Objectives:To characterize changes in myometrial contracticle proteins and myosin heavy chain (MHC) isoforms during ovine fetal and neonatal development and after pregnancy. We hypothesized that ovine myometrium demonstrates progressive cellular differentiation and maturation which begins in utero and extends into the postnatal period, and that pregnancy causes further cellular alterations.
Methods:Myometrium was obtained from female fetal (72- to 140-days of gestation, n = 19; term = ∼145 days), postnatal (1 day to 3 months, n = 25), and parous noncycling nonpregnant (n = 9) sheep to measure total and soluble proteins, actin, MHC, and MHC isoforms. Contractile proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and expression of 200-kD MHC isoforms were determined with Western immunoblots.
Results:The contents of total and soluble proteins and actin and total myosin gradually increase (P < .003) during ovine development. Although the contribution of smooth-muscle 204-kD MHC increased (P < .001) from 23 ± 8% of total MHC at < 100 days of gestation to 75 ± 2% 3 to 4 months postnatally, the 200-kD species fell proportionately. Before birth, MHC-B, a fetal isoform, is the predominant 200-kD protein; postnatally, it is replaced by SM2, demonstrating a switch from a synthetic to a mature contractile smooth-muscle phenotype. Pregnancy is associated with further increases in actin contents and redistribution of the contents of the 204-kD and SM2 MHC isoforms.
Conclusions:Although the fetal and postnatal uterus has no known functional demand, ovine myometrial differentiation and maturation begin in the midtrimester and continue throughout the postnatal period. Thus, changes in smooth-muscle phenotype occur prenatally, as evidenced by a switch from MHC-B to SM2, which may signal completion of organ development and preparation for adult function. Pregnancy results in further modifications in myometrial proteins.
1. Bartol FF, Wiley AA, Spencer TE, Vallet JL, Christenson RK. Early uterine development in pigs. J Reprod Fertil1993;48:99-116.
2.
2. Christenson RK, Leymaster KA, Young LD. Justification of unilateral hysterectomy- ovariectomy as a model to evaluate uterine capacity in swine. J Anim Sci1987;65:738-744.
3.
3. Wiley AA, Bartol FF, Barron DH. Histogenesis of the ovine uterus. J Anim Sci1987;64:1262-1269.
4.
4. Marion GB, Gier HT. Ovarian and uterine embryogenesis and morphology of the non- pregnant female mammal. J Anim Sci1971;32:24-47.
5.
5. Baskin LS, Hayward P, Young P, Cunha GR. Role of mesenchymal-epithelial interactions in normal bladder development. J Urol1996;156:1820-1827.
6.
6. Cunha GR, Young P, Brody JR. Role of uterine epithelium in the development of myometrial smooth muscle cells. Biol Reprod1989;40:861-871.
7.
7. Brody JR, Cunha GR. Histologic, morphometric, and immunocytochemical analysis of myometrial development in rats and mice: I. Normal development. Am J Anat1989;186:1-20.
8.
8. Bal HS, Getty R. Postnatal growth of the swine uterus from birth to six months. Growth1970;34:15-30.
9.
9. Yamamoto I. An electron microscope study of development of uterine smooth muscle. J Electronmicrosc1961;10:145-160.
10.
10. Konishi I, Fujii S, Okamura H, Mori T. Development of smooth muscle in the human fetal uterus: An ultrastructural study. J Anat1984;139:239-252.
11.
11. Owens GK. Regulation of differentiation of vascular smooth muscle cells. Physiol Rev1995;75:487-517.
12.
12. Miano JM, Cserjesi P, Ligon KL, Periasamy M, Olson EN. Smooth muscle myosin heavy chain exclusively marks the smooth muscle lineage during mouse embryogenesis. Circ Res1994;75:803-812.
13.
13. Emerson CP Jr, Bernstein SI. Molecular genetics of myosin. Annu Rev Biochem1987;56:695-726.
14.
14. Somlyo AP. Myosin isoforms in smooth muscle: How may they affect function and structure?J Muscle Res Cell Motil1993;14:557-563.
15.
15. Kelley CA, Adelstein RS. Characterization of isoform diversity in smooth muscle myosin heavy chains. Can J Physiol Pharmacol1994;72:1351-1360.
16.
16. Kuro-o M, Nagai R, Tsuchimochi H, et al. Developmentally regulated expression of vascular smooth muscle myosin heavy chain isoforms. J Biol Chem1989;264:18272-18276.
17.
17. Simons M, Wang M, McBride W, et al. Human nonmuscle myosin heavy chains are encoded by two genes located on different chromosomes. Circ Res1991;69:530-539.
18.
18. Warrick HM, Spudich JA. Myosin structure and function in cell motility. Annu Rev Cell Biol1987;3:379-421.
19.
19. Kuro-o M, Nagai R, Nakahara K, et al. cDNA cloning of a myosin heavy chain isoform in embryonic smooth muscle and its expression during vascular development and in arteriosclerosis. J Biol Chem1991;266:3768-3773.
20.
20. Chern J, Kamm KE, Rosenfeld CR. Smooth muscle myosin heavy chain isoforms are developmentally regulated in male fetal and neonatal sheep. Pediatr Res1995;38:697-703.
21.
21. Arnes YHJM, Rosenfeld CR, Kamm KE. Maturational differences between vascular and bladder smooth muscle during ovine development. Am J Physiol Regul Integrat Comp Physiol2000; 278:R1305-R1313.
22.
22. Rosenfeld CR. Distribution of cardiac output in ovine pregnancy. Am J Physiol1977;232:H231-H235.
23.
23. Rosenfeld CR, Morris FH, Makowski EL, Meschia G, Battaglia F. Circulatory changes in the reproductive tissues of ewes during pregnancy. Gynecol Invest1974;5:252-268.
24.
24. Ipson MA, Rosenfeld CR, Magness RR, Kamm KE. Alterations in myometrial stress during ovine pregnancy and puerperium. Am J Physiol1996;271:R446-R454.
26. Arens Y, Chapados R, Cox B, Kamm KE, Rosenfeld CR. Differential development of umbilical and systemic arteries. II. Contractile proteins. Am J Physiol1998;274:R1815-R1823.
27.
27. Annibale DJ, Rosenfeld CR, Still JT, Kamm KE. Protein content and myosin light chain phosphorylation in uterine arteries during pregnancy. Am J Physiol1990;259:C484-C489.
28.
28. Eddinger TJ, Murphy RA. Developmental changes in actin and myosin heavy chain isoform expression in smooth muscle. Arch Biochem Biophys1991;284:232-237.
29.
29. Seidel CL, Murphy RA. Changes in rat aortic actomyosin content with maturation. Blood Vessels1979;16:98-108.
30.
30. Eddinger TJ, Wolf JA. Expression of four myosin heavy chain isoforms with development in mouse uterus. Cell Motil Cytoskel1993;25:358-368.
31.
31. Jones AW. Vascular smooth muscle. In: Bohr DF, Somlyo AP, Sparks HVJr, eds. Handbook of physiology. Berthesda: American Physiology Society, 1980:253-299.
32.
32. Sparrow MP, Mohammad MA, Arner A, Hellstrand, Ruegg JC. Myosin composition and functional properties of smooth muscle from the uterus of pregnant and non-pregnant rats. Pflugers Arch1988;412:624-633.
33.
33. Cavaille F, Janmot C, Ropert S, D'Albis A. Isoforms of Myosin and actin in human, monkey and rat myometrium. Comparison of pregnant and non-pregnant uterus proteins. Eur J Biochem1986;160:507-513.
