Ultrastructural morphogenesis and functional differentiation of the dogfish thyroid follicle (author's transl)

From the 20 mm stage, in the cells of the dogfish embryo thyroid, some Golgi vesicles get the ability to trap iodine. At subsequent stages, electrondense intracytoplasmic cavities with microvilli are observed in the Golgi field; their membranes also trap iodine. These cavities increase in volume, draw toward the cellular periphery and export their contents in an intercellular space previously limited by tight junctions. The same events occur in several adjacent cells, which constitute the first follicular lumen. The last stage of follicular individualization is basement membrane formation. Arguments are given which support the hypothesis of the Golgi origin of intracytoplasmic cavities with microvilli. Iodine organification just as thyroid hormones synthesis and secretion occur at 25 mm stage, when cells are not grouped in follicle. It is concluded that cells containing intracytoplasmic cavities with microvilli are fully functional units.     

The relationship between the folliculo-stellate network and the thyrotropic cells of the avian adenohypophysis

Summary The folliculo-stellate network of the avian adenohypophysis consists of stellate cells surrounding colloid-containing follicular cavities into which cilia and microvilli project. Other identifying criteria are agranularity, junctional complexes at the apical pole, presence of cytoplasmic processes ramifying between adjacent secretory cells, and close appositions of plasma membranes linking folliculo-stellate cells and presumptive thyrotropic cells.Transmission electron microscopy reveals that TRH and L-DOPA induce simultaneous ultrastructural changes in the folliculo-stellate network and in the thyrotropic cells. TRH transforms at cell of the cephalic lobe into a highly hypertrophic cell in which enlargement of cisterns of rough endoplasmic reticulum containing secretory granules, development of a large Golgi complex, presence of newly synthesized secretory granules, and granulation of the cytoplasm are the main features. In the meantime, the follicular cavities become dilated by large amounts of homogeneous colloid. The administration of L-DOPA also leads to the development of dilated cisterns in presumptive thyrotropic cells of the cephalic lobe. Intracisternal granules, immature secretory granules, and large Golgi complexes, however, are not observed. Degranulation of the cytoplasm is obvious. The follicular cavities of both cephalic and caudal lobes are enlarged and filled with colloid in which granular elements are noted.The ultrastructural changes observed in thyrotropic cells and in the folliculo-stellate network reflect functional changes induced by the experimental manipulation. These changes may be related, directly or indirectly, or completely independent.     

Follicles in the Endocrine Pancreas of Myxine glutinosa Studied by Scanning Electron Microscopy

Abstract Scanning electron microscopic studies of the inner surfaces of the follicular cavities in the endocrine pancreas of Myxine glutinosa have revealed two types of follicles. The predominant type of follicles is lined by cells bearing microvilli, while the rare second type has smooth surfaced cavities. It is postulated, that the microvillous cells absorb material stored in these follicles, while the smooth surfaced follicles are disintegrating.     

Ultrastructural pathology of the thyroid folliculo-papillary and follicular carcinoma

Twenty cases of thyroid carcinoma (10 follicular and 10 folliculo-papillary) were ultrastructurally studied. In the follicular carcinoma the most striking features were: microfollicular cavities with microvilli from the apical surface of the tumorous cells, intracellular microlumens, swollen mitochondria sometimes containing electrondense bodies and tightly packed filaments. In the solid sheaths light and dark cells were present. Golgi complexes were disposed in small dense cristae. The nuclei were large, round, oval or with a folded appearance. In the folliculo-papillary carcinoma were found nuclei with an irregular shape containing stage I and stage II inclusions, dilated endoplasmic sacks, closely packed, sometimes dystrophic mitochondria, dense bodies or tightly packed parallel filaments and numerous phagolysosomes. The peroxidase activity wa present as black precipitates in the nuclear envelope or around colloid droplets. The acid phosphatase activity was found as unhomogeneous precipitates inside the lysosomes. From this study it could be concluded that the follicular and folliculo-papillary carcinomas have some common ultrastructural features; the ultrastructural and cytoenzymological patterns suggest marked alteration of the synthesis, storage and secretion of thyroid hormones.     

TSH stimulation of iodine organification in early foetal rat thyroid in vitro

Thyroid glands from 15 day-old rat foetuses were incubated in Eagle's medium containing Na 125I and supplemented, or not, with TSH for 4 or 24 hours. Electron microscopic radioautographic study shows silver grains mainly in follicular cavities only in the thyroids submitted to TSH during 24 hr. A functional differentiation must therefore take place in thyroid cells under TSH stimulation.     

Occurrence of colloid-containing follicles and ciliated cysts in the hypophysial pars tuberalis from guinea pigs of various ages

Colloid-containing follicles and ciliated cysts in the hypophysial pars tuberalis of guinea pigs at various ages ranging from 5 days to 36 months were examined by periodic acid-Schiff (PAS) reaction, immunohistochemistry, and electron microscopy. The follicles storing PAS-positive colloid were encountered in the pars tuberalis of all guinea pigs examined, although only a few were present in young animals. The follicles gradually increased in number with age. The largest number of follicles was found in the senile male group: 141.3 +/- 11.9, about 10 times the number in the 5-day-old male group. The follicles were scattered throughout the entire length of the pars tuberalis. Follicles with enlarged luminal cavities were concentrated in the ventral caudal region surrounding the infundibular stem and merges with the pars distalis. Three different types of follicles were found by electron microscopy: 1) those surrounded by nongranulated follicular cells that may correspond to the stellate-follicular cells in the pars distalis, 2) those surrounded by specific cells that were packed with vesicular inclusions, and 3) those surrounded by granulated cells that may be gonadotropes. In the follicles lined by non-granulated follicular cells, long, prominent microvilli and cytoplasmic processes protruding into the lumen and invaginations of colloid were often observed at the apical cell region. The follicles lined by the specific cells having numerous vesicles were localized only in the ventral caudal portion. The vesicles ranged from 200 to 700 nm in diameter, and the outer surface of their limiting membrane was partly studded with ribosomes. Gonadotropes immunoreactive to the luteinizing hormone (LH) and follicle-stimulating hormone (FSH) antisera were distributed in the guinea pig pars tuberalis. As well as the typical follicles described above, the follicles composed solely of granulated cells showed microvilli protruding into the cavities and junctional complexes at the apical lateral surface. They stored heterogeneous materials in the lumina. Some secretory granules gave the appearance of being discharged into the lumen. Ciliated cysts were frequently observed in the pars tuberalis; their incidence was 71.7%. The ciliated cysts were much larger than colloid-containing follicles. Cystic cavities were only partly filled with heterogeneous materials showing colloid-like, flocculent, and granular features.     

Vitellogenin transcytosis in follicular cells of the honeybee <Emphasis Type="Italic">Apis mellifera</Emphasis> and the wasp <Emphasis Type="Italic">Polistes simillimus</Emphasis>

Vitellogenin receptor (VgR) is a low-density lipoprotein receptor responsible for the mediated endocytosis of vitellogenin (Vg) during egg formation in insects. The maturing oocyte is enveloped by a follicular epithelium, which has large intercellular spaces during Vg accumulation (patency). However, Vg has been reported in the cytoplasm of follicular cells, indicating that there may be a transcellular route for its transport. This study verified the presence of VgR in the follicular cells of the ovaries of the honeybee Apis mellifera and the wasp Polistes simillimus in order to evaluate if Vg is transported via transcytosis in these insects. Antibodies specific for vitellogenin receptor (anti-VgR), vitellogenin (anti-Vg), and clathrin (anti-Clt) were used for immunolocalization. The results showed the presence of VgR on the apical and basal plasma membranes of follicular cells of the vitellogenic follicles in both species, indicating that VgR may have been transported from the basal to the apical cell domain, followed by its release into the perivitelline space, evidenced by the presence of apical plasma membrane projections containing VgR. Co-localization proved that Vg bind to VgR and that the transport of this protein is mediated by clathrin. These data suggest that, in these social insects, Vg is transported via clathrin-mediated VgR transcytosis in follicular cells.     

An analysis of the ultrastructure of epithelial cells of the rat proximal tubule at early stages of penicillin elimination

A study was made of the ultrastructure of epithelial cells of the rat proximal tubules nephrons 25-30 seconds, and 15 and 30 minutes following penicillin injection. The morphological changes in the transporting cells that were observed involved the dilation of the inner cavities of canals and cisterns of the endoplasmic reticulum. The number of elements of the smooth endoplasmic reticulum concentrated on the periphery of the cell, near the basolateral border, was seen to increase. Microbodies appeared enlarged with the appearance of the nucleolus; the electron density of the cytoplasmic ground substance fell down. The space between cells augmented, and the interstitial space between infoldings of the basal plasmalemma was much broadened. Similar morphological changes but different in the intensity were found at either stage examined. The maximum changes were established 25-30 seconds following penicillin injection.     

Thyroid follicular morphogenesis mechanism: organ culture of the fetal gland as an experimental approach

The morphological and physiological changes induced by organ culture and thyroid-stimulating hormone (TSH) stimulation in the rat fetal thyroid gland were studied. Organ culture increased Golgi activity which was further enhanced by TSH, subsequently facilitating the formation of intracellular lumina. TSH also raised the intracellular cAMP level. The intracellular lumina observed during follicular morphogenesis are structurally comparable to typical intracellular cavities formed in adult thyroid cells, which are considered as being the result of increased Golgi activity. The intracellular lumen, therefore, is probably not a physiologically significant step in thyroid morphogenesis.     

LH, FSH, PRL and ACTH cells in pituitary glands of cows with ovarian cysts

We investigated morphometrically and densitometrically LH, FSH, PRL, and ACTH cells in pituitary glands in cows with follicular cysts and normal animals. Three groups were considered: cows in diestrus, cows in periestrus and cows with follicular cysts. The periestrous group was obtained by merging pro- and metaestrous groups, since the two did not differ when evaluated separately. The attribution to groups was confirmed by plasma progesterone measurements and by postmortem examination of the ovaries. After immunocytochemical labeling the pituitary cells were counted, and their area and total immunoreactivity were measured. The results suggest hypofunction of the LH cells (P < 0.05) and hyperfunction of the ACTH cells (P < 0.05) from the cows of the follicular cyst group. The FSH and PRL cells were similar in the three groups. These changes are consistent with the reduced LH release reported by most authors in cows with follicular cysts and should be relevant to the pathogenesis of the bovine follicular cysts. The subnormal activity of LH cells might be secondary to the activation of the ACTH cells.     

Fluctuations in follicular structures of rat thyroid glands during 24 hours: fine structural and morphometric studies

The thyroid follicles of adult male Wistar rats were examined at six evenly spaced times over 24 hr with a morphometric technique. Follicular structures were subjected to distinct variations during 24 hr, with respect to volume and numerical densities of follicles in the thyroid gland, and diameters, volumes, cell numbers, and luminal surface areas of individual follicles. Variations in follicular structures were divided into two phases: a large follicular phase at 1200, 1600, and 2000 hr and a small follicular phase at the other times. Although volume densities of follicles in the gland varied with a small amplitude, diameters, volumes, and cell numbers of individual follicles exhibited distinct fluctuations during 24 hr. Numerical densities of follicles in the gland changed distinctly during the small follicular phase as well. Degenerating follicular cells appeared in the follicular lumen especially at 1600 hr. No mitotic follicular cells were found throughout the experiment. Furthermore, one to three follicular cells of two adjacent follicles were often in contact with each other at 0400, 0800, and 1200 hr, and these follicles were lined by the common basement membranes. These results suggest that the variations in follicular structures during the small follicular phase occur in the form of follicle separation and fusion. Moreover, the morphological and morphometric variations in follicles reflect those in subcellular structures of follicular cells previously reported by us.     

Increased velocity and induction of chemotactic response in mouse spermatozoa by follicular and oviductal fluids.

The dynamic parameters of mouse sperm cells exposed to follicular and oviductal fluids were assessed. Spermatozoa were tracked on a chemotactic Zigmond chamber and recorded using a videomicroscopy system. The results were evaluated with computer-supported image analysis. Follicular fluid at a dilution of 10(-4) markedly increased the proportion of spermatozoa with high velocity, and stimulated chemotactic behaviour. The highest velocities were observed in sperm cells exposed to oviductal fluid, and a greater proportion of these cells had high velocity compared with those exposed to follicular fluid. Chemotaxis was induced in spermatozoa exposed to oviductal fluid at dilutions of 10(-3) and 10(-5). These results suggest the presence of temporal subpopulations of responsive spermatozoa, considering the distance travelled towards both follicular and oviductal fluids and the proportion of sperm cells migrating towards the gradient in the highest distance ranges. This is the first report on the effect of isolated follicular and oviductal fluids on dynamic parameters and chemotaxis of mouse spermatozoa. The findings support previous work showing that the motility and directionality of mouse sperm cells is increased by factors in the microenvironment of the egg. Although the significance of these factors in vivo is unknown, it is possible that there is a relay mechanism involving sequential activity of both oviductal and follicular fluids to direct the male gametes towards the egg.     

Post-hatching evolution of the pineal gland of the chicken

The authors studied the evolution of the pineal gland of the chicken (Gallus gallus) from hatching until 34 months of age. They describe the progressive decrease of the follicular cavities and the appearance of solid-looking cavities. The stroma increases with age, dividing the pineal parenchyma into territories of small caliber.     

Differentiation and diversification of follicular cells in polytrophic ovaries of crane flies (Diptera: Nematocera: Tipulomorpha and Trichoceridae)

To gain insight into the evolution of differentiation pathways that are involved in the follicular cells' morphogenesis in dipteran ovaries we have undertaken the comparative morphological analysis of the follicular cell behavior in crane flies, representatives of more ancestral nematocerous flies. This analysis revealed that initially the organization of the follicular epithelium in the species under study shows significant similarities to that reported in the ovaries of true flies (Brachycera), indicating that the ancestors of dipterans must have evolved a common and specific system of the early patterning of their follicular epithelium. On the other hand, in contrast to Drosophila and other advanced brachycerans, the follicular cells in the studied nematoceran ovaries do not exhibit any migratory activity. Instead, they were found to change their relative position but only within the epithelial layer. These "translocations" appeared to depend merely on cell shape changes. Although the "immobility" of the follicular cells in the ovaries of crane flies results in the lower number of their specialized subgroups when compared with the true flies, the functional homology between particular subsets of follicular cells can be postulated. We suggest that the anterior polar cells and the micropyle forming anterior terminal follicular cells in crane fly ovaries have their counterparts in the brachyceran anterior polar cells and border cells, respectively.     

Pituitary cytology of the chimaeroid fish Hydrolagus colliei (Lay and Bennett).

The pituitary of Hydrolagus colliei is divided into the adenohypophysis, neurohypophysis and an oral Rachendachhypophyse. The adenohypophysis is further divided into rostral and proximal pars distalis and neurointermediate lobe. The neurohypophysis is restricted to the pars intermedia only. The rostral pars distalis is composed of acidophils, chromophobes, lightly PAS+ cells and amphiphils. The amphiphils were stained with Heidenhain's iron haematoxylin and lead haematoxylin also. The proximal pars distalis is formed of cyanophils where the granules are AF and PAS positive, acidophils, chromophobes and H.Pb+ cells. The pars intermedia has perviascular amphiphils which are H.Pb+, lightly PAS+ cells and chromophobes. Few AF+ cells were also identified. All the component parts of the adenohypophysis have follicular cavities which are probably developed from the hypophysial cavity, which is well seen in the young specimen as a single cavity extending antero-posteriorly throughout the adenohypophysis.     

Structural and functional diversification of follicular epithelium in Coreus marginatus (Coreidae: Heteroptera)

Follicular cells in Coreus marginatus are diversified into two main subpopulations of different cell morphology, ultrastructure, distribution of F-actin and ionic communication between oocyte and follicular cells. Cells forming the insert between the operculum and the bottom of the egg envelope and, subsequently, a circle of micropylar processes were retarded as compared to the developmental advancement of follicular cells in the equatorial part of ovarian follicle. Pinocytotic and vitellogenic activity in the ooplasm adjoining the insert cells were lower than in other regions. The inhibition of vitellogenesis in the neighbourhood of insert cells, which were not in ionic contact with the ooplasm, supports the hypothesis that there is a relation between follicular cell development and the regional intensity of vitellogenesis in heteropteran ovarian follicles.     

Alterations within the rat thyroid gland during vitamin A deficiency

Thyroid glands from female rats kept vitamin A deficient for one, two, and three months were examined by electron microscopy. After one month on the diet, no consistent alterations were noted. After two months, the colloid in some follicles displayed a peripheral zone of decreased density. In addition, ultimobranchial follicles within the gland had become keratinized. After two to three months on the diet, cells were seen entering the colloid. Many of these cells were identified as follicular cells since they often occurred in groups and occasionally exhibited remnants of desmosomes. Often the cells within the colloid appeared vacuolated, and by light microscopy were thought to contain lipid. However, electron microscopy revealed that these cells contained many digestive vacuoles rather than lipid droplets. Quantitative and autoradiographic studies indicated that thyroids of vitamin A deficient rats took up less radioiodide than thyroids of control rats. The keratinization of ultimorbranchial follicles in vitamin-A deficiency has been suggested as preliminary in the histogenesis of squamous cell carcinoma. However, an effect of vitamin A deficiency on thyroid follicular cells has not heretofore been reported. It's possible that the presence of follicular cells in the colloid reflects an accelerated turnover of these cells and could indicate an early pathological sign.     

Clearance and fate of leukemia-inhibitory factor (LIF) after injection into mice

Leukemia-inhibitory factor (LIF) elicits effects on a broad range of cell types, including cells of the monocytic and megakaryocytic series, embryonal stem cells, hepatocytes, adipocytes, and osteoblasts. Native and recombinant LIF, injected intravenously into adult mice, had an initial half-life of 6-8 min and a more prolonged second clearance phase. Clearance of 125I-LIF from the circulation was paralleled by a rapid accumulation in the kidneys, liver, lungs, and spleen and a more gradual accumulation in the thyroid gland. Labeling of the renal glomerular tufts, parenchymal hepatocytes, splenic red pulp, alveolar pneumocytes, and thyroid follicular cells as well as of megakaryocytes and osteoblasts in the bone cavities, placental trophoblasts, and cells of the choroid plexus was demonstrable autoradiographically. The appearance of a large amount of nonprecipitable 125I in the urine suggested that the kidneys were the major route of LIF clearance from the body.