which was undetectable in plasma samples, appeared in the uterine fluids on Days 4 and 5 of pregnancy, which is when implantation occurs in this species. More protein bands were noted in this region in aged females in contrast to those of young females. Further, in the uterine fluids of aged hamsters, a post-albumin protein band disappeared at estrus and on Day 1 and the protein compositions in the post-transferrin region differed between the young and aged females. The qualitative changes in the protein content of the uterine fluids may account for the high rate of embryonic loss in aged hamsters.