FINE STRUCTURAL CHANGES IN THE INTESTINAL EPITHELIUM OF THE BULLFROG DURING METAMORPHOSIS

The fine structural changes occurring in the columnar absorbing cells of the intestinal epithelium during metamorphosis of the bullfrog, Rana catesbeiana, have been examined by phase contrast and electron microscopy. Tissue samples taken just posterior to the entrance of the hepatopancreatic duct were fixed in veronal acetate-buffered osmium tetroxide and embedded in methacrylate. Under the action of the metamorphic stimulus (thyroid hormone), specific and characteristic responses were given by differentiated larval cells and undifferentiated basal cells within the same epithelium. The functional larval cells underwent degenerative changes and were retained for a time within the metamorphosing epithelium. Dense bodies appeared and increased in number in association with the loss of normal cell structure. Because of their morphology and time of formation, these bodies have been tentatively identified as lysosomes. Early in metamorphosis the basal cells did not change, but they subsequently proliferated to form a new cell layer beneath the remaining degenerating cells that lined the lumen. After the dying cells were sloughed into the gut, the new epithelium differentiated to form the adult tissue. The columnar epithelial cells of the mature animal differed in their fine structural organization from their larval precursors. Therefore, their adult configuration was molded by the action of the metamorphic stimulus.     

FINE STRUCTURAL CHANGES IN PROPLASTIDS DURING PHOTODESTRUCTION OF PIGMENTS

Etiolated bean leaves supplied δ-amino-levulinic acid in the dark synthesize large amounts of protochlorophyllide which is not converted to chlorophyllide upon illumination of the leaves. The fine structure of the proplastids is not affected by the treatment. When leaves containing "inactive" protochlorophyllide are exposed to light of 700 ft-c for 3 hours, they lose practically all their green pigments. During this period large stacks of closed membrane structures are built up in the region of the prolamellar body. These lamellar structures remain even when no or only traces of pigment are left in the leaves. In untreated control leaves the pigment content remained constant during similar illumination and the structural changes in the plastids consisted of a rearrangement of the vesicles from the prolamellar bodies into strands dispersed through the stroma; lamellae and grana formation occurred later.     

FINE STRUCTURAL CHANGES IN RESPONSE TO HORMONAL STIMULATION OF THE PERFUSED CANINE PANCREAS

The dog pancreas isolated in situ was perfused with oxygenated dog blood and stimulated with pancreozymin, secretin, or both. There were no significant changes in the fine structure of the acinar, centroacinar, or duct cells attributable to the perfusion. Combined glutaraldehyde and osmium fixation gave good preservation of the secretory products of the acinar cell. Before stimulation, the lumen of the acini is filled with material similar in texture to the content of the zymogen granules, but of somewhat lower density. Release of secretion commonly takes place by coalescence of the limiting membrane of zymogen granules with the plasmalemma, but one granule opening at the surface may frequently be joined by others coalescing with its membrane and forming an interconnected series all with contents having the same texture as the released zymogen. Such a mechanism seems to permit a more rapid release of secretory product than discharge of individual granules. Pancreozymin stimulation caused marked depletion of zymogen granules, but no obvious changes in the Golgi apparatus. It is clear, therefore, that this hormone exerts its effect upon release of granules rather than upon their formation. Secretin stimulation of water and bicarbonate secretion caused a marked washing out of the luminal contents, but had little detectable effect on cellular structure.     

THE FINE STRUCTURE OF ACOUSTIC GANGLIA IN THE RAT

Nerve cell bodies in the spiral and vestibular ganglia of the adult rat are surrounded by thin (about ten lamellae) myelin sheaths which differ in several respects from typical axonal myelin. In some instances lamellae surrounding perikarya appear as typical major dense lines, and in others as thin Schwann cell sheets in which cytoplasm persists. Discontinuities and irregularities appear in the structure of perikaryal myelin. Lamellae may terminate anywhere within the sheaths; they may bifurcate; they may reverse their direction; or they may merge with each other. The number of lamellae varies from one part of a sheath to another. In addition, the myelin of a single perikaryal sheath may receive contributions from more than one Schwann cell, which overlap and interleave with each other. The ganglion cells are of two types: those which are densely packed with the usual cytoplasmic organelles but have few neurofilaments (granular neurons), and those which exhibit large areas containing few organelles but have a high concentration of neurofilaments (filamented neurons). The latter cell type is ensheathed by myelin which is generally more compact that that surrounding the former. The formation and the physiologic significance of perikaryal myelin are discussed.     

肝癌细胞(AH_(66))甲胎蛋白基因结构的一些变化

对AFP基因重新表达的分子机制的研究,有助于了解癌变的本质。我们以AFPmRNA反转录合成的~3H-cDNA为探针,进行液相杂交;用RAF 65和RAF_(87)与体外染色质转录系统转录的~(32)P-RNA进行点杂交,测出移植性大鼠肝癌AH_(66)细胞核和离体染色质的AFP基因转录水平远远高于正常大鼠肝。以BamHI,EcoRI,HindⅢ和PstI酶解基因组DNA,然后与缺口翻译标记的~(32)P-RAF_(65)和~(32)P-RAF_(87)探针杂交,测知BamHI和EcoRI的酶谱相同,而HindⅢ和Pst I的带型明显不同,表明结构上存在某些变化。用HpaⅡ和MspI测定了AH_(66)和正常大鼠肝AFP基因的甲基化程度,结果表明,AH_(66)的AFP基因甲基化不足。AFP基因的染色质构型,由它对DNaseI的敏感性来测定,AH_(66)对DNaseI比正常大鼠肝更敏感,表明基因处于活性状态。所有这些结果表明,AH_(66)的AFP基因存在某些结构上的变化,这种变化对于AFP基因从掩盖到活性状态可能是重要的。     

THE GOLGI ZONE OF THE RAT SPERMATID AND ITS ROLE IN THE FORMATION OF CYTOPLASMIC VESICLES

Electron microscopic study of the Golgi zone of the rat spermatids revealed two main types of vesicular structures: flat vesicles generally accumulated in stacks and spheroidal vesicles of various sizes. The Golgi zone of young spermatids showed a predominance of flat vesicles and small spherical vesicles, while the "residual" Golgi zone of the maturing spermatids displayed an increased number of large spherical vesicles and thus became increasingly vacuolated in appearance. The images presented were suggestive of a transformation of the flat vesicles into spherical vesicles by fragmentation and dilatation and also of a passage of the spherical vesicles from the Golgi zone to the surrounding cytoplasm.     

THE FINE STRUCTURE OF THE PIGMENT EPITHELIUM IN THE ALBINO RAT

In this report, particular attention is paid to the inclusion bodies found in the apical cytoplasm of the pigment epithelial cell. These bodies are of variable size and form. The smallest (0.4 µ diameter) consist of a granular matrix enclosed by a single membrane, and are similar to the lysosomes of hepatic cells. Larger inclusion bodies contain areas of lamellated material in addition to granular matrix. The largest particles seen (2 µ diameter) are almost entirely lamellar. These different forms seem closely related, for it is possible to find all transitional stages between the smallest and largest particles. The relationship between the lamellar inclusion bodies and the rod outer segments is discussed.     

THE FINE STRUCTURE OF MITOSIS IN RAT THYMIC LYMPHOCYTES

The fine structure of rat thymic lymphocytes from early prophase to late telophase of mitosis is described, using material fixed at pH 7.3 either in 1 per cent OsO4 or in glutaraldehyde followed by 2 per cent OsO4. The structure of the centriolar complex of interphase thymocytes is analyzed and compared with that of centrioles during division. The appearance of daughter centrioles is the earliest clearly recognizable sign of prophase. Daughter centrioles probably retain a secondary relation to the primary centriole, while the latter appears to be related, both genetically and spatially, to the spindle apparatus. The nuclear envelope persists in recognizable form to help reconstitute the envelopes of the daughter nuclei. Ribosome bodies (dense aggregates of ribosomes) accumulate, beginning at late prophase, and are retained by the daughter cells. Cytokinesis proceeds by formation of a ribosome-free plate at the equator with a central plate of vesicles which may coalesce to form the new plasma membrane of the daughter cells. Stages in the formation of the midbody are illustrated.     

CHANGES IN POLYSOMES OF THE DEVELOPING RAT BRAIN

Abstract— Rat brain polysomes were prepared from a deoxycholate-treated postmito-chondrial supernatant in the presence of 2% bentonite and 1 mg/ml of yeast RNA to prevent partial degradation during preparation.

• 1 The polysomal preparations had an absorption maximum at 260 mμ and an absorption minimum at 235 mμ. The ratio of absorption maximum to minimum and the RNA to protein ratio were 1·58 and 1·06 respectively in 6-day-old rat brain polysomes. The sedimentation patterns showed six distinct peaks with sedimentation coefficients of 235S, 185S, 173S, 135S, 100S and 80S, indicating that these preparations have the characteristics of pure heavy polysomes.

• 2 The rate of [¹⁴C]phenylalanine incorporation into brain polysomal protein was maximal at approximately 10 days of age and decreased thereafter. A similar progressive reduction with increasing age was found in the stimulation of phenylalanine incorporation by the addition of 60 μg/tube of polyuridylic acid. However, the incorporation of phenylalanine into young rat brain polysomes was usually greater even with the addition of polyuridylic acid than in the older animals.

• 3 The comparative studies on sucrose density gradient centrifugation of polysomes between young and adult rat brains showed a considerable decrease of heavy polysomes in the older animals.

• 4 The effect of various factors on the stability of brain polysomes from both ages has been studied. The rates of RNA, protein and acid-soluble phosphorus release from polysomes of the adult rat brains were usually greater in the presence of high salt concentration, ethylenediaminetetra-acetic acid and urea than those from the corresponding preparations of younger animals. On the basis of evidence obtained from the above results it suggested that the adult brain polysomes were more unstable than those of younger animals.

• 5 The amount of polysomal RNA linearly increased up to the first 20 days after birth and then levelled off. The ratio of G + C/A + U of polysomal RNA was less in the young rat brains, falling to 1·30 as compared to 1·50 in older animals. The differences were statistically significant at less than a 1% level of confidence.

• 6 Polysomal preparations also contained RNase, phosphomonoesterase, phospho-diesterase and 5′-nucleotidase activities which cannot be washed off. The specific activities of these enzymes were generally higher in young rat brains than those in the adult.

     

THE FINE STRUCTURE OF OSTEOBLASTS IN THE METAPHYSIS OF THE TIBIA OF THE YOUNG RAT

The appearance of osteoblasts after fixation with OsO₄ is described in this paper. They have the basic structures found in other types of cells. The most striking feature is the array of rough-surfaced membranes of the endoplasmic reticulum; this feature is in keeping with the osteoblast's function of producing collagen as the bone grows. The sacs formed by these membranes probably represent the protein-containing granules described by other workers using the light microscope. They contain fine fibrillary material, and similar fibrils are to be found free in the cytoplasm. These fibrils could be tropocollagen units, although fibrils recognizable as collagen by their structure are found only outside the cell. The arrangement of the cell organelles does not seem to be related to the formation of collagen, but correlation of the fine structures of the cells with the histochemical and cytochemical findings in these cells reported by other workers leaves no doubt that they are directly concerned in the production of the organic matrix. It has not been possible to show that osteoblasts influence the passage of calcium or phosphate ions from the blood to the bone matrix.     

CHANGES OF THYMIDINE KINASE IN THE DEVELOPING RAT BRAIN

Abstract— Thymidine kinase (ATP: thymidine-5'-phosphotransferase EC 2.7.1.21) of the supernatant fraction from 6-day-old rat brain possessed a pH optimum of 8.0 and required the presence of 5mM-ATP and 2.5 mM-MgCl₂ for maximum activity. The activity was completely inhibited by addition of 1.8 mM-TTP. The enzyme activity was lost if the same supernatant fraction was refrozen and thawed. K_m was 2.8 × 10⁻⁶ M for [6-³H]thymidine.
Following subcellular fractionation of rat brain, the greatest proportion and highest specific activity of thymidine kinase was found in the supernatant fraction. Thymidine kinase activities reached a maximum at 6 days of age and then dropped sharply during maturation. Comparative studies of thymidine kinase activities of cerebrum, cerebellum and the remainder of the brain during growth indicated that the activity in the cerebellum was usually higher than those in the cerebrum and the remainder, and the biggest differences obtained at 6 days after birth corresponded with the peak in cerebellar activity.     

DEVELOPMENT OF FINE STRUCTURAL DAMAGE TO ALVEOLAR AND CAPILLARY LINING CELLS IN OXYGEN-POISONED RAT LUNGS

Rats were exposed to 98.5% oxygen at 765 torr for 6–72 hr. The pulmonary changes were investigated by electron microscopy and by morphometric methods. A progressive thickening of the air-blood barrier, from the normal 1.5 to 3 µ after 3 days, was due primarily to enlargement of the interstitial space by accumulation of edema which was replaced secondarily by cells and fibrin. This was accompanied by destruction of about 50% of the capillaries. Morphometric data allowed an estimate of the degree of impairment of lung function. The primary cellular damage was located in endothelial cells which underwent cytoplasmic changes and, finally, fragmentation. In contrast, the damage to the epithelial lining of alveoli was relatively scarce compared to the extensive endothelial changes. This pertained even to severely damaged lungs with 65% of the alveoli obliterated by a heterogeneous exudate. Possible causes for this apparently different reaction of epithelium (the first target cell) and endothelium to toxic oxygen effects are discussed.     

THE FINE STRUCTURE OF THE MID-BODY OF THE RAT ERYTHROBLAST

The development of the mid-body has been studied in mitotic erythroblasts of the rat bone marrow by means of thin sections examined with the electron microscope. A differentiated region on the continuous spindle fibers, consisting of a localized increase in density, is observed at the equatorial plane. The mid-body seems to develop by the aggregation of such denser lengths of spindle fiber. Its appearance precedes that of the cleavage furrow. A plate-like arrangement of fibrillary material lies transversely across the telophase intercellular bridge. Later, this material becomes amorphous and assumes the form of a dense ring closely applied to a ridge in the plasma membrane encircling the middle of the bridge. Although the mid-body forms in association with the spindle fibers, it is a structurally distinct part, and the changes which it undergoes are not shared by the rest of the bundle of continuous fibers.     

七星瓢虫精子鞭毛的超微结构(英文)

应用细胞整装制备和超薄切片技术,在透射电子显微镜下检查了七星瓢虫成熟精子鞭毛的超微结构。精子鞭毛是由一个典型的9＋9＋2轴丝,两个同形结晶的线粒体衍生物,两个附体（每个附体具有两部分,一个嗜锇致密月牙体和一个海绵月牙体）和一个非结晶体组成,在鞭毛终端部,仅存的轴丝失去了两个中央微管保留了9个具有动力蛋白臂的双微管和9个附微管。     

大鼠纹状体GABA受体的表达及年龄性变化

目的观察大鼠纹状体GABA受体的表达特征及增龄性变化。方法应用免疫组织化学及图像分析,Western blot观察大鼠纹状体GABARa受体的表达及年龄相关性变化。结果随着年龄的增加,大鼠纹状体GABAR阳性神经元及纤维明显增加,神经纤维排列紊乱,GABA免疫反应明显增强。结论老龄大鼠纹状体神经元GABAR的表达增加可能是一种有规律的增龄性变化。老年机体的某些抑制性精神症状可能与之有关。     

THE FINE STRUCTURE OF VON EBNER''S GLAND OF THE RAT

The fine structure of von Ebner's gland was studied in untreated rats and rats stimulated to secrete by fasting-refeeding or injection of pilocarpine. Cytological features were similar to those reported for pancreas and parotid gland. Abundant granular endoplasmic reticulum filled the basal portion of the cell, a well-developed Golgi complex was located in the vicinity of the nucleus, and the apical portion of the cell was filled with dense secretory granules. Dense heterogeneous bodies resembling lysosomes were closely associated with the Golgi complex. Coated vesicles were seen in the Golgi region and also in continuity with the cell membrane. Granule discharge occurred by fusion of the granule membrane with the cell membrane at the secretory surface. Successive fusion of adjacent granules to the previously fused granule formed a connected string of granules in the apical cytoplasm. Myoepithelial cells were present within the basement membrane, and nerve processes were seen adjacent to acinar and myoepithelial cells. Duct cells resembled the intercalated duct cells of the major salivary glands.