OBSERVATIONS ON THE FINE STRUCTURE OF LUTEIN CELLS : II. The Effects of Hypophysectomy and Mammotrophic Hormone in the Rat

Corpus luteum formation was induced in 26-day-old rats which were subsequently hypophysectomized and injected with mammotrophic hormone (MH, LTH). Sections of corpora lutea from these animals were examined with the electron microscope and compared with similarly prepared (Caulfield's fixed, Araldite embedded) corpora from normal pregnancy and from controls, the latter consisting of corpora prior to hypophysectomy and corpora from uninjected rats 7 to 14 days after hypophysectomy. Lutein cells from corpora lutea of injected animals and of normal pregnancy are characterized by abundant, tortuous, tubular agranular endoplasmic reticulum and by mitochondria, many of which are disc-shaped with dense matrices and both villiform and lamelliform cristae. The endoplasmic reticulum is most abundant in lutein cells from pregnant animals, in which cells it is in the form of thin, highly tortuous tubules. The form of the lipid droplets seen in cells of stimulated animals varies greatly. Marginal foldings of the lutein cells on the perivascular space were found in all instances. Lutein cells from hypophysectomized animals have a less highly developed agranular endoplasmic reticulum. The mitochondria have irregular outlines and a relatively lucid matrix. The lipid droplets in these cells show less tendency to be extracted, but are not so large or abundant as in the cells of onset controls. Granules believed to contain lipid pigments are common in the lutein cells of these control animals. It is suggested that lutein cells from corpora lutea which are actively secreting progesterone may be readily distinguished from lutein cells from non-active corpora by means of the multiple characteristics enumerated. It is further suggested that mammotrophic hormone has a general effect on the metabolism of lutein cells rather than solely affecting a specific organelle, the abundance or composition of which may be the limiting factor in the production of progesterone.     

The fine structure of the lutein cells in the mink (Mustela vison) with special reference to the secretory activity during pregnancy

Summary The ultrastructure of the lutein cells in the mink throughout pregnancy and the regression periodpost partum is described. To correlate the fine structure with the changes in the peripheral plasma progesterone levels, the concentrations of progesterone were measured by a rapid competitive protein-binding assay.Even during the delay period (e.g. as long the plasma progesterone levels remain at the basal level, <8ng/ml), the lutein cells in the mink exhibit structural criteria of functional activity. However, the increase in progesterone secretion is accompanied by some morphological transformations, characterized by the presence of more and more small dense homogenous bodies in the cytoplasm, which become irregular and scalloped during the stage with maximum release of progesterone. At this stage the agranular endoplasmic reticulum is often cisternal or vesicular.During the decline of the progesterone levels, typical and moderate electron-dense lipid droplets are found increasingly more within the lutein cells. The expanded agranular ER is now more sparse, while the granular ER becomes more pronounced, often forming parallel arrays. During this phase the mitochondria become elongated, dumb-bell, or cup shaped. After parturition the corpora lutea consist of cells in various stages of degeneration. At day 14post partum only a few lutein cells are still identifiable.Evidently the observed morphological changes take place in the lutein cells during the life span of corpora lutea. This feature lends further support to the concept that the mink lutein cells are steroid-producing cells and furthermore, that the corpora lutea may be the main sites of gestagen production during pregnancy.     

Structural changes in the granulosa lutein cells of pregnant cows between 60 and 245 days.

The structural changes in the granulosa lutein cells in the pregnant cows between 60 and 245 days, were observed. The polyhedral or pump cells has an acidophilic cytoplasm around the spherical nucleus. The glycogen granules increased in number up to 230 days of pregnancy. The lipid globules increased in size and amount during advanced pregnancy. The mitochondria showed a wide range of variations in shape and size. The matrix of many mitochondria contained dense inclusions which replaced the entire matrix in late pregnancy. The endoplasmic reticulum was chiefly of smooth type but a few stacks of the rough variety could be seen in the early days of pregnancy. Sometimes, whorls of smooth-surfaced endoplasmic reticulum enclosing mitochondria were seen. The Golgi complex was fully developed in the granulosa cells of all cases studied. The dense granules and lipid globules increased in size and number in the older corpora lutea. The cell surface showed numerous infolding of the plasma membrane.     

Fine structure of the corpus Luteum of the raccoon during pregnancy

Summary Ultrastructure of the granulosa lutein cells of the raccoon from throughout pregnancy has been described. The lutein cells often from epithelial cords which are separated by the connective tissues, capillaries and lymphatics. Based on the arrangements and modifications of the cytoplasmic organelles and inclusions, three types of lutein cells have been recognized. The type I lutein cells predominantly contain tubular, agranular endoplasmic reticulum, juxtanuclear Golgi complexes, a few round to rod-shaped mitochondria, some free ribosomes, and occasional lipid droplets. Occasionally the tubular cristae of mitochondria and tubular smooth endoplasmic reticulum appear contiguous. The type II cells contain abundant lace-like and/or stacked fenestrated endoplasmic reticulum cisternae that frequently form membranous whorls, some tubular, agranular endoplasmic reticulum, mitochondria, and lipid droplets. Mitochondria are usually small, but unusual large ones also occur. The small, rod-to round-shaped mitochondria usually have tubular cristae; but the large, oval, elongate, and cup shaped mitochondria possess tubular, lamellar, plate like, and whorl-like cristae. The plasma membranes of the cells are complexly elaborated and folded, especially when apposing each other. In favorable sections, strands of fenestrated cisternae appose the folds of the plasma membranes. In general, the amount of cytoplasmic organelles and inclusions vary greatly in the cells. The type III cells predominantly contain lipid droplets and sparse cytoplasmic organelles. The type I and II cells are found throughout pregnancy, but the type III cells are observed from mid gestation to term. The cytological features of type I and II cells suggest that they probably secrete most of the steroids, whereas the type III cells primarily store lipids.This research was supported by UPSHS grant AM-11376 and NIH contract 69-2136.     

Partial development of the steroidogenic ultrastructural features in degenerative corpora lutea after a single injection of pituitary extract in the Western painted turtle (Chrysemys picta)

Pituitary glands were removed from sexually mature female turtles (Chrysemys picta) and they were injected intraperitoneally (i.p.) into other mature females of the same species (experimental). In addition mature females of the same species received saline injection only (controls). Initially all the turtles used in this study were steroidogenically inactive with corpora lutea already undergoing luteolysis (degeneration) as these turtles had ovioposited their eggs approximately 2 weeks earlier. Forty-eight hour post injection the corpora lutea were removed from the control and experimental turtles. In the experimental turtles, the lutein granulosa cells developed ultrastructural features such as tubular and cisternal smooth endoplasmic reticulum (SER) and mitochondria with tubular cristae associated with lipid droplets. However, the controls maintained degenerative corpora lutea without steroidogenic ultrastructural features. The circulating progesterone (Pro) levels in the experimental turtles were significantly higher than the controls (P<0.049). Although the 48h development of steroidogenic ultrastructural features in the lutein granulosa cells was only partial in development, the effect of the pituitary taken from the inactive donor triggered an activating process within a short period, clear evidence of gonadotropic effect on the inactive corpora lutea. The present data offer interesting information on the short-term effect of gonadotropins during the non-reproductive period. This information may have useful implication under natural conditions particularly during the onset of a new reproductive cycle where the ovary is still inactive.     

The ultrastructure of the corpus luteum of the guinea-pig

Summary An electron-microscopic investigation, based on the suggestion that differences seen in progesterone levels under differing hormonal conditions might be reflected in the ultrastructural organisation of the lutein cells of the guinea-pig was undertaken. Comparisons were made between corpora lutea taken from animals during the normal oestrous cycle, pregnancy and lactation, and after hysterectomy or hypophysectomy.The lutein cells from the oestrous cycle corpus luteum appeared to be of two types, light and dark. The former were more numerous. The main difference between them lay in the arrangement of the endoplasmic reticulum. Lutein cells from corpora lutea (with the exception of the old degenerating corpora lutea) all contained well-developed agranular endoplasmic reticulum, little granular endoplasmic reticulum, several electron-dense lipid granules, lysosomal bodies which ranged from small spherical bodies to large autophagic vesicles and mitochondria. The mitochondria were numerous, and in the corpus luteum of pregnancy, they were closely associated with the parallel arrays of granular endoplasmic reticulum.With minor exceptions, the lutein cells of the guinea-pig present a strikingly uniform picture despite their hormonal condition.The manner in which this uniformity of ultrastructure may be related to observed differences in progesterone levels in the corpus luteum of the guinea-pig is discussed.Meat and Livestock Commission (MLC) Scholar.The authors wish to thank Dr. J. S. Perry for doing the surgery involved in this work and for the specimens of corpora lutea of hysterectomy. They are also grateful to him for his helpful discussions and interest throughout.     

OVARIAN STEROID CELLS : II. The Lutein Cell

The lutein cells of the rabbit exhibit fine structural variations during their life-span of 28 to 30 days. A systematic examination of the corpus luteum reveals that cellular distinctions may be recognized during the first, second, and third stages of pregnancy. The agranular endoplasmic reticulum reveals vesicular, tubular, and cisternal profiles after fixation with each of the following fixatives: glutaraldehyde, osmium tetroxide, and permanganate. The osmolality of the fixing solutions was varied with sucrose and recorded with an osmometer in order to determine the effect of osmotic concentration on the intracellular membranous profiles. It was determined that vesicles and short, branched tubules of similar structure are present in the agranular reticulum when the osmolalities are 300 to 800 milliosmols (iso-osmotic considered 300 milliosmols). At 900 milliosmols, the vesicular or tubular lumen is obliterated. Intracellular membrane profiles do not exhibit interconversions due to hyperosmotic fixative solutions. The agranular endoplasmic reticulum is randomly distributed as short tubular profiles during the first third of pregnancy. A continuity between these membranes and irregular, electron-opaque lipid masses is evident. When physiological and histochemical data indicate that the lutein cell may be storing sterol precursors, cytological observations show that the agranular endoplasmic reticulum exists in a more organized pattern within the cytoplasmic matrix. Vesicular and short tubular, circular aggregations as well as whorled cisternal patterns surround the larger, less electron-opaque lipid droplets. Surface views of cisternal agranular endoplasmic reticulum exhibit tubular extensions, accentuating the continuity between these two profiles. During the progress of pregnancy, the lutein cell increases in diameter, and accumulates both lipid inclusions and aggregations of intracellular membranes. The agranular endoplasmic reticulum may be peripherally packed and arranged parallel to the cell surface during later stages. In the postpartum, degenerating lutein cell, large myelin figures are present which form from the agranular endoplasmic reticulum. These cellular events are discussed in relation to lutein cell activity, including both secretion of product and storage of precursors.     

Structural characteristics of the corpus luteum during implantation in the rhesus monkey (Macaca mulatta)

Corpora lutea were obtained from ten pregnant rhesus monkeys during implantation, and the ultrastructure of granulosa and theca lutein cells was characterized. Specimens were individually staged with regard to the extent of implantation and the relationship to the rise in circulating progesterone and estrogen which is characteristic of early pregnancy. Structural changes characteristic of granulosa lutein cells occurring during implantation included: change in form of endoplasmic reticulum from predominantly agranular tubules to predominantly granular cisternae; reduction in size and number of lipid droplets; increase in area occupied by the Golgi and increase in length of the cisternae of the Golgi complex; development of numerous microvillus-lined intracellular spaces; increase in numbers of membrane-bound dense bodies including peroxisomelike bodies, multivesicular bodies within lobopodia, and other lysosomelike bodies; and alterations of mitochondrial cristae. These changes were suggestive of the production of a secretory protein, rapid utilization of existing steroid precursor reserves for the production of progesterone, and a reduction in capability for steroid precursor accumulation and processing by granulosa lutein cells. Structural changes characteristic of theca lutein cells occurring during implantation included an increase in size and number of lipid droplets, an increase in agranular endoplasmic reticulum, and an increase in area occupied by the Golgi complex. These changes were suggestive of an increased capability for steroid precursor accumulation and processing, perhaps for estrogen production, by the theca lutein cells.     

Electron cytochemical demonstration of four hydrolytic enzymes in the rat corpora lutea at second half of gestation

Corpora lutea from rat ovaries at mid pregnancy were fixed by perfusion and studied by electron cytochemistry for localisation of four hydrolytic enzymes. Using the metal-salt methods for acid phosphatase and aryl sulphatases activity was localised in small and large lysosomes, multivesicular bodies, Golgi complex and within cisternae of endoplasmic reticulum. The azo-dye coupling method for Beta-glucuronidase was less satisfactory and gave positive results in lysosomes, lipids and in the globules within the mitochondrial matrix. The latter two localisation were probably associated with affinity of the naphthol AS-BI for lipid material. In addition to plasma membranes, the reaction product for alkaline phosphatase with the lead-salt method was seen in lysosomelike bodies, in smooth endoplasmic reticulum and in occasional Golgi elements of granulosa lutein and endothelial cells. Increased activity of lysosomal acid hydrolases occurs when regressive changes of lutein cells start at the end of gestation and this might probably reflect the initiation of lytic processes.     

Electron cytochemical demonstration of four hydrolytic enzymes in the rat corpora lutea at second half of gestation

Summary Corpora lutea from rat ovaries at mid pregnancy were fixed by perfusion and studied by electron cytochemistry for localisation of four hydrolytic enzymes. Using the metal-salt methods for acid phosphatase and aryl sulphatases activity was localised in small and large lysosomes, multivesicular bodies, Golgi complex and within cisternae of endoplasmic reticulum. The azo-dye coupling method for Beta-glucuronidase was less satisfactory and gave positive results in lysosomes, lipids and in the globules within the mitochondrial matrix. The latter two localisation were probably associated with affinity of the naphthol AS-BI for lipid material. In addition to plasma membranes, the reaction product for alkaline phosphatase with the lead-salt method was seen in lysosomelike bodies, in smooth endoplasmic reticulum and in occasional Golgi elements of granulosa lutein and endothelial cells.Increased activity of lysosomal acid hydrolases occurs when regressive changes of lutein cells start at the end of gestation and this might probably reflect the initiation of lytic processes.     

SOME OBSERVATIONS ON THE FINE STRUCTURE OF THE LUTEIN CELLS OF X-IRRADIATED RAT OVARY

The ovaries of 10- to 13-week-old rats were exteriorized and irradiated with sterilizing doses of X-rays. Following treatment, the animals entered a phase of constant vaginal cornification. Animals were killed 8 to 12 wk after the onset of this phase, and their ovaries were prepared for electron microscopy. Tissue was fixed in glutaraldehyde, postfixed in osmium tetroxide (Millonig's, phosphate-buffered), and embedded in Epon. Lutein cells from these ovaries were compared with those from sham-irradiated controls. The cytoplasm of lutein cells from experimental animals was characterized by an increase in the amount of agranular endoplasmic reticulum and by an increase in the number of mitochondria. These mitochondria are more variable in external form and often possess increased numbers of villiform cristae. Other features noted were a decrease in the amount of cytoplasmic lipid granules and an increase in cell size and surface irregularity. The significance of the morphological findings is discussed in relation to ovarian hormone production in animals sterilized by X-irradiation.     

Feinstruktur der Luteinzellen des Meerschweincheneierstocks während der Schwangerschaft und des Zyklus

Zusammenfassung Die Feinstructur der Luteinzellen des Meerschweinchens während Schwangerschaft (15., 35., 45., 50., 55., 63. und 2 Tage nach der Geburt) und Zyklus (9, 14, 16, 20 Tage nach der Ovulation) wurden elektronenmikroskopisch untersucht. In den aktiven Luteinzellen kann man konzentrisch um die Lipoidtropfen angeordnete Strukturen des agranulären endoplasmatischen Retikulum beobachten, die später durch Membranstrukturen des granulären endoplasmatischen Retikulum ersetzt werden. Die Mitochondrien sind rund und enthalten tubuläre Innenstrukturen, die Lipoidtropfen sind elektronenoptisch dicht. Während der Rückbildung des Corpus luteum setzt sich das endoplasmatische Retikulum aus ungeordneten Vesikeln und Tubuli zusammen, die Mitochondrien sind länglich oder verzweigt, die Lipoidtropfen elektronenoptisch hell. Die Bedeutung dieser feinstrukturellen Veränderungen in der Luteinzelle wird diskutiert.

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The ultrastructure of lutein cells in the guinea pig corpus luteum during pregnancy and oestrous cycle

Summary The fine structure of the lutein cells in guinea pigs corpora lutea of pregnancy (15th, 35th, 45th, 50th, 55th, 63th day and 2 days after birth) and during oestrous cycle (9, 14, 16, 20 days after ovulation) is described. During the active phase of the corpus luteum the formation of concentric whorls of agranular endoplasmic reticulum around lipid droplets is observed, but later the granular endoplasmic reticulum increases. In this stadium the mitochondria are round with tubulous cristae and the lipid droplets are increased in density. During the involution of the corpus luteum the endoplasmic reticulum does not form concentric whorls, the mitochondria are elongated, polymorphic, the lipid droplets have lower electron density. These ultrastructural changes in the lutein cells are discussed concerning the role of the cell organelles in the steroid synthesis.

Diese Arbeit wurde mit Unterstützung durch die Alexander von Humboldt Stiftung durchgeführt.     

THE DIFFERENTIATION OF WHITE ADIPOSE CELLS : An Electron Microscope Study

Differentiating white adipose tissue from presumptive and developing fat pads of newborn and young rats was fixed in buffered osmium tetroxide, embedded in Vestopal W, and examined in an electron microscope. Pre-adipose cells were found to be fibroblasts characterized by their spindle shape, long tenuous cytoplasmic extensions, and profuse endoplasmic reticulum. The developmental stages traced from fibroblast to mature adipose cell show a gradual change in cell shape, an accumulation of cytoplasm and non-membrane-bounded lipid, a decrease in the endoplasmic reticulum, and a change in shape of mitochondria. Transitory glycogen appears at mid-differentiation. Numerous smooth-membraned vesicles occur in the cytoplasm throughout differentiation. Pinocytosis is constantly evident. Cells of the multilocular stage are shown to differ from brown fat cells, particularly with respect to cytoplasmic membrane systems and mitochondria. No transport of particulate lipid from the lumen of the capillary to, or within, the adipose cell was detected, nor could any cell organelle be demonstrated to be visibly related to lipid synthesis and/or deposition.     

Organelle distribution in chick neuroepithelial cells: effects of colchicine and cytochalasin B

The intracellular distribution of mitochondria, cytoplasmic inclusions and rough endoplasmic reticulum cisternae of chick neuroepithelial cells was investigated at neurulation stages 6, 8, 10 and 12. These neuroepithelial cells were subdivided into three zones: apical, median and basal and the distribution percentages of distribution of these organelles were obtained. Mitochondrial distribution was related to the energy supply that mitochondria provide for apical microfilament contraction. Cytoplasmic inclusions were distributed preferentially in the apical zone of the neuroepithelial cells during the four stages. Rough endoplasmic reticulum cisternae were homogeneously distributed in the three zones at stages 10 and 12, but at stages 6 and 8 there are more elevated percentages of rough endoplasmic reticulum in the apical zones than in the other zones. Experimental treatments with colchicine and cytochalasin B does not modify the patterns of mitochondria and rough endoplasmic reticulum cisternae but alters the distribution of cytoplasmic inclusions. Finally, there is a correlation in the normal neurulating neuroepithelial cells between the distributions of mitochondria and rough endoplasmic reticulum distribution and between the distributions of mitochondria and cytoplasmic inclusions distribution. This relationship is retained in the treated neuroepithelial cells.     

Ultrastructural changes in granulosa lutein cells and progesterone levels during preimplantation,implantation, and early placentation in the western spotted skunk

Summary The ultrastructure of corpora lutea obtained during the preimplantation, implantation and early postimplantation periods has been studied in 20 western spotted skunks. Fine structure of granulosa lutein cells was correlated with progesterone levels. The corpus luteum of the prolonged (7 month) preimplantation period contained undifferentiated small granulosa cells and differentiated large granulosa lutein cells. The former ranged in size between 12 and 20 and the latter between 20 and 45 . The ratio of small and large cells was about equal in an animal 2 days prior to nidation whereas only few small cells and numerous large cells were observed in an animal estimated to be 8 to 12 hours from nidation. Occasionally small cells were observed amidst large ones during the 24 hour nidation period, i.e. adhesion of trophoblast with the luminal uterine epithelium, but small cells were absent in animals after this period. Small cells had some smooth and rough endoplasmic reticulum, rod-shaped mitochondria with platelike cristae, small Golgi complex, and relatively smooth plasma membranes. Large lutein cells had abundant smooth endoplasmic reticulum, membranous whorls of smooth endoplasmic reticulum, usually round mitochondria with tubular and lamellar cristae, a well developed Golgi complex, variable amounts of lipid droplets, and highly plicated and ruffled plasma membranes. Peripheral plasma progesterone levels during the prolonged preimplantation period ranged between 1.1 and 7.9 ng/ml, but during implantation it was between 8 and 16.6 ng/ml. It is suggested that plasma progesterone levels fluctuate during the time of implantation and should not be regarded as a basis to predict actual nidation in the western spotted skunk.This research was supported in part by Grant Number HD06556 from the National Institute of Child Health and Human Development.     

Organelle differentiation in the chick blastoderm during hypoblast formation

Summary The ultrastructure of the chick blastoderm was examined at three developmental stages, from an unincubated single-layered system through hypoblast advancement to full hypoblast formation.With the onset of incubation the nucleolus changes from a loose network of intermingled pars fibrosa and pars granulosa into a compact body with a definite matrix material.The endoplasmic reticulum, mitochondria, and Golgi complex increase in complexity and volume. In blastoderms with a fully developed hypoblast a special asymmetrical endoplasmic reticulum becomes abundant. These data are analysed in relation to similar structural differentiation of the nucleolus, endoplasmic reticulum, Golgi complex and mitochondria in the embryonic development of other vertebrate groups.The above changes in organelle structure are noted in both the epi- and the hypoblast, although these organelles become more abundant in the former. In the intermediate stage no differences are noted between epiblast cells underlined by hypoblast and those of the anterior single-layered region. The above changes in the epiblast must therefore be related to age and not to contact with the advancing hypoblast.Previous studies mentioned in the text seem to indicate that the inducing effect of the hypoblast on the epiblast is exerted after its complete formation and not during its advancement. Our results in the organelle differentiation during hypoblast formation are in accordance with this hypothesis.     

Organization of the endoplasmic reticulum in renal cell lines MDCK and LLC-PK1

The spatial organization of the endoplasmic reticulum has been studied in two renal cell lines, MDCK and LLC-PK1, which originate from the distal and proximal portions of the mammalian nephron, respectively, and which form a polarized epithelium when they reach confluence in tissue culture. The two renal cell lines, grown to confluence on either solid or permeable supports, were investigated by fluorescence microscopy, confocal microscopy, and transmission electron microscopy. Fluorescence labeling of the endoplasmic reticulum was achieved using the cationic fluorescent dye DIOC₆ (3). In order to differentiate fluorescent labeling of the endoplasmic reticulum from that of the mitochondria, cells were also labeled with rhodamine 123. For electron microscopy, the spatial organization of the endoplasmic reticulum was examined in thick sections using the long-duration osmium impregnation technique or the ferrocyanide/osmium technique. In both cell lines, the endoplasmic reticulum formed an abundant tubular network of canaliculi that frequently abutted the basolateral domain of the plasma membrane and occasionally the apical membrane. Elements of the endoplasmic reticulum were also found in close proximity to mitochondria that, as in the nephron, formed branched structures. Canaliculi appeared circular or flattened and had an inner diameter of 10–70 nm for MDCK cells and 20–90 nm for LLC-PK1 cells. Such a three-dimensional organization might facilitate the translocation of defined lipid species between the endoplasmic reticulum and the plasma membrane, and between the endoplasmic reticulum and mitochondria.     

Ultrastructural characteristics of insect corpora allata in relation to larval diapause

Summary The ultrastructure of active and inactive corpora allata from last instar larvae of the southwestern corn borer, Diatraea grandiosella, was examined. Active glands were obtained from pre-, early, and mid-diapausing larvae; inactive ones from late and non-diapausing larvae. Each gland contains 13 to 18 cells which have the following common features: well developed smooth endoplasmic reticulum, scattered rough endoplasmic reticulum and free ribosomes, microtubules, vacuolated nucleoli, and interlocking plasma membranes. The gland contains intercellular deposits, and is supplied by regular and neurosecretory axons.Special ultrastructural features of the corpus allatum from the five groups of larvae examined were as follows: pre-diapause: extensive vesicular smooth endoplasmic reticulum, numerous cup-shaped mitochondria and Golgi bodies with stacked cisterns and vesicles, few small lipid droplets, large nuclei with dispersed chromatin, absence of lysosomes; early diapause: stacked, whorled, and vesicular smooth endoplasmic reticulum of equal abundance, numerous rod-shaped mitochondria, some Golgi bodies but without distinct stacks of cisterns, few lipid droplets and lysosomes, chromatin dispersed and also attached to the nuclear envelope; mid-diapause: similar to early diapause except for the presence of more stacked, smooth endoplasmic reticulum, chromatin in large chunks mostly attached to the nuclear envelope; late diapause: whorled smooth endoplasmic reticulum and rod-shaped mitochondria predominating, complicated Golgi bodies with stacks of cisterns and large empty sacs, few large lipid droplets, some lysosomes containing mainly whorled bodies, chromatin in large chunks attached to the nuclear envelope; non-diapause: similar to late diapause except for less extensive smooth endoplasmic reticulum, more abundant mitochondria, fewer intercellular deposits. Although these observations suggest that the smooth endoplasmic reticulum, and possibly mitochondria, and Golgi bodies are involved in juvenile hormone production, specific sites of synthesis or storage of the hormone were not revealed.Supported in part by grant no. PCM 74-18155 A01 from the National Science Foundation. Contribution from the Missouri Agricultural Experiment Station as journal series no. 8234. We thank Ms. L. Yin for her skillful assistance, and Dr. M.F. Brown of the College of Agriculture Electron Microscope Facility for his advice and the use of equipment.     

Ultrastructure of the indifferent gonad in male and female pig embryos.

Pig embryos aged 24 days were obtained from artifically inseminated sows for ultrastructural study of the indifferent gonads. Sex was identified by chromosome analysis. The gonads are composed in both sexes of three different tissues: the surface epithelium, the gonadal blastema and the mesenchyme. The surface epithelial cells contained elongate mitochondria, granular endoplasmic reticulum, free polysomes, the Golgi complex, fine filaments and coated vesicles. The primitive cords were continuous with the surface epithelium and the interior of the gonad was occupied by blastema cells. They had prominent nucleoli, elongate mitochondria, granular endoplasmic reticulum, the Golgi complex, free polysomes, some lipid droplets and occasionally circular smooth membrane profiles resembling the agranular endoplasmic reticulum. Individual primordial germ cells were seen in all parts of the gonad. They were roundish with prominent nucleoli, globular mitochondria, granular endoplasmic reticulum, free polysomes, the Golgi complex, coated vesicles, lipid droplets and dense bodies. Degenerating cells and cells having pseudopods were also encountered. In comparison to the gonad at the age of 22 days, the primordium had grown into a longitudinal roundish protrusion and the number of primoridal germ cells had increased. Histological and ultrastructural observations showed that the pig gonads at the age of 24 days were similar in both sexes.     

Continuities between mitochondria and endoplasmic reticulum in the mammalian ovary

Summary An electron microscope study of developing mouse oocytes has revealed a close morphological relationship between mitochondria and endoplasmic reticulum. In many instances, it was noted that the outer mitochondrial membrane was continuous with the reticular membranes. These cytoplasmic membranes are smooth or studded with ribosomes. These continuities establish an open channel between the endoplasmic reticulum and mitochondria. Similar connections are also found in isolated preparations of mitochondria from the adult guinea pig ovary. The functional significance of these observations are discussed in relation to biochemical studies which demonstrate a transfer of protein from endoplasmic reticulum to mitochondria.