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Conference report: Joint meeting of Rochester Trophoblast Conference and European Placenta Group, Rochester, New York, 9–12 October, 1988
Placenta (I99O), I I, 87~9o
Conference Report: Joint Meeting of Rochester Trophoblast Conference and European Placenta Group, Rochester, New York, 9-i2 October, I988 MAUREEN YOUNG Molecular and Cell Biology o f the P l a c e n t a - - a n d m o r e - - a Physiologist's Point o f View The 1ith Rochester Trophoblast Conference was held, with the European Placenta Group, in Rochester NY, on 9 i2 October, I988. Tribute must first be paid to Richard Miller and his staff for the excellent local organization. The meeting was designated for the 'Molecular Biology and Cell Regulation of the Placenta'--a sign of the times--and the contributions on these subjects provided at least half of the i44 abstracts. The symposium attracted some 274 persons. The meeting started on Sunday morning with a primer course on gene structure and expression given by Robert Angerer of the Biology department at Rochester University. The complexities of the subjects, together with the methods used to elucidate them, were clearly summarized in two I-h sessions. The free communications were divided into eight subsections, which ran consecutively. These included a wide range of subjects in Molecular Biology, Cell Regulation and Trophoblast Transport Mechanisms. The poster demonstrations were put up on the first day and remained in place throughout the meeting, which was a great advantage for viewing. Molecular and Cell Biology The contributions of the molecular and cell biology presentations were various, but the majority were concerned with two topics: firstly, trophoblast:endometrial relationships and, secondly, the molecular expression of the placental hormones; observations on the expression of some growth factors in relation to both topics were included. S. R. Glasser introduced the first topic by discussing the inadequacies of present concepts of blastocyst:endometrial relationships, stressing the importance of obtaining data which would provide a common concept for all types of placentation, distinguishing between the regulation of endometrial preparation and implantation. He advocated the use of new in vitro techniques, with cell:cell observations in primary cultures of polarized uterine epithelial cells, capable of producing hormones. B. J. Cunningham's lecture on 'Cell adhesion molecules (CAMs) in embryonic development' was very relevant to this subject. He described the polypeptide nature of these molecules, with their immunoglobulin-like domains in the binding regions and their expression in very early chick embryo cells. I. Boime started the second topic with a descripion of the well known differences between the time course of appearance of human chorionic gonadotrophin (hCG) and human placental lactogen (hPL) and their relationship to the different structure of the trophoblast, which has o143 4oo4/9o/oioo87+04 $05.00/0
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Placenta 0990), Vol. I i
been demonstrated by in situ hybridization studies. Further observations, using cultured trophoblast, have shown that synthesis of the ~-subunit of hCG precedes that of the fl-subunit and is associated with the mitotically active mononucleate cytotrophoblast; the fl-subunit is only synthesized in newly formed, mitotically inactive multinucleate syncytiotrophoblast. Ectopic placentae produce the ~-subunit, while choriocarcinomas express both subunits but no hPL. Immunology Interest continued in the greatly explored immunological relationship between the mother and fetus; however, the workshop on 'Immunology of the Trophoblast' concluded that no new recent data had been provided in this subject. Tissue Culture The workshop entitled 'Trophoblast differentiation in tissue culture', had a thorough discussion on the methods used to purify and identify trophoblast and concluded that there is still no uniform agreement as to the best approach. T r a n s p o r t and Physiology The papers on placental transport covered a wide field from structural studies to new experimental methods and concepts. B. King, in describing the permeability pathways in the placental membrane, pointed out that the basal lamina did not present such a barrier to large molecules as it did in the glomerulus. Other electron microscope studies revealed the presence of scattered clefts crossing the syncytium of the human placenta, suggesting that placental transport may occur by both intraand extra-cellular pathways (Tedde et al); these workers also have evidence for multinucleate syncytial units within the syncytial layer, linked by cell junctions. A proliferation of the cytoskeleton, to the detriment of other important cell organelles, was observed in toxaemic pregnancy and it was suggested that the nodules formed near the basement membrane interfered with the mobility of the trophoblast, causing a rise in vascular resistance in the fetal placental circulation (Watanabe and Huata). L. Cedard described the receptor mediated endocytosis process for the uptake of low density lipoprotein (LDL) with regard to the large quantity of cholesterol which is necessary for steroid hormone production by the placenta: specific sites, which were saturable, were found on microvilli by 6 weeks of gestation in the human placenta, using ultrastructural localization of ferritin or gold labelled LDL. Transferrin receptors featured in other studies and the vesicles formed by isolated microvilli in further transport investigations. In one, the latter were used to show the part played by the transcellular route in the transport of non-electrolytes; a new method, using fluorescein sulphonate self-quenching, was employed to measure vesicle volume (Illsley). A second new model for placental transport study was described using cultured term trophoblast on amnion basement membrane, so that transfer from either side of the syncytium could be investigated (Bullen and Bloxam). Interestingly, the term trophoblast did not invade the amnion basement membrane, in contrast with the first trimester trophoblast studied by Yagel et al. The rat featured most in the few whole animal studies reported. Large functional changes in the placenta were shown during gestation, by measuring the clearance (Kmf) of labelled molecules of different sizes, using Flexner's original method (I942). Between 15 and 22 days gestation, Km~ increased four- to ninefold for extracellular markers; that for sodium increased 22-fold and 6o-fold was found for calcium. In two studies the fetal placenta was perfused in
Maureen Young: Conference Report
89
situ for bidirectional flux measurements. Net flux values for potassium agreed well with fetal accretion rates (Mohammed et al) and laptake of glucose by the placenta was found to exceed release into the fetal circulation, suggesting some regulation of glucose flux through a placental pool, in addition to 'facilitated diffusion down a concentration gradient' (Thomas and Eriksson). The isolated guinea-pig placenta, dually perfused, was used to study heat transport (Schroder and Hatano). The heat flux efficiency was found to be surprisingly low, accounting for about a quarter of fetal heat production; this was possibly due to intra-placental shunts and to external heat exchange across the placental surface. In the workshop on 'Cellular accumulation v. transplacental movements' active processes with regard to the asymmetric distribution of transporters were discussed (Sibley) and environmental influences on ligand-receptor interaction (Desoye). The latter emphasized the dynamic nature of cell membranes, describing the importance of their fluidity and the enhanced affinity which may be observed, within an hour in vitro, by increasing the concentration of cholesterol or glucose. Lastly, van Dijk talked about the network thermodynamic approach for processing non-steady state data from transport studies, introduced recently by van Kreel. The method was judged to be most valuable in transport studies of pharmacological compounds. Oxygen Supply The oxygen supply to the intact and isolated placenta was still, most appropriately, of concern. This was discussed in the workshop on 'Utero-placental blood flow' with evidence from chronic sheep preparations. There were reports of measurement of the energy status in isolated tissue using 3ip nuclear magnetic resonance spectroscopy (NMR): continuous measurements were made during perfusion of the isolated lobule of the human placenta (Malek et al) and the technique was used in investigations of other reproductive organs; the characteristic spectra were found to change with gestation in the uterus and placenta, but the high energy content of tissues did not alter in disease (Ramam et al). Toxicology Of the papers concerned with toxicology, that relating to the possible influence of ultrasound exposure on the placenta provoked considerable interest; clearance studies in the anaesthetized guinea-pig demonstrated that blood flow might be impaired when beams of high intensity were used (Kelman and Sikov). It was suggested that these results should be considered when the new pulse doppler units for the examination of fetal and umbilical vessels were used.
Postscript Notwithstanding the title, the symposium covered a wide range of interests and expertise, and placental tissue, especially the human trophoblast, cannot now be regarded as neglected by investigators. In the fields of cellular and molecular biology the new activity centred around exploring the trophoblast:endometrial relationships in vitro, is challenging but since there is, as yet, no uniform agreement as to the best approach for trophoblast culture, its use in transport studies must be interpreted with care. The extension of the molecular techniques for localising the expression of hormones and growth factors, particularly the timing of their appearance, will be invaluable to our understanding of the physiology of their functions in the whole animal. Both isolated tissue and whole animal studies also brought out the developmental aspects of the biochemistry and energy status, and of the increases in transfer capacity, of the placenta. The introduction of non-invasive methods, such an nuclear magnetic resonance imaging and
9o
Placenta 0990), Vol. H
spectroscopy is most welcome, and promising, for the exploration of placental and fetal structure and biochemistry. A Korean N M R microscope, giving a resolution of 4 pm, was used to examine the first stages of placentation and embryonic development in gravid rat uteri, excised for the imaging: the results compared well with the same structures examined under the light microscope after fixation (Panigel et al). The future is exciting, for there is already a N M R microscope with the i/lm resolution needed to image cells in vivo.
Conference Report: Joint Meeting of Rochester Trophoblast Conference and European Placenta Group, Rochester, New York, 9-i2 October, I988 MAUREEN YOUNG Molecular and Cell Biology o f the P l a c e n t a - - a n d m o r e - - a Physiologist's Point o f View The 1ith Rochester Trophoblast Conference was held, with the European Placenta Group, in Rochester NY, on 9 i2 October, I988. Tribute must first be paid to Richard Miller and his staff for the excellent local organization. The meeting was designated for the 'Molecular Biology and Cell Regulation of the Placenta'--a sign of the times--and the contributions on these subjects provided at least half of the i44 abstracts. The symposium attracted some 274 persons. The meeting started on Sunday morning with a primer course on gene structure and expression given by Robert Angerer of the Biology department at Rochester University. The complexities of the subjects, together with the methods used to elucidate them, were clearly summarized in two I-h sessions. The free communications were divided into eight subsections, which ran consecutively. These included a wide range of subjects in Molecular Biology, Cell Regulation and Trophoblast Transport Mechanisms. The poster demonstrations were put up on the first day and remained in place throughout the meeting, which was a great advantage for viewing. Molecular and Cell Biology The contributions of the molecular and cell biology presentations were various, but the majority were concerned with two topics: firstly, trophoblast:endometrial relationships and, secondly, the molecular expression of the placental hormones; observations on the expression of some growth factors in relation to both topics were included. S. R. Glasser introduced the first topic by discussing the inadequacies of present concepts of blastocyst:endometrial relationships, stressing the importance of obtaining data which would provide a common concept for all types of placentation, distinguishing between the regulation of endometrial preparation and implantation. He advocated the use of new in vitro techniques, with cell:cell observations in primary cultures of polarized uterine epithelial cells, capable of producing hormones. B. J. Cunningham's lecture on 'Cell adhesion molecules (CAMs) in embryonic development' was very relevant to this subject. He described the polypeptide nature of these molecules, with their immunoglobulin-like domains in the binding regions and their expression in very early chick embryo cells. I. Boime started the second topic with a descripion of the well known differences between the time course of appearance of human chorionic gonadotrophin (hCG) and human placental lactogen (hPL) and their relationship to the different structure of the trophoblast, which has o143 4oo4/9o/oioo87+04 $05.00/0
9 I99oBailli+reTindall Ltd
88
Placenta 0990), Vol. I i
been demonstrated by in situ hybridization studies. Further observations, using cultured trophoblast, have shown that synthesis of the ~-subunit of hCG precedes that of the fl-subunit and is associated with the mitotically active mononucleate cytotrophoblast; the fl-subunit is only synthesized in newly formed, mitotically inactive multinucleate syncytiotrophoblast. Ectopic placentae produce the ~-subunit, while choriocarcinomas express both subunits but no hPL. Immunology Interest continued in the greatly explored immunological relationship between the mother and fetus; however, the workshop on 'Immunology of the Trophoblast' concluded that no new recent data had been provided in this subject. Tissue Culture The workshop entitled 'Trophoblast differentiation in tissue culture', had a thorough discussion on the methods used to purify and identify trophoblast and concluded that there is still no uniform agreement as to the best approach. T r a n s p o r t and Physiology The papers on placental transport covered a wide field from structural studies to new experimental methods and concepts. B. King, in describing the permeability pathways in the placental membrane, pointed out that the basal lamina did not present such a barrier to large molecules as it did in the glomerulus. Other electron microscope studies revealed the presence of scattered clefts crossing the syncytium of the human placenta, suggesting that placental transport may occur by both intraand extra-cellular pathways (Tedde et al); these workers also have evidence for multinucleate syncytial units within the syncytial layer, linked by cell junctions. A proliferation of the cytoskeleton, to the detriment of other important cell organelles, was observed in toxaemic pregnancy and it was suggested that the nodules formed near the basement membrane interfered with the mobility of the trophoblast, causing a rise in vascular resistance in the fetal placental circulation (Watanabe and Huata). L. Cedard described the receptor mediated endocytosis process for the uptake of low density lipoprotein (LDL) with regard to the large quantity of cholesterol which is necessary for steroid hormone production by the placenta: specific sites, which were saturable, were found on microvilli by 6 weeks of gestation in the human placenta, using ultrastructural localization of ferritin or gold labelled LDL. Transferrin receptors featured in other studies and the vesicles formed by isolated microvilli in further transport investigations. In one, the latter were used to show the part played by the transcellular route in the transport of non-electrolytes; a new method, using fluorescein sulphonate self-quenching, was employed to measure vesicle volume (Illsley). A second new model for placental transport study was described using cultured term trophoblast on amnion basement membrane, so that transfer from either side of the syncytium could be investigated (Bullen and Bloxam). Interestingly, the term trophoblast did not invade the amnion basement membrane, in contrast with the first trimester trophoblast studied by Yagel et al. The rat featured most in the few whole animal studies reported. Large functional changes in the placenta were shown during gestation, by measuring the clearance (Kmf) of labelled molecules of different sizes, using Flexner's original method (I942). Between 15 and 22 days gestation, Km~ increased four- to ninefold for extracellular markers; that for sodium increased 22-fold and 6o-fold was found for calcium. In two studies the fetal placenta was perfused in
Maureen Young: Conference Report
89
situ for bidirectional flux measurements. Net flux values for potassium agreed well with fetal accretion rates (Mohammed et al) and laptake of glucose by the placenta was found to exceed release into the fetal circulation, suggesting some regulation of glucose flux through a placental pool, in addition to 'facilitated diffusion down a concentration gradient' (Thomas and Eriksson). The isolated guinea-pig placenta, dually perfused, was used to study heat transport (Schroder and Hatano). The heat flux efficiency was found to be surprisingly low, accounting for about a quarter of fetal heat production; this was possibly due to intra-placental shunts and to external heat exchange across the placental surface. In the workshop on 'Cellular accumulation v. transplacental movements' active processes with regard to the asymmetric distribution of transporters were discussed (Sibley) and environmental influences on ligand-receptor interaction (Desoye). The latter emphasized the dynamic nature of cell membranes, describing the importance of their fluidity and the enhanced affinity which may be observed, within an hour in vitro, by increasing the concentration of cholesterol or glucose. Lastly, van Dijk talked about the network thermodynamic approach for processing non-steady state data from transport studies, introduced recently by van Kreel. The method was judged to be most valuable in transport studies of pharmacological compounds. Oxygen Supply The oxygen supply to the intact and isolated placenta was still, most appropriately, of concern. This was discussed in the workshop on 'Utero-placental blood flow' with evidence from chronic sheep preparations. There were reports of measurement of the energy status in isolated tissue using 3ip nuclear magnetic resonance spectroscopy (NMR): continuous measurements were made during perfusion of the isolated lobule of the human placenta (Malek et al) and the technique was used in investigations of other reproductive organs; the characteristic spectra were found to change with gestation in the uterus and placenta, but the high energy content of tissues did not alter in disease (Ramam et al). Toxicology Of the papers concerned with toxicology, that relating to the possible influence of ultrasound exposure on the placenta provoked considerable interest; clearance studies in the anaesthetized guinea-pig demonstrated that blood flow might be impaired when beams of high intensity were used (Kelman and Sikov). It was suggested that these results should be considered when the new pulse doppler units for the examination of fetal and umbilical vessels were used.
Postscript Notwithstanding the title, the symposium covered a wide range of interests and expertise, and placental tissue, especially the human trophoblast, cannot now be regarded as neglected by investigators. In the fields of cellular and molecular biology the new activity centred around exploring the trophoblast:endometrial relationships in vitro, is challenging but since there is, as yet, no uniform agreement as to the best approach for trophoblast culture, its use in transport studies must be interpreted with care. The extension of the molecular techniques for localising the expression of hormones and growth factors, particularly the timing of their appearance, will be invaluable to our understanding of the physiology of their functions in the whole animal. Both isolated tissue and whole animal studies also brought out the developmental aspects of the biochemistry and energy status, and of the increases in transfer capacity, of the placenta. The introduction of non-invasive methods, such an nuclear magnetic resonance imaging and
9o
Placenta 0990), Vol. H
spectroscopy is most welcome, and promising, for the exploration of placental and fetal structure and biochemistry. A Korean N M R microscope, giving a resolution of 4 pm, was used to examine the first stages of placentation and embryonic development in gravid rat uteri, excised for the imaging: the results compared well with the same structures examined under the light microscope after fixation (Panigel et al). The future is exciting, for there is already a N M R microscope with the i/lm resolution needed to image cells in vivo.