F. B. P. Wooding

The synepitheliochorial placenta of ruminants: Binucleate cell fusions and hormone production

Grosser’s classification of placentas by the number and form of the layers intervening between the fetal and maternal circulations is generally considered the most useful and instructive yet devised (Amoroso, 1952; Steven, 1975). However, it needs to be recognized as a purely anatomical categorization with no necessary corresponding physiological efficiencies nor evolutionary predictions. It is therefore as important to incorporate new anatomical evidence to update the scheme as it is to consider the possible functional relevance of the differences. Previous suggested extensions to the scheme such as hemoendothelial (Owers, 1960) or endothehoendothelial (Mossman, 1937) placentation have been shown by electron microscopic investigation to be invalid because a continuous fetal endothelium and chorion always persist albeit very thinly in places. However, recent electron microscope and other work has demonstrated that the syndesmochorial category needs re-assessment. The ruminant placenta was defined as syndesmochorial because Grosser considered that the uterine epithelium disappeared and the fetal trophectoderm was apposed directly to the maternal connective tissue (Borlands Medical Dictionary, syndesmo = related to connective tissue). Subsequent workers demonstrated that the uterine epithelium persisted (sometimes in a syncytial form) and therefore reclassified the ruminant placenta as epitheliochorial (Ludwig, 1962; Steven, 1975, 1983; Ramsey, 1982). In the last decade evidence has accumulated to show that a unique feature of the ruminant placenta is the population of fetal chorionic binucleate cells (BNC) which migrate throughout pregnancy through the chorionic tight junction to fuse with uterine epithelial cells or their derivatives [Figures l(a) and (b)]. The horse placenta produces migratory binucleate cells (Allen, Hamilton and Moor, 1973) but these are transient and never fuse with maternal cells. Ruminant BNC are directly involved in the modification of the uterine epithelium, beginning at implantation and continuing until term (Wooding, 1982, 1983; Wooding et al, 1986). The uterine epithelium persists but is modified to a variable degree, depending on species, into a hybrid fetomaternal syncytium formed by the migration and fusion of the fetal binucleate cells with those of the uterine epithelium. The mature ruminant placenta is neither entirely syndesmochorial with no uterine epithelium, nor epitheliochorial with two apposed cell layers whose only anatomical interaction is interdigitated microvilli. Thus in sheep and goats all the placentoma1 membrane, more than 95 per cent of the total (placentomal plus interplacentomal) in the second half of pregnancy, form a fetomaternal syncytium at the fetomatemal interface IFigure l(b); Wooding, 1984; Wango et al, 1990a,b]. In cow and deer, although at

Identification, properties, and differential counts of cell populations using electron microscopy of dry cows secretions, colostrum and milk from normal cows.

Differential counts of electron microscope sections of cell pellets isolated from bovine udder secretions showed that no secretory epithelial cells and very few ductal epithelial cells were present at any stage. The predominant cell type was the macrophage in dry and lactating cows or the polymorphonuclear leucocyte (PMNL) in colostrum. Lymphocytes were also present but no plasma cells were found. The macrophages took up polystyrene latex particles (as did the PMNL) and adhered to glass in culture. Neither macrophage- nor PMNL-rich cell suspensions produced any increase in free fatty acid levels when incubated with fresh milk.

The structure of the milk fat globule membrane.

The nature of the milk fat globule membrane (MFGM) is shown to depend upon the length of time since the globule was secreted. The initial MFGM consists of a plasmalemma and cytoplasmic material and is present only immediately after release from the secretory cell. Most of the initial MFGM is lost into the milk plasma by a process of vesiculation, leaving a structureless secondary MFGM as the only continuous boundary to the milk fat globule. The relevance of this process to the biochemical studies on the MFGM is briefly discussed.

Functional specialization in the ruminant placenta : Evidence for two populations of fetal binucleate cells of different selective synthetic capacity

Trophoblast binucleate cells (BNC) in the ruminant placenta demonstrate a characteristic development, mature structure and migratory capacity whether situated in cotyledonary or intercotyledonary regions of the placenta. However, previous immunocytochemical studies demonstrated clear differences in gene expression in granule contents of BNC according to their anatomical location with some proteins being expressed in all BNC (e.g. ovine placental lactogen) whereas others were unique to a particular origin (e.g. SBU3 antigen in cotyledonary BNC only). We have used enriched preparations of binucleate cells and showed differences in steroid metabolic capacity in vitro which is more related to their species origin (sheep or goat) than to their anatomical location. The predominant product from [3H]pregnenolone is progesterone (sheep) and 5 beta-pregnane-3 alpha, 20 alpha-diol (goat) and the amount formed (corrected for the number of BNC) is similar irrespective of whether BNC were derived from the cotyledonary or intercotyledonary regions. These studies indicate specific forms of regional functional specialization of BNC and emphasize their multifunctional role in the ruminant placenta.

The fine structure of the mature resin canal cells of Pinus pinea.

The ultrastructural features of the resin canal cells of Pinus pinea are described. These include numerous plastids closely sheathed with endoplasmic reticulum. This sheath endoplasmic reticulum is continuous with the nuclear membrane and peripheral aggregates of endoplasmic reticulum. Small lipid vesicles can be seen in association with these aggregates of endoplasmic reticulum and also on both sides of the plasmalemma. Possible functions of the endoplasmic reticulum association with the plastids are discussed, together with the origin of the duct material.

Trinucleate cells and the ultrastructural localisation of bovine placental lactogen

SummaryBovine placental lactogen activity is shown by immunogold electron microscopy to be restricted to (a) the granules and the Golgi body from which they form in the bovine fetal trophectodermal binucleate cell, and (b) granules of similar size and staining reaction in trinucleate “giant” cells found in the maternal uterine epithelium throughout pregnancy. These results support the hypothesis that a fetal binucleate cell forms a maternal giant cell by migration to and fusion with a uterine epithelial cell.

Calcium transport and the localisation of calbindin-D9k in the ruminant placenta during the second half of pregnancy

Abstract.In late pregnancy the sheep fetus requires 3 g of calcium per day, all of which must be transported across the trophoblast epithelium of the placenta. Such high levels of calcium transport across other epithelia are normally associated with the presence of calbindin-D9 or -28k. Our immunocytochemical results show that ovine, bovine and caprine interplacentomal trophoblast have high levels of calbindin-D9k, about eight to ten times more than in the placentomal region. The protein is detectable only in the uninucleate trophoblast cells in sheep and goat, the frequent binucleate cells show none. The calbindin-D9k is also present in the maternal glandular epithelium but not the surface epithelium of the uterus. The cellular distribution of the calbindin-D9k immunoreactivity suggests a soluble protein homogenously distributed through cytosol and nucleoplasm but absent from all organelles and intercellular spaces. In contrast, the uterine milk protein(s) are localised in Golgi cisternae and secretory vesicles in gland cells and in apical small endocytic vesicles and lysosomes in the uninucleate trophectodermal cells. The distribution of calbindin-D9k supports the concept that it mediates the high calcium flux by facilitated diffusion and not via any vesicular, membrane-bounded system.

The effect of Triton X-100 on the ultrastructure of ejaculated bovine sperm

Ejaculated bull sperm incubated in 0.1% Triton show a rapid and reproducible sequence of membrane losses demonstrating differential stability in areas of continuous membrane. Concurrent changes in density of the acrosomal content indicate that there is a definite structure underlying the homogeneous appearance of the intact acrosome. These changes are compared with the changes reported for sperm of other species during the fertilization process.

Placentation in the African elephant (Loxodonta africana): II morphological changes in the uterus and placenta throughout gestation.

The gross and microscopic development of the zonary endotheliochorial placenta in the African elephant was studied in 22 gravid uteri that ranged in gestational stage from 0.5 to 20.6 months. The conceptus only ever occupies one horn of the uterus and is associated with 2-5 large corpora lutea that persist in the ipsilateral ovary throughout gestation. Initially, the trophoblast in the equatorial region of the conceptus completely replaces the lumenal epithelium of the endometrium to which it is apposed. Blunt upgrowths of endometrial stroma then develop, each closely invested by trophoblast, and containing the capillaries that will vascularize this maternal component of the resulting placental band. With advancing gestation the lamellate stromal upgrowths increase markedly in length and become much thinner, thereby bringing the trophoblast into intimate contact with the endothelium of the maternal capillaries. They also become folded or pleated to increase the total area of intimate feto-maternal contact. At the lateral edges of the placental band the lamellae bend over towards the endometrium to form a blind cleft. Leakage of blood into this area creates haemophagous zones in which phenotypically specialized trophoblast cells phagocytose the blood components. The presence of large resorbing blood clots and circumferential scars in the uteri of three post parturient animals initiated the hypothesis that, when the standing elephant gives birth at term, the passage of the 120 kg fetus through the vagina may wrench the placenta off the endometrium by severing its very narrow maternal placental hilus. The resulting intrauterine haemorrhage may then play a role in preventing further conception for around 2 years.

Ultrastructural localisation of oxytocin and neurophysin in the ovine corpus luteum

SummaryPolyclonal rabbit antisera raised against oxytocin, bovine neurophysin I and vasopressin were used, together with an immunogold complex, to localise the peptides in ultrathin sections of ovine corpus luteum. The only organelle which consistently showed gold labelling was the secretory granule of the large luteal cell. In non-consecutive sections of the same large luteal cell all the granules showed a similar level of labelling after oxytocin or neurophysin I antisera: however no immunolabelling was detected for vasopressin. Oxytocin and neurophysin seem to be rapidly lost after secretion since exocytosed granule cores showed no labelling above background levels.