the fine structure of sow lutein cells

The Fine Structure of Sow Lutein Cells PAUL GOODMAN,3 JOHN S. LATTA, RICHARD B. WILSON AND BARNEY KADIS Departments of Anatomy, Pathology, Obstetrics and Gynecology, a7zd the Eppley Cancer Re.search Institute, University of Nebraska College of Medi- cine, Omaha, Nebraska

ABSTRACT The morphological observations described in this reuort are part of a biochemical study of progesterone intermediates using sow ovary. This tissue is exten- sively involved in the production of some steroid hormones. Because the lutein cells are thought to be involved in the synthesis of progesterone and its intermediates and because these cells constitute by size and number the greatest portion of the mass of sow ovary, we confined the morphological investigation to these cells. Sow corpora lutea, fixed with glutaraldehyde and osmium tetroxide were examined by light and electron microscopy.

The lutein cells of the sow are large epithelioid cells with oval nuclei and extensive amounts of cytoplasm. Large masses of highly organized smooth endoplasmic reticulum, many oval mitochondria with tubular cristae, and many lipid droplets are present. Only a few profiles of rough endoplasmic reticulum are seen in any one section, and Golgi membranes cannot by distinguished from other smooth membranes. The smooth endoplasmic reticulum is the major membranous organelle in these luteal cells. Micro- somal preparations from luteal cells must be very rich in fragments of these smooth membranes. The demonstration of many steroidogenic enzyme systems in microsomal preparations lends strong support to the supposition that these enzyme systems reside in the smooth endoplasmic reticulum.

Christensen ('65) has drawn attention to the unusual amount and organization of the smooth endoplasmic reticulum in the interstitial cells of guinea pig testes. This report, an adjunct to a biochemical investigation of the metabolism of progesterone in the sow ovary, deals with some ultrastructural observations of several sow lutein cells.

Smooth membranes isolated from the microsomal fraction of sow ovary homogenates by density gradient fractionation (Fouts, '61) were used in studying some intermediary products in the metabolism of progesterone. One of the authors (B.K.) noting the yield of the smooth membrane fraction was greater than expected asked that the purity of the prep- aration be confirmed by electron microscopy. Subsequent observations of several pellets confirmed the presence of smooth membranes with no contaminating ribosomes, mitochondria1 fragments or nuclei. In addition biochemical checks or purity were performed. The yield of relatively clean smooth membranes in greater quantities than was expected prompted this morphological study on the intact ovary.

We consider the extensive mass of highly organized smooth membranes, and

ANAT. REC., 161: 77-90.

the associated mass of mitochondria and lipid are worthy of description. In addition this report contains a description of a single, highly unusual nucleus that contains an intranuclear membranous system.

MATERIALS AND METHODS

The ovaries utilized in this study were collected under the same conditions as those used in the biochemical investigation save that tissues from non-pregnant and pregnant sows were collected sepa- rately. At this time only tissues from the non-pregnant animals have been studied. The ovaries were removed from slaughtered swine as soon as they reached the cutting floor at the meat packing plant (40-50 minutes after death).4 Thin slices (5 mm) were placed in cold buffered glutaraldehyde (Millonig's buffer, pH 7.2). After approximately two hours of fixation in the glutaraldehyde, the slices were rinsed in buffer and were then placed in fresh buffer for an hour. Small blocks of what grossly were identified as corpora

1 Presented in part before the American Association of Anatomists at Kansas City, Missouri, April 1967.

2 Supported in part by USPHS grant HD 18-06. 3 USPHS Trainee. 4 Material used in this experiment secured through

the courtesy of Swift and Company, Omaha, Nebraska.

77

78 P. GOODMAN, J. S. LATTA, R. B . WILSON AND B. KADIS

lutea were cut from these slices and were postfixed in 1 % buffered osmium tetroxide (Millonig’s buffer, pH 7.2) for three hours. After dehydration in graded alco- hols and propylene oxide, the small blocks of tissue were embedded in Araldite 502. Thick sections stained with toluidine blue were examined to ascertain the presence of granulosa lutein cells in the samples. Thin sections stained with uranyl acetate were examined in either the Philips l O O B or the RCA EMU 3G electron microscope. Several pieces of the glutaraldehyde fixed corpus luteum were postfixed with 10% formalin and embedded in paraffin. Sec- tions of these blocks were stained with hematoxylin and eosin.

OBSERVATIONS-LIGHT MICROSCOPY

Sections of the paraffin embedded corpus luteum contain large oval pale stain- ing cells ranging from 30-50 in diameter. Theca lutein cells as described by Corner (’21) were not seen. Capillaries are abundant, not collapsed and in close proximity to each of the lutein cells. The toluidine blue stained thick sections showed essentially the same histological features as the H & E sections.

OBSERVATIONS-ELECTRON MICROSCOPY

Even at relatively low magnifications in the electron microscope, the smooth endoplasmic reticulum (s.e.r.) is a most out- standing feature of the sow lutein cell (fig. 1). These membranes form extensive highly organized systems in the cytoplasm of the lutein cell. The s.e.r. varies in amount in different portions of the same cell. There may be only a few isolated profiles found dispersed among the mitochondria and lipid droplets, or these membranes may form almost solid masses ranging from 2-25 in diameter. In most of the lutein cells, the mass of the s.e.r. is such that the other cytoplasmic organelles or inclusions are in crowded masses.

The morphological configurations of these smooth membrane systems vary greatly. One variety seen frequently con- sists of layer upon layer of closely packed undilated cisternae or collapsed tubules. In section these membranes may be ar- ranged parallel to each other in longi- tudinal arrays or they may form tightly

swirling whorls very much like a fmger- print (fig. 1 ) . Another commonly observed variation contains widely dilated tubules cut either tangentially or in cross- section, stacked layer upon layer and tightly packed together. This variety of system closely resembles a honeycomb (fig. 2 ) .

Most often, however, a combination of small patches of “honeycomb” are seen dispersed, embedded in a mass of “fingerprint” membranes (fig. 3 ) . Occasionally, mitochondria and/or lipid droplets are found among the masses of s.e.r. (fig. 1).

Were i t not for the unusual mass and structure of the s.e.r., the mitochondria would easily be the most striking feature of the sow lutein cell because of their great numbers. That portion of the lutein cell in figure 1 contains an estimated 150 profiles of mitochondria in section. For the most part, the mitochondria are circu- lar to oval in shape and are from 0.7-1.0

in diameter. The mitochondria1 cristae are tubular or tubulo-vesicular in form (fig. 4). In many sections the poorly de- fined cristae seem to be vesicular in structure (fig. 5). The cytoplasm of these lutein cells is very rich in lipid inclusion droplets, which are often closely associated with the mitochondria.

A few profiles of rough endoplasmic reticulum (r.e.r.) can be found in most sections. They are seen most often as single pairs of membranes studded with ribosomes and crowded between the densely packed mitochondria and lipid droplets (fig. 5). No r.e.r. could be identified among the membranes of the s.e.r. masses. Occasionally, continuity between rough and smooth membranes is noted (fig. 5). Golgi membranes per se are not distinguishable in the profusion of smooth membranes. Clusters of unat- tached ribosomes are seen occasionally between the other organelles (fig. 5 ) . Rarely, lysosome-like or crystalloid bodies are observed.

The nucleus of the sow lutein cell is, for the most part, not unusual. The nuclear membrane is composed of an outer and an inner lamina continuous with each other at the nuclear pores. These two laminae are separate and discrete except a t the nuclear pores. Deep to the inner

THE FINE STRUCTURE OF SOW LUTEIN CELLS 79

lamina, interposed between it and the marginated nuclear chromatin, is an electron dense layer of material of constant thickness (fig. 5) . This dense layer is con- tinuously applied to the deep surface of the inner lamina. It is interrupted only in the region of the nuclear pore, where the inner lamina is continuous with the outer one. The remainder of the nucleus con- sists of finely dispersed nucleoplasm with moderate amounts of clumped chromatin. The single nucleolus is not remarkable.

One section of a highly unique nucleus contains, among other things, a relatively large mass of tubules (fig. 6). They are formed by smooth membranes very similar to the s.e.r. These tubules occupy almost half of the nucleus. In addition to the com- pact mass of tubular membranes located in the central portion of the nucleus, there are isolated tubules scattered throughout the rest of the nucleoplasm. The mass of tubules lacks the organization of its cytoplasmic counterpart, the s.e.r. It shows, rather, a large degree of dis- orientation. Unlike the cytoplasmic invagination seen in the same section, these tubular membranes are not isolated by a nuclear membrane. The electron dense zone described above is present on the inner surface of the nuclear membrane both at the periphery and around the in- vaginated cytoplasm. It is not identified surrounding the intranuclear membranous system. Besides these membranes, this unusual nucleus also contains several lipid droplets, a vacuole, a myelin figure, and a lysosome-like inclusion. Like the intranuclear membranes, these structures are not segregated from the nucleoplasm. In addition, there is a cross-section of a finger of cytoplasm located in this nucleus. How- ever, it is definitely segregated from this nucleus by, consecutively, the outer and inner laminae of the nuclear membrane and the layer of electron dense material.

DISCUSSION

The absence of grossly visible placenta- tion in the uterus and the histological de- tails suggest that the corpora lutea used in this study were between 7 and 15 days old and from a non-pregnant sow (Corner, '21). The lack of any other physiological data is regrettable. More than 5,000 swine

are slaughtered daily in the local packing houses and the task of tracking down any information on the animals used either in the biochemical study or in this morphological study was too formidable to con- template.

Because of the adverse conditions under which the tissues for both studies were collected there was originally only the in- tention of looking at the ultrastructure of the tissue that yielded such large quantities of smooth membranes. However, the high degree of organization of the smooth endoplasmic reticulum in such large masses prompted this report despite these adversities.

Descriptions of notable quantities of smooth endoplasmic reticulum in cells involved in steroid metabolism are not rare. They have been reported in the interstitial cells of the testis of the guinea pig (Chris- tensen, '65), the mouse (Christensen and Fawcett, '66), the opossum (Christensen and Fawcett, '61), in the ovaries of the mouse (Yamada and Ishikawa, '60), rat, mink, and armadillo (Enders, '62), and in the fetal adrenal of the armadillo (Enders, Schlafke and Warren, '66) and the human (Ross, Pappas, Lanman and Lind, '58). Now the lutein cell of sow ovary has been added to this Iist (Bjersing, '67; Good- man, Latta, Wilson and Kadis, '67). Even the extensive degree of organization found in the s.e.r. of the sow lutein cell has to a smaller extent been described before. The "whorl" of smooth membranes was seen in the interstitial cell of the mouse by Carr and Carr ('62), and again in the interstitial cell of the guinea pig by Chris- tensen ('65). Enders, Schlafke and War- ren ('66) described s.e.r. with a honeycomb pattern in their article on the fetal adrenal of the armadillo. They considered the widespread dilation of the smooth membrane tubules to be a result of de- generative changes in those cells. The elaboration of membranes and the arrang- ing of these membranes into highly organized systems requires a great deal of energy. The manufacturing of the neces- sary enzyme systems and substrates and the production of the energy needed to pro- duce the membranes must be character- istics of an actively vital cell rather than a degenerating cell. We feel the high degree

80 P. GOODMAN, J. S. LATTA, R. B. WILSON A N D B. KADIS

of organization seen in the s.e.r. of the sow lutein cell is therefore more probably an indication of high metabolic activity than of degeneration (Bjersing, ’67). The presence of many mitochondria in these cells would tend to support the hypothesis of high metabolic activity.

The literature on the biochemical activi- ties of various fractions of homogenized cells is quite extensive (DeDuve, Wattiaux and Baudhuin, ’62). One fraction, the microsomal, is of interest to us here. Ex- actly which cellular organelles and inclusions are present in this fraction depend a great deal on the density gradient media and methods utilized to effect the separa- tion (Schneider, ’59). Usually, the microsomes include all the particulate matter that remains unsedimented after being spun at 10,000XG and that is found in the residue after spinning at 100,000XG. Among the morphological entities that may be present in this fraction are the s.e.r., the r.e,r. with attached ribosomes, the Golgi membranes and possibly fragments of ruptured plasma membranes or ruptured mitochondria. Lysosomes are sometimes isolated in this fraction.

The cellular production of steroid hormones by the ovary, testis, or adrenal gland involves many enzymes located in the microsomal fraction, (Ball and Kadis, ’65; Kadis, ’66; Koritz, ’64; Lynn and Brown, ’58; Shikita and Tamaoki, ’65; Harding, Wilson, Wong and Nelson, ’65; and Chamberlain, Jagarinec and Ofner, ’65). In addition the placenta and liver contain some of the same enzymes in their microsomal fractions (Ryan, ’59; Jellinck, Lazier, and Copp, ’65; Bucher and McGar- rahan, ’56; and Wilcox and Engel, ’65). In general, any steroid endocrine organ is capable of producing any of the steroid hormones or their intermediaries. Al- though one type of hormone usually pre- dominates, androgen, etc., the other metabolites may be present in amounts too small to measure without great dif- ficulty. These tissues seem to follow the same biosynthetic pathway from acetate to cholesterol and pregnenolone and seem to have similar enzymes with similar subcellular locations (Ryan and Smith, ’65; Dorfman and Ungar, ’65).

The lutein cell of the sow offers addi- tional proof that the microsomes involved in steroidogenesis are derived from the smooth membranes. The extensive pre- ponderance of the s.e.r. over identifiable Golgi membranes or the r.e.r. is obvious. The microsomal fraction of this tissue, rich in stereoidogenic enzymes (Ball and Kadis, ’65; Kadis, ’66), must be composed of vesicles and fragments derived mainly from the s.e.r. However, we cannot ignore the fact that these microsomes were isolated from homogenates of the entire ovary and not of corpora lutea alone, and therefore, cannot state with absolute certainty that the smooth membranes of the lutein cells are definitely the organelles which contain the steroidogenic enzymes identified in the microsomal studies on sow ovary.

Mitochondria1 enzymes play an im- portant role in steroid metabolism also (Toren, Menon, Forchielli and Dorfman, ’64), and in addition are involved in fur- nishing the energy requirements of these highly active tissues. It is obvious that mitochondria are very abundant in these sow lutein cells. The tubular morphology of the mitochondria1 cristae is consistent with that seen in other steroid endocrine tissues. The mitochondria are rather uni- form in both size and shape. There are none of the large mitochondria noted in rat adrenal cortex (Belt and Pease, ’56). Nor were any cup-shaped mitochondria observed as has been reported in the rat testis (Christensen and Chapman, ’59; Enders, ’62; Enders and Lyons, ’64).

The electron dense layer of material on the deep surface of the nuclear membrane has been described (Patrizi and Poger, ’67; Fawcett, ’66). It is seen in tissues that have been fixed in glutaraldehyde and postfixed in osmium. Patrizi and Poger (’67) have proposed the name “nuclear limiting zone” or “Zonula Nucleum Limitans” for this structure.

With the exception of the one isolated observation noted above, the large, oval nuclei of the lutein cell appear quite normal. The presence of some form of intranuclear membrane has been reported in both mammalian and non-mammalian tissues. Kessel (’66) has described “intranuclear annulate lamellae” in the oocytes

THE FINE STRUCTURE OF SOW LUTEIN CELLS 81

of several species of tunicates. Annular membranes have been reported within the nuclei of human endometrial gland cells, (Dubrauszky and Pohlmann, '61 ; Clyman '63). The nuclei of indifferent cells in the immature calf testis contain similar intranuclear membranes (Nicander, Abdel- Raouf and Crabo, '61). Bucciarelli ('66) has described Golgi-like intranuclear membranes in virus-infected tissues of an in- tracranial chicken sarcoma. Mori and Onoe ('67) have described intranuclear inclusions in neoplastic human renal cells.

In comparing the intranuclear membranes observed in a single luteal cell with those described in the literature, some differences in the extent and type of membranes present are noted. In the nuclei of the human endometrial gland cells these membranes are described as canalicular and are associated with the nucleolus. In calf testis they are described as vacuoles in the nucleolus. Those found in tunicate oocytes are almost identical in structure to its nuclear membrane. Closest in morphology to the membranes we have described are the Golgi-like vesicles and tubules seen in a Rous sarcoma cell nucleus and the intranuclear inclusions in the renal neoplasm. In the reports known to us the intranuclear membranes are not as numerous or as massive as those described in this paper.

While we have no explanation for this phenomenon, it is worth noting that there is a common factor shared by many of the cells in which intranuclear membranes have been described. Most of the cells involved are those which undergo repeated mitoses. One of two processes may ex- plain the formation of intranuclear inclusions. A portion of invaginating cytoplasm may have been pinched off in the reconstruction of the nucleus with subsequent loss of membranous continuity with the remainder of the cytoplasm and de- terioration of its encircling membrane. Alternately, in the process of mitosis some of the cytoplasmic subunits may have been caught inside the regenerating nuclear membrane. The lipid droplets and the membrane bound inclusion body seen in the sow lutein cell described above, lend support to either explanation.

LITERATURE CITED Ball, H., and B. Kadis 1965 Steroid hydroxyla-

tion. 11. Intracellular location of 17 alpha hydroxylase and its substrate specificity in sow ovary. Arch. Biochem., 110: 427431.

Belt, W. D., and D. C. Pease 1965 Mitochondria1 structure in sites of steroid secretions. J. Bio- phys. Biochem. Cytol., 2 (Suppl.): 369-374.

Bjersing, Lars 1967 On the ultrastructure of granulosa lutein cells in porcine corpus luteum. Z . Zellforsch, 82: 187-211.

Bucciarelli, E. 1966 Intranuclear cisternae re- sembling structures of the Golgi complex. J. Cell Biol., 30: 664-665.

Bucher, N. L., and K. McGarrahan 1956 The biosynthesis of cholesterol from acetate I-&& by cellular fractions of rat liver. J. Biol. Chem., 222: 1-15.

Carr, I., and J. Carr 1962 Membranous whorls in the testicular interstitial cell. Anat. Rec., 244:

1965 Catabolism of c-19 steroids by subcellular fractions of mammalian and avian tissues. Steroids,

Christensen, A. K. 1965 The fine structure of testicular interstitial cells in guinea pigs. J. Cell Biol., 26: 911-935.

Christensen, A. K., and G . B. Chapman 1959 Cup-shaped mitochondria in interstitial cells of albino rat testis. Exp. Cell Res., 18: 576-579.

Christensen, A. K., and D. W. Fawcett 1961 The normal fine structure of opossum testicular interstitial cells. J. Biophys. Biochem. Cytol., 9:

1966 The fine structure of testicular

145-146. Chamberlain, J., N. Jagarinec and P. Ofner

Suppl., 11, 1-12.

653-670.

interstitial cells in mice. Am. J. Anat., 218: 551-572.

Clyman, M. J. 1963 A new structure observed in the nucleolus of the human endometrial epi- thelial cells. Amer. J. Obstet. and Gynec., 86: 43-32.

Corner, G. W. 1921 Cyclic changes in the ovaries and uterus of the sow and their relation to the mechanism of implantation. Contr. Em- bryol. Carnex Instn., 13: 117-146.

1962 Distribution of enzymes between subcellular fractions in animal tissues. Advances Enzym.,

Dorfman, R. I., and F. Ungar 1965 Metabolism of Steroid Hormones. Academic Press, New York. Chap. 11, 23.

Dubrauszky, V., and G. Pohlmann 1961 Die ultrastruktur des korpus endometriums wahrend des cyclus. Arch. Gynaek., 196: 180-199.

Enders, A. C. 1962 Observations on the fine structure of lutein cells. J. Cell Biol., 12: 101- 113.

Enders, A. C., and W. R. Lyons 1964 Observa- tions on the fine structure of lutein cells. 11. The effects of hypophysectomy and mammotrophic hormone in the rat. J. Cell Biol., 22: 127-141.

1966 Cytology of the fetal zone of the adrenal gland of the armadillo.

DeDuve, C., R. Wattiaux and P. Baudhuin

24: 291-358.

Enders, A. C., S . Schlafke and R. Warren

Anat. Rec., 254: 807-822.

82 P. GOODMAN, J. S. LATTA, R. B. WILSON AND B. XADIS

Fawcett, D. 1966 An Atlas of Fine Structure: The Cell. W. B. Saunders Company, Philadel- phia, Pennsylvania, pp. 4 0 4 2 .

Fouts, J. R. 1961 The metabolism of drugs by subfractions of hepatic microsomes. Biochem. Biophys. Res. Comm., 6: 373-378.

Goodman, P., J. S. Latta, R. B. Wilson and B. Kadis 1967 Massive smooth endoplasmic reticulum in porcine granulosa lutein cells. Anat. Rec., 157: 249-250.

Harding, B. W., L. D. Wilson, S. H. Wong and D. G. Nelson 1965 Electron carriers of the rat adrenal and the 11-beta-hydroxylating system. Steroids, Suppl. 11, 51-77.

1965 Nature of the water-soluble estrogen metabolites formed by rat liver in nitro. Canad. J. Biochem., 43: 1774-1776.

Kadis, B. 1966 Steroid hydroxylations V. Intra- cellular location of 16 alpha-hydroxylase and its substrate specificity in sow ovary. Biochemistry, 5: 3604-3608.

Kessel, R. G. 1966 Ultrastructure and relation- ships of ooplasmic components in tunicates. Acta Embryol. Morph. Exp., 9: 1-24.

Koritz, S. B. 1964 The conversion of pregnenolone to progesterone by small particles from rat adrenal. Biochemistry, 3: 1098-1102.

Lynn, W. S., Jr., and R. H. Brown 1958 The conversion of progesterone to androgens by testes. J. Biol. Chem., 232: 1015-1029.

Mori, M., and Tamenori Onoe 1967 A n electron microscopic study on the formation of intranuclear inclusions. J. J. Electron Microscopy, 16: 137-142.

Jellinck, P. H., C. Lazier and M. L. Copp

Nicander, L., M. Abdel-Raouf and B. Crabo 1961 On the ultrastructure of the seminiferous tubules in bull calves. Acta Morph. Neerl. Scand., 4: 127-135.

Patrizi, G., and M. Poger 1967 The ultrastructure of the nuclear periphery. J. Ultrastruct. Res., 17: 127-136.

Ross, M. H., G . D. Pappas, J. T. Lanman and J. Lind 1958 Electron microscope observations on the endoplasmic reticulum in the human fetal adrenal. J. Biophys. Biochem. Cytol., 4:

Ryan, K. J. 1959 Biological aromatization of steroids. J. Biol. Chem., 234: 268-272.

Ryan, K. J., and 0. W. Smith 1965 Biogenesis of steroid hormones in the human ovary. Recent Prog. Hormone Res., 21: 367-402.

Schneider, W. C. 1959 Manometric Techniques. Ed. by W. W. Umbreit, R. H. Burris and J. P. Stauffer, Burgess Publ. Co., Minneapolis. Chap. 11.

Shikita, M., and B. Tamaoki 1965 Testosterone formation by subcellular particles of rat testes. Endocrinology, 76: 563-569.

Toren, D., K. M. J. Menon, E. Forchielli and R. I. Dorfman 1964 112 nitro enzymatic cleavage of the cholesterol side chain in rat testis preparations. Steroids, 3: 381-390.

Wilcox, R. B., and L. L. Engel 1965 The aromatization of 10-methyl and 10-hydroxymethyl steroids by human placental microsomes. Ste- roids, Suppl. 11, 249-255.

Yamada, E., and T. M. Ishikawa 1960 The fine structure of the corpus luteum in the mouse ovary as revealed by electron microscopy. Kyushu J. Med. Sci., 11: 235-259.

659-662.

PLATES

Abbreviations

ci, cytoplasmic invagination cis, cisternae ims, intranuclear membrane system inl, inner nuclear lamina 1, lipid ly, lysosome mf, myelin figure mit, mitochondrion n, nucleus nl, nucleolus

nP > onl,

rbc, rer, ser, tub, V, znl,

pm,

nuclear pore outer nuclear lamina plasma membrane red bood cell rough endoplasmic reticulum smooth endoplasmic reticulum tubules vacuole zonula nucleum limitans (electron dense zone)

PLATE 1

EXPLANATION OF FIGURE

1 This photomicrograph of sow corpus luteum includes portions of several lutein cells and a capillary. Note the size and extent of the smooth membranes (ser), and the numbers of mitochondria and lipid droplets. The smooth membranes seen here are excellent examples of the “fingerprint whorls” described in the text. Note also the mitochondria and lipid droplets trapped with the mass of s.e.r. at the upper right corner. x 5,600.

THE FINE STRUCTURE OF SOW LUTEIN CELLS Paul Goodman, John S. Latta, Richard B. Wilson and Barney Kadis

PLATE 1

85

PLATE 2

EXPLANATION OF FIGURES

2

3

This is an example of the “honeycomb” type smooth membrane system. x 21,000.

This combination of “honeycomb” and “fingerprint” system is the most frequently observed type of smooth membrane system. Note the continuity between the flattened cisternae and dilated tubules (arrow). x 35,000.


PLATE 2

87

PLATE 3

EXPLANATION O F FIGURES

4 These mitochondria demonstrate the tubular or tubulo-vesicular cristae of steroidogenic tissues (arrows). Note the many profiles of rough membranes (rer). x 35,000.

This is a small portion of the nucleus and adjacent cytoplasm of a sow lutein cell. The nuclear membrane is composed of outer and inner laminae (onl, inl) and an inner electron dense zone, the zonula nucleum limitans (znl), which are all fused at the nuclear pore (np) . The rough endoplasmic reticulum (rer ) is continuous with the smooth endoplasmic reticulum (*). x 56,000.

5

88


PLATE 3

89


EXPLANATION OF FIGURE

6 This sow lutein cell nucleus contains an extensive intranuclear smooth membrane system (ims). In addition this nucleus has a nucleolus (nl), a cytoplasmic invagination (ci), a membrane-bound body that contains a myelin figure (mf) and a lysosome-like structure (ly), some scattered smooth membranes (unlabeled arrows), a vacuole (v) and several lipid droplets (1). The nuclear membrane exhibits the same three- layered structure as the normal nucleus in figure 5. x 10,600.

PLATE 4

90

the fine structure of sow lutein cells

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