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Changes in the distribution of fibronectin in the placenta during normal human pregnancy
Rabbit whole-body versus uterine oxygen extraction
Volume 152 Number 6. Part I
8. Dhindsa DS, Hovensland AS, Metcalfe J. Resting hemodynamic and oxygen transport in unanesthetized adult cats. Respir Physiol 1979;38 : 105. 9. Korner PI, Smith D. Cardiac output in normal unanaesthetized and anaesthetized rabbits. Aust J Exp Bioi Med Sci 1954;32 :499. 10. Duncan S, Lewis B. Maternal placental and myometrial blood flow in the pregnant rabbit.J PhysioI1969;202 :47 1. I I . Meschia G. Circulation to female reproductive organs. In : Handbook of Physiology-The ca rdiovascular system I II . Bethesda: American Phsyiological Society, 1983:24 1. 12. Rosenfeld CR. Distribution of cardiac output in ovine pregnancy. AmJ Physiol 1977;232: H23J. 13. Myers SA, SparksJW, Makowski EL, Meschia G, Battaglia
14. IS . 16. 17.
FC. Relationship between placental blood flow and placental fetal size in guinea pig. Am J Physiol 1982; 243:H404. Moll W, Kastendieck E. Transfer of N2 0, CO and HTO in the artificially perfused guinea pig placenta. Respir Physiol 1977;29:283. Wilkening RB, Anderson S, Martensson L, Meschia G. Placental transfer as a function of uterine blood flow. Am J Physiol 1982;242( 11):H429-36. Block SM,Johnson RL, SparksJW, Battaglia Fe. Uterine metabolism of the pregnant guinea pig as a function of gestational age (in preparation). Rosner B. Fundamentals of biostatistics. Boston: Duxbury Press, 1982.
Changes in the distribution of fibronectin in the placenta during normal human pregnancy Yu Yamaguchi, M.D., Mamoru Isemura, Ph.D., Zensaku Yosizawa, Ph.D., Kosei Kurosawa, M.D., Kaoru Yoshinaga, M.D., Akira Sato, M.D., and Masakuni Suzuki, M.D. Sendai, Japan The distribution of fibronectin, a major extracellular glycoprotein with various activities that affect the proliferation and differentiation of cells, was studied by immunofluorescence staining in first-, second- and third-trimester placentas from normal human pregnancy. In early chorionic villi, fibronectin was localized mainly in the trophoblastic basement membranes; this fluorescence became weaker after 10 weeks' gestation. In term placenta, fibronectin was densely deposited around the fetal vessels but not in the trophoblastic basement membranes. Both syncytiotrophoblasts and cytotrophoblasts of the villous epithelium were virtually negative throughout pregnancy. However, the pericellular matrices of nonvillous trophoblasts in early chorionic villi were strongly stained. These findings suggest that fibronectin plays an important role in the proliferation of trophoblastic cells and the tissue organization of the placenta. (AM J OesTET GYNECOL 1985;152:715-8.)
Key words: Fibronectin, human placenta, trophoblast, basement membrane, immunofluorescence, developmental change Fibronectin is a high molecular weight glycoprotein with a variety of biologic activities, including cell adhesion, embryonic cell migration, wound healing, and differentiation of cells." 2 It is present in soluble form in plasma and amniotic fluid, and in insoluble form in extracellular matrix. The extract of human term placenta has been shown to contain a protein antigenically indistinguishable from plasma fibronectin/ and, recently, Zhu et aI.' and we; have reported the isolation
and biochemical characterization of human placental fibronectin. The present study was designed to show the distribution of fibronectin in the placenta during normal human pregnancy by indirect immunofluorescence staining. We report here that the distribution of fibronectin changes during the development of chorionic villi.
From the Departments of Obstetrics and Gynecology, Medicine, and Biochemistry, Tohoku University School of Medicine. Supported in part by a grant-in-aid for scientific research from the Ministry of Education, Science and Culture of japan. Received for publication October 25, 1984; revised February 21, 1985; accepted February 25, 1985. Reprint requests: Dr. Yu Yamaguchi, Department of Obstetrics and Gynecology, Tohoku University School of Medicine, Sendai 980, japan.
Placenta. Human trophoblastic tissues were obtained from pregnancies terminated in the first and second trimesters by legal abortion and from normal pregnancies at term immediately after delivery. In the case of term placentas, portions of the central cotyledon were selectively dissected and used for staining. All tissues were examined histologically to assure normal
Material and methods
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Yamaguchi et al.
Fig. 1. Chorionic villi of (A) 4 weeks' and (B) 7 weeks' gestation stained by immunofluorescence technique with anti-fibronectin antibodies. Note linear, continuous pattern of fluorescence along the trophoblastic basement membranes. (A, x 90; B, x 180.)
morphologic features before being immunohistochemically stained. The numbers of placentas studied were 10, 5, and lO for first, second, and third trimesters, respectively. Preparation of fibronectin. Human plasma fibronectin was obtained in a pure form from adult human plasma, as described previously.· Human placental fibronectin was isolated according to the method described previously.5 Preparation of antibodies. Anti-human fibronectin antibodies were prepared by immunizing rabbits with plasma fibronectin and absorbed with fibronectin-depleted human plasma which had been coupled to Sepharose 4B, as described previously.· The antibodies were shown to produce a single precipitin arc when reacted with human plasma by immunoelectrophoresis." Cross-reaction of the antibodies with fibronectin of various sources was tested by the Ouchterlony double immunodiffusion system, as described previously.7 In this study, we further tested cross-reactivity with collagen types I; III, IV, and V by enzyme-linked immunosorbent assay which was performed as described previously.7
July 15. 1985 Am J Obstet Gynecol
Fig. 2. Cytotrophoblastic cell columns (A) and decidual tissue of 7 weeks' gestation stained with anti-fibronectin antibodies. Note positive staining of non villous trophoblasts (A) and virtually negative staining of decidual tissue (B). ( x 180.)
(B)
Histologic technique. The distribution of fibronectin was studied by indirect immunofluorescence staining, as described previously.6 Briefly, unfixed cryostat sections (4 f.Lm) were serially incubated with the anti-fibronectin antibodies and fluorescein isothiocyanateconjugated goat anti-rabbit immunoglobulin (Behringwerke, Marburg) . Each incubation step was carried out at 4° C. Control sections were treated with nonimmune rabbit serum instead of anti-human fibronectin .
Results Antibodies. The antibodies formed a precipitin line with human placental fibronectin, and the line was completely fused to that of human plasma fibronectin (data not shown). Because of this complete cross-reactivity, we used the antibodies for immunofluorescence staining of placental fibronectin . Enzyme-linked immunosorbent assay showed that the antibodies did not cross-react with any type of collagen tested (data not shown). Immunofluorescence staining. In the first-trimester chorionic villi, fluorescence of fibronectin was demonstrated in the trophoblastic basement membranes
Volume 152 Number 6, Part 1
Fibronectin distribution in placenta 717
Fig. 3. Chorionic villi of 13 weeks' gestation stained with antifibronectin antibodies. Note that fluorescence in the fetal capillary walls is stronger than that in the trophoblastic basement membranes. (x 240.)
Fig. 4. A chorionic villus of 20 weeks' gestation stained with anti-fibronectin antibodies. Note that fluorescence in the fetal capillary walls is predominant. (X 240.)
and in the connective tissue core of the villi (Fig. 1). Fluorescence in the trophoblastic basement membranes was observed in almost all of the villi. The villous stroma showed a loosely organized network of fibrillar fluorescence. Neither syncytiotrophoblasts nor cytotrophoblasts were stained with the antibodies. In contrast, strong fluorescence of fibronectin was found in the pericellular matrices of non villous trophoblasts, namely, the cells forming cytotrophoblastic cell columns and cytotrophoblastic shell (Fig. 2, A). Decidual tissue was only faintly stained with the antibodies (Fig. 2, B). After 10 weeks' gestation, fibronectin was mainly distributed around the fetal capillaries (Fig. 3). Fluorescence in the trophoblastic basement membranes was not so prominent as in the earlier villi. Interruptions of the basement membrane fluorescence were occasionally observed. In the second-trimester placentas, fibronectin was seen around the fetal vessels and, to a lesser extent, in
Fig. 5. Chorionic villi of 40 weeks' gestation stained with antifibronectin antibodies (A and B). These specimens were dissected after the perfusion of the placenta with citra ted saline solution through the umbilical vein. Note prominent fluorescence in the fetal vessel walls and the absence of fluorescence in the trophoblastic basement membranes (A). The areas of fibrinoid necrosis and intervillous fibrin are strongly positive (B). (A, x 300, B, x 240.)
the villous stroma (Fig. 4). The trophoblastic basement membranes were no longer recognized as continuous structures. In term placental villi, fibronectin was stained predominantly around the fetal vessels (Fig. 5). The stainings in the vessel walls were far more dense than those of second-trimester villi. The trophoblastic basement membranes were not stained in almost any of the villi (Fig. 5, A). The syncytiotrophoblast layer was virtually negative, as in the earlier villi. The areas of fibrinoid necrosis and intervillous fibrin were positively stained (Fig. 5, B). In the sections of larger chorionic villi, fluorescence of fibronectin was densely distributed in a laminar fashion around the fetal stem vessels (not shown).
Comment The present study indicated that both early and term chorionic villi contain fibronectin as a connective tissue
718
Yamaguchi et al.
component. However, the distribution of fibronectin was different between early and term chorionic villi. In early chorionic villi, fibronectin was localized mainly in the trophoblastic basement membranes. Fluorescence of fibronectin disappeared from the trophoblastic basement membranes with the advance of pregnancy, although studies with the electron microscope have demonstrated that the trophoblastic basement membrane shows an increase in membrane thickness as the placenta matures. 8 Therefore, compositional changes must occur in the trophoblastic basement membrane during the development of chorionic villi. The present study also revealed that the pericellular matrices of nonvillous trophoblasts of early chorionic villi were stained with anti-fibronectin antibodies, whereas those of villous trophoblasts were not. Boyd and Hamilton 8 stated that there are numerous mitotic figures in cytotrophoblastic cell columns and cytotrophobias tic shell of early chorionic villi, thus indicating that proliferation is occurring at a high rate. Therefore, the present findings are compatible with the previous observations that actively proliferating undifferentiated cells produce increased amounts of fibronectin. g , 10 It is likely that trophoblasts have an ability to synthesize fibronectin when they are rapidly proliferating, but lose it as they mature. In the term placentas, fibronectin was localized around the fetal vessels and in the stroma of the villi. Biochemical characterization of term p'lacental fibronectin recently reported by Zhu et al!and from our laboratory' demonstrated that placental fibronectin differs from plasma fibronectin in the carbohydrate structure. This suggests that placental fibronectin is of tissue origin(s) other than plasma. Because of the dense deposition pattern around the fetal vessels, it is unlikely that this fibronectin is of trophoblastic origin. Therefore, term placental fibronectin may be derived from the cells in the connective tissue core, including fibroblasts and endothelial cells; both cell types have been shown to synthesize fibronectin in vitro." 2, II The changes in the distribution observed in this study
July 15, 1985 Am J Obstet Gynecol
suggest that placental fibronectin may be produced by different cell types and may play different biologic roles according to the developmental stage of chorionic villi. Fibronectin of early chorionic villi may act not simply as a tissue-supporting material but as a modulator of proliferation and organization of trophoblastic tissues. It would be quite interesting, therefore, to study the effects of fibronectin on the cells of trophectoderm, with the use of cultured animal embryos. We are grateful to Dr. Hiroshi Nagai for the generous supply of human placentas. REFERENCES 1. Ruoslahti E, Engvall E, Hayman EG. Fibronectin: current concepts of its structure and functions. Collagen Res 1981;1:95. 2. Yamada KM. Cell surface interactions with extracellular materials. Annu Rev Biochem 1983;52:761. 3. Bray BA. Presence of fibronectin in basement membranes and acidic structural glycoproteins from human placenta and lung. Ann NY Acad Sci 1978;312:142. 4. Zhu BC-R, Fisher SF, Pande H, Calaycay J, Shively JE, Laine RA. Human placental (fetal) fibronectin: increased glycosylation and higher protease resistance than plasma fibronectin. J Bioi Chem 1984;259:3962. 5. Isemura M, Yamaguchi Y, Munakata H, Aikawa J, Kan M, Yamane I, Yosizawa Z. Isolation and characterization of human placenta fibronectin. J Biochem (Tokyo) 1984; 96:163. 6. Kojima N, Isemura M, Yosizawa Z, Ono T, Shinada S, Soga K, Aoyagi Y, Ichida F. Distribution of fibronectin in fibrotic human livers at various states. TohokuJ Exp Med 1981;135:403. 7. Yamaguchi Y, Isemura M, Kosakai M, Sato A, Suzuki M, Kan M, Yosizawa Z. Characterization of fibronectin from fetal human plasma in comparison with adult plasma fibronectin. Biochim Biophys Acta 1984;790:53. 8. BoydJD, Hamilton W. The human placenta. Cambridge: W. Heffer & Sons Ltd, 1970. 9. Linder E, Vaheri A, Ruoslahti E, Wartiovaara J. Distribution of fibroblast surface antigen in the developing chick embryo.J Exp Med 1975;142:41. 10. Linder E, Stenman S, Lehto V-P, Vaheri A. Distribution of fibronectin in human tissues and relationship to other connective tissue components. Ann NY Acad Sci 1978; 312:151. 11. Jaffe EA, Mosher DF. Synthesis of fibronectin by cultured human endothelial cells. J Exp Med 1978; 147: 1779.
Volume 152 Number 6. Part I
8. Dhindsa DS, Hovensland AS, Metcalfe J. Resting hemodynamic and oxygen transport in unanesthetized adult cats. Respir Physiol 1979;38 : 105. 9. Korner PI, Smith D. Cardiac output in normal unanaesthetized and anaesthetized rabbits. Aust J Exp Bioi Med Sci 1954;32 :499. 10. Duncan S, Lewis B. Maternal placental and myometrial blood flow in the pregnant rabbit.J PhysioI1969;202 :47 1. I I . Meschia G. Circulation to female reproductive organs. In : Handbook of Physiology-The ca rdiovascular system I II . Bethesda: American Phsyiological Society, 1983:24 1. 12. Rosenfeld CR. Distribution of cardiac output in ovine pregnancy. AmJ Physiol 1977;232: H23J. 13. Myers SA, SparksJW, Makowski EL, Meschia G, Battaglia
14. IS . 16. 17.
FC. Relationship between placental blood flow and placental fetal size in guinea pig. Am J Physiol 1982; 243:H404. Moll W, Kastendieck E. Transfer of N2 0, CO and HTO in the artificially perfused guinea pig placenta. Respir Physiol 1977;29:283. Wilkening RB, Anderson S, Martensson L, Meschia G. Placental transfer as a function of uterine blood flow. Am J Physiol 1982;242( 11):H429-36. Block SM,Johnson RL, SparksJW, Battaglia Fe. Uterine metabolism of the pregnant guinea pig as a function of gestational age (in preparation). Rosner B. Fundamentals of biostatistics. Boston: Duxbury Press, 1982.
Changes in the distribution of fibronectin in the placenta during normal human pregnancy Yu Yamaguchi, M.D., Mamoru Isemura, Ph.D., Zensaku Yosizawa, Ph.D., Kosei Kurosawa, M.D., Kaoru Yoshinaga, M.D., Akira Sato, M.D., and Masakuni Suzuki, M.D. Sendai, Japan The distribution of fibronectin, a major extracellular glycoprotein with various activities that affect the proliferation and differentiation of cells, was studied by immunofluorescence staining in first-, second- and third-trimester placentas from normal human pregnancy. In early chorionic villi, fibronectin was localized mainly in the trophoblastic basement membranes; this fluorescence became weaker after 10 weeks' gestation. In term placenta, fibronectin was densely deposited around the fetal vessels but not in the trophoblastic basement membranes. Both syncytiotrophoblasts and cytotrophoblasts of the villous epithelium were virtually negative throughout pregnancy. However, the pericellular matrices of nonvillous trophoblasts in early chorionic villi were strongly stained. These findings suggest that fibronectin plays an important role in the proliferation of trophoblastic cells and the tissue organization of the placenta. (AM J OesTET GYNECOL 1985;152:715-8.)
Key words: Fibronectin, human placenta, trophoblast, basement membrane, immunofluorescence, developmental change Fibronectin is a high molecular weight glycoprotein with a variety of biologic activities, including cell adhesion, embryonic cell migration, wound healing, and differentiation of cells." 2 It is present in soluble form in plasma and amniotic fluid, and in insoluble form in extracellular matrix. The extract of human term placenta has been shown to contain a protein antigenically indistinguishable from plasma fibronectin/ and, recently, Zhu et aI.' and we; have reported the isolation
and biochemical characterization of human placental fibronectin. The present study was designed to show the distribution of fibronectin in the placenta during normal human pregnancy by indirect immunofluorescence staining. We report here that the distribution of fibronectin changes during the development of chorionic villi.
From the Departments of Obstetrics and Gynecology, Medicine, and Biochemistry, Tohoku University School of Medicine. Supported in part by a grant-in-aid for scientific research from the Ministry of Education, Science and Culture of japan. Received for publication October 25, 1984; revised February 21, 1985; accepted February 25, 1985. Reprint requests: Dr. Yu Yamaguchi, Department of Obstetrics and Gynecology, Tohoku University School of Medicine, Sendai 980, japan.
Placenta. Human trophoblastic tissues were obtained from pregnancies terminated in the first and second trimesters by legal abortion and from normal pregnancies at term immediately after delivery. In the case of term placentas, portions of the central cotyledon were selectively dissected and used for staining. All tissues were examined histologically to assure normal
Material and methods
715
716
Yamaguchi et al.
Fig. 1. Chorionic villi of (A) 4 weeks' and (B) 7 weeks' gestation stained by immunofluorescence technique with anti-fibronectin antibodies. Note linear, continuous pattern of fluorescence along the trophoblastic basement membranes. (A, x 90; B, x 180.)
morphologic features before being immunohistochemically stained. The numbers of placentas studied were 10, 5, and lO for first, second, and third trimesters, respectively. Preparation of fibronectin. Human plasma fibronectin was obtained in a pure form from adult human plasma, as described previously.· Human placental fibronectin was isolated according to the method described previously.5 Preparation of antibodies. Anti-human fibronectin antibodies were prepared by immunizing rabbits with plasma fibronectin and absorbed with fibronectin-depleted human plasma which had been coupled to Sepharose 4B, as described previously.· The antibodies were shown to produce a single precipitin arc when reacted with human plasma by immunoelectrophoresis." Cross-reaction of the antibodies with fibronectin of various sources was tested by the Ouchterlony double immunodiffusion system, as described previously.7 In this study, we further tested cross-reactivity with collagen types I; III, IV, and V by enzyme-linked immunosorbent assay which was performed as described previously.7
July 15. 1985 Am J Obstet Gynecol
Fig. 2. Cytotrophoblastic cell columns (A) and decidual tissue of 7 weeks' gestation stained with anti-fibronectin antibodies. Note positive staining of non villous trophoblasts (A) and virtually negative staining of decidual tissue (B). ( x 180.)
(B)
Histologic technique. The distribution of fibronectin was studied by indirect immunofluorescence staining, as described previously.6 Briefly, unfixed cryostat sections (4 f.Lm) were serially incubated with the anti-fibronectin antibodies and fluorescein isothiocyanateconjugated goat anti-rabbit immunoglobulin (Behringwerke, Marburg) . Each incubation step was carried out at 4° C. Control sections were treated with nonimmune rabbit serum instead of anti-human fibronectin .
Results Antibodies. The antibodies formed a precipitin line with human placental fibronectin, and the line was completely fused to that of human plasma fibronectin (data not shown). Because of this complete cross-reactivity, we used the antibodies for immunofluorescence staining of placental fibronectin . Enzyme-linked immunosorbent assay showed that the antibodies did not cross-react with any type of collagen tested (data not shown). Immunofluorescence staining. In the first-trimester chorionic villi, fluorescence of fibronectin was demonstrated in the trophoblastic basement membranes
Volume 152 Number 6, Part 1
Fibronectin distribution in placenta 717
Fig. 3. Chorionic villi of 13 weeks' gestation stained with antifibronectin antibodies. Note that fluorescence in the fetal capillary walls is stronger than that in the trophoblastic basement membranes. (x 240.)
Fig. 4. A chorionic villus of 20 weeks' gestation stained with anti-fibronectin antibodies. Note that fluorescence in the fetal capillary walls is predominant. (X 240.)
and in the connective tissue core of the villi (Fig. 1). Fluorescence in the trophoblastic basement membranes was observed in almost all of the villi. The villous stroma showed a loosely organized network of fibrillar fluorescence. Neither syncytiotrophoblasts nor cytotrophoblasts were stained with the antibodies. In contrast, strong fluorescence of fibronectin was found in the pericellular matrices of non villous trophoblasts, namely, the cells forming cytotrophoblastic cell columns and cytotrophoblastic shell (Fig. 2, A). Decidual tissue was only faintly stained with the antibodies (Fig. 2, B). After 10 weeks' gestation, fibronectin was mainly distributed around the fetal capillaries (Fig. 3). Fluorescence in the trophoblastic basement membranes was not so prominent as in the earlier villi. Interruptions of the basement membrane fluorescence were occasionally observed. In the second-trimester placentas, fibronectin was seen around the fetal vessels and, to a lesser extent, in
Fig. 5. Chorionic villi of 40 weeks' gestation stained with antifibronectin antibodies (A and B). These specimens were dissected after the perfusion of the placenta with citra ted saline solution through the umbilical vein. Note prominent fluorescence in the fetal vessel walls and the absence of fluorescence in the trophoblastic basement membranes (A). The areas of fibrinoid necrosis and intervillous fibrin are strongly positive (B). (A, x 300, B, x 240.)
the villous stroma (Fig. 4). The trophoblastic basement membranes were no longer recognized as continuous structures. In term placental villi, fibronectin was stained predominantly around the fetal vessels (Fig. 5). The stainings in the vessel walls were far more dense than those of second-trimester villi. The trophoblastic basement membranes were not stained in almost any of the villi (Fig. 5, A). The syncytiotrophoblast layer was virtually negative, as in the earlier villi. The areas of fibrinoid necrosis and intervillous fibrin were positively stained (Fig. 5, B). In the sections of larger chorionic villi, fluorescence of fibronectin was densely distributed in a laminar fashion around the fetal stem vessels (not shown).
Comment The present study indicated that both early and term chorionic villi contain fibronectin as a connective tissue
718
Yamaguchi et al.
component. However, the distribution of fibronectin was different between early and term chorionic villi. In early chorionic villi, fibronectin was localized mainly in the trophoblastic basement membranes. Fluorescence of fibronectin disappeared from the trophoblastic basement membranes with the advance of pregnancy, although studies with the electron microscope have demonstrated that the trophoblastic basement membrane shows an increase in membrane thickness as the placenta matures. 8 Therefore, compositional changes must occur in the trophoblastic basement membrane during the development of chorionic villi. The present study also revealed that the pericellular matrices of nonvillous trophoblasts of early chorionic villi were stained with anti-fibronectin antibodies, whereas those of villous trophoblasts were not. Boyd and Hamilton 8 stated that there are numerous mitotic figures in cytotrophoblastic cell columns and cytotrophobias tic shell of early chorionic villi, thus indicating that proliferation is occurring at a high rate. Therefore, the present findings are compatible with the previous observations that actively proliferating undifferentiated cells produce increased amounts of fibronectin. g , 10 It is likely that trophoblasts have an ability to synthesize fibronectin when they are rapidly proliferating, but lose it as they mature. In the term placentas, fibronectin was localized around the fetal vessels and in the stroma of the villi. Biochemical characterization of term p'lacental fibronectin recently reported by Zhu et al!and from our laboratory' demonstrated that placental fibronectin differs from plasma fibronectin in the carbohydrate structure. This suggests that placental fibronectin is of tissue origin(s) other than plasma. Because of the dense deposition pattern around the fetal vessels, it is unlikely that this fibronectin is of trophoblastic origin. Therefore, term placental fibronectin may be derived from the cells in the connective tissue core, including fibroblasts and endothelial cells; both cell types have been shown to synthesize fibronectin in vitro." 2, II The changes in the distribution observed in this study
July 15, 1985 Am J Obstet Gynecol
suggest that placental fibronectin may be produced by different cell types and may play different biologic roles according to the developmental stage of chorionic villi. Fibronectin of early chorionic villi may act not simply as a tissue-supporting material but as a modulator of proliferation and organization of trophoblastic tissues. It would be quite interesting, therefore, to study the effects of fibronectin on the cells of trophectoderm, with the use of cultured animal embryos. We are grateful to Dr. Hiroshi Nagai for the generous supply of human placentas. REFERENCES 1. Ruoslahti E, Engvall E, Hayman EG. Fibronectin: current concepts of its structure and functions. Collagen Res 1981;1:95. 2. Yamada KM. Cell surface interactions with extracellular materials. Annu Rev Biochem 1983;52:761. 3. Bray BA. Presence of fibronectin in basement membranes and acidic structural glycoproteins from human placenta and lung. Ann NY Acad Sci 1978;312:142. 4. Zhu BC-R, Fisher SF, Pande H, Calaycay J, Shively JE, Laine RA. Human placental (fetal) fibronectin: increased glycosylation and higher protease resistance than plasma fibronectin. J Bioi Chem 1984;259:3962. 5. Isemura M, Yamaguchi Y, Munakata H, Aikawa J, Kan M, Yamane I, Yosizawa Z. Isolation and characterization of human placenta fibronectin. J Biochem (Tokyo) 1984; 96:163. 6. Kojima N, Isemura M, Yosizawa Z, Ono T, Shinada S, Soga K, Aoyagi Y, Ichida F. Distribution of fibronectin in fibrotic human livers at various states. TohokuJ Exp Med 1981;135:403. 7. Yamaguchi Y, Isemura M, Kosakai M, Sato A, Suzuki M, Kan M, Yosizawa Z. Characterization of fibronectin from fetal human plasma in comparison with adult plasma fibronectin. Biochim Biophys Acta 1984;790:53. 8. BoydJD, Hamilton W. The human placenta. Cambridge: W. Heffer & Sons Ltd, 1970. 9. Linder E, Vaheri A, Ruoslahti E, Wartiovaara J. Distribution of fibroblast surface antigen in the developing chick embryo.J Exp Med 1975;142:41. 10. Linder E, Stenman S, Lehto V-P, Vaheri A. Distribution of fibronectin in human tissues and relationship to other connective tissue components. Ann NY Acad Sci 1978; 312:151. 11. Jaffe EA, Mosher DF. Synthesis of fibronectin by cultured human endothelial cells. J Exp Med 1978; 147: 1779.