Journal of Animal Science

SCHUETZ, ALLEN, W.

doi: 10.1093/ansci/49.Supplement_II.1pmid: 400775

Summary THE relationship between gametogenesis and conceptus development has been described in relation to recent experiments concerning selected aspects of the cellular and molecular basis of differentiation of female and male gametes. Evidence suggests that a variety of hormonal and nonhormonal mechanisms or combinations thereof have evolved and control distinct stages of oocyte maturation process. Analyses of the meiotic maturation process with particular emphasis on amphibians, indicate that distinct cytoplasmic factors are produced or activated in response to a hormonal stimulus which initiates germinal vesicle breakdown and reinitiates the meiotic maturation process. Evidence suggests that certain cytoplasmic factors originate in the nucleus and (or) cytoplasm and that considerable cytoplasmic maturation proceeds in the absence of the nucleus, or as a result of nuclear-cytoplasmic interactions. Cytoplasmic factor(s) or activities affect many aspects of oocyte function and structure, including the cell membrane, chromosomes, nucleus and meiotic spindle. Ions also play a crucial role in gamete differentiation either alone or in combination with hormones or these cytoplasmic factors. The relevance of these findings to oocyte maturation and fertilization, activation and embryonic development is discussed. In many cases, similar types of biological activities exist in widely separated species and (or) are effective in widely different species. The importance of synchronization of normal gametes to the development of the embryos is discussed. It is proposed, and the evidence suggests, that hormones, ions and cytoplasmic factors play a fundamental and variable role in the differentiation and function of “fully” mature oocytes of many species including mammals. Significantly, the data suggest that a “fully” mature oocyte occurs as a result of the expression of an underlying developmental program. Variations in these substances or the processes involved in their formation or actions appear to be relevant to understanding a wide variety of developmental abnormalities as well as to assessing the normality or abnormality of in vivo or in vitro maturation and differentiation. This content is only available as a PDF. Author notes 2 Department of Population Dynamics. 1979 by American Society of Animal Science

BRINSTER, R., L.;TROIKE, D., E.

doi: 10.1093/ansci/49.Supplement_II.26pmid: 45481

Summary FOUR characteristics of culture medium that are important to embryo development and nutrition of the blastocyst have been discussed. An examination of several of the most commonly used media for embryo culture demonstrates many similarities among them. The milliosmolarities of the media range from the hypoosmotic optimums (256 milliosmols) demonstrated in several in vitro studies to the physiologic range (308 to 315 milliosmols). Media between these extremes generally allow good development. Low oxygen concentrations (5%) in the culture environment allow somewhat better development of early cleavage stages, but recent studies suggest the difference between development in 5 and 20% oxygen to be less than originally thought. The media most commonly employed for early embryo culture contain bicarbonate as the buffer, but maintenance of pH is probably not the most crucial role of the CO2-bicarbonate content of the media. Likewise, since 1965 almost all media used to culture embryos have used pyruvate as the primary energy source. This is particularly important when early stages, before blastocyst development, are cultured. The concentration used generally falls within the optimum range of 2.5 to 5.0 × 10−4 M first reported. Although glucose is not oxidized well by the early cleavage stages, it is an important energy source for all blastocysts. Furthermore, glucose contributes more than any other carbon source, including amino acids, to protein formation. Much is yet to be learned concerning the nutrition of the blastocyst, but our knowledge has increased immensely during the last 15 years. Hopefully our progress will be at least as rapid in the coming decade. This content is only available as a PDF. Author notes 1 Financial support for the authors’ research has been from the National Institute of Child Health and Human Development (HD 12384, HD 08539), The National Cancer Institute (CA 14676) and the Population Council. D. E. Troike was a trainee on NICHHD grant HD 00239. 2 We thank Eleanor Lang for assistance in preparation of this manuscript. 4 Laboratory of Reproductive Physiology. 1979 by American Society of Animal Science

BAZER, FULLER, W.;ROBERTS, R., MICHAEL;THATCHER, WILLIAM, W.

doi: 10.1093/ansci/49.Supplement_II.35pmid: 400776

Summary THE process of reproduction in the mammalian female involves interactions between gonadal and placental steroids and, possibly, protein hormones such as placental lactogen, and the uterine endometrium. These interactions are discussed relative to available data from pigs and with the understanding that the concepts presented may not be directly applicable to other species. Swine embryos enter the uterus for continued development beyond the early blastocyst stage and, within the uterus, the spherical blastocyst, of about 2 mm diameter on day 12, undergoes rapid elongation to an organism of about 1 m in length by day 15 of pregnancy. During this period of elongation, the blastocyst appears to provide the chemical signal, presumably unconjugated estrogens, that allows for corpora lutea (CL) maintenance (luteostatic effect) and, therefore, continued production of progesterone by the CL which is essential for pregnancy. Estrogens from the blastocyst may exert their luteostatic effect on the uterus by causing prostaglandin F2α, the presumed porcine uterine luteolysin, to be secreted in an exocrine (toward the uterine lumen) rather than an endocrine (toward the endometrial stroma and vasculature) direction during pregnancy. Consequently, prostaglandin F2α is sequestered in the uterine lumen and does not become available, via the utero-ovarian vasculature, to exert its luteolytic effect. The potential steroid precursor(s) available to the trophoblast for estrogen synthesis appear to be produced through endometrial conversion of progesterone to unconjugated androgens, e.g., androstenedione and testosterone, and conjugated estrogens, e.g., estrone-sulfate and estradiol-sulfate. The estrogens may, in concert with progesterone and possibly other hormones, placental lactogen for example, act locally, i.e., at the site of placentation to: (1) result in a luteostatic effect; (2) increase uterine blood flow; (3) enhance water, electrolyte and substrate (carbohydrate and amino acid) transport to the site of placentation and across the placenta; (4) affect synthesis and secretion of macro-molecules (histotroph) by the uterine glands that serve as enzymes and (or) carrier molecules and (5) control or modulate physiological and (or) biochemical events essential to placental and fetal development that are not understood. This content is only available as a PDF. Author notes 2 Department of Animal Science. 3 Department of Biochemistry. 4 Department of Dairy Science. 1979 by American Society of Animal Science

CLARK, J., H.;HARDIN, J., W.;McCORMACK, S., A.

doi: 10.1093/ansci/49.Supplement_II.46pmid: 400777

Summary THE relationship between estrogen agonists and antagonists and the nuclear binding of the estrogen receptor was investigated in the immature rat uterus. Estriol (and other short acting estrogens) are antagonistic when administered as a single injection due to the inability of the receptor-estriol complex to be retained by uterine nuclei for a critical period necessary to stimulate true uterine growth. This failure of the receptor-estriol complex to be retained appears to be due to rapid clearance of estriol from uterine tissue following a single injection of the hormone. When estriol is present in a chronic fashion, it acts as an agonist because receptor estriol complex is retained at nuclear sites for long periods of time. Nonsteroid estrogen antagonists, such as Nafoxidine, also cause long term nuclear retention of the estrogen receptor and act as estrogen agonists after a single injection. However, after multiple injections these drugs are antagonistic and this effect is correlated with decrease availability of cytoplasmic estrogen receptors. In addition, these compounds appear to specifically stimulate the growth of uterine epithelial cells while minimally affecting other cell types which results in hyperestrogenization of the epithelium. This content is only available as a PDF. Author notes 1 Department of Cell Biology. 1979 by American Society of Animal Science

BRADFORD, G., E.

doi: 10.1093/ansci/49.Supplement_II.66pmid: 400778

Summary THE nature of genetic variation in litter size and its components was examined using results of long term selection and of crossing selected lines of mice. Selection for small and for large litters produced strains with mean litter size of approximately 6 and 15, respectively. The large litter size line showed a period of renewed response after 45 generations of selection, following a period of 15 generations with no response. The relative contribution of genotype of the dam and of the embryo to prenatal survival was examined using results of selection, crossing and embryo transfer. Genotype of female carrying the litter was responsible for most of the observed differences. Genes for poor survival expressed by the embryo were present in some strains, but accounted for less variation than did maternal genotype. Information from the selected lines and from crosses among them provided evidence for dominance of genes affecting fertility and prenatal survival and additivity of genes affecting ovulation rate and body weight. The information was used to suggest a model for more effective exploitation of heterosis using breeds or strains of animals of known performance for different components. The extent of genetic variation for prenatal survival suggests that natural selection in this species may not always be for maximum survival. It is suggested that the ability to reduce litter size after conception, in response to nutritional or other stress, may at times be of selective advantage, contributing to maintenance of genetic variation in survival rate. This content is only available as a PDF. Author notes 1 The author expresses his sincere appreciation to Gary Anderson, Terry Moler, Roberto Neira, Sandra Soga and Jimmy Spearow for their contributions to the results included in this paper. The animal colony was under the able supervision of Oskar Lang. 3 Department of Animal Science. 1979 by American Society of Animal Science