Read-through transcription of tRNA underlies the cell cycle-dependent dissociation of IHF from the DnaA-inactivating sequence datA

Timely initiation of chromosomal DNA replication in Escherichia coli is achieved by cell cycle-coordinated regulation of the replication origin, oriC, and the replication initiator, ATP-DnaA. Cellular levels of ATP-DnaA increase and peak at the time for initiation at oriC, after which hydrolysis of DnaA-bound ATP causes those to fall, yielding initiation-inactive ADP-DnaA. This hydrolysis is facilitated by the chromosomal locus datA located downstream of the tRNA-Gly (glyV-X-Y) operon, which possesses a cluster of DnaA-binding sequences and a single binding site (IBS) for the DNA bending protein IHF (integration host factor). While IHF binding activates the datA function and is regulated to occur specifically at post-initiation time, the underlying regulatory mechanisms remain obscure. Here, we demonstrate that datA-IHF binding at pre-initiation time is down-regulated depending on the read-through transcription of datA IBS initiated at the glyV-X-Y promoter. During the cell cycle, the level of read-through transcription, but not promoter activity, fluctuated in a manner inversely related to datA-IHF binding. Transcription from the glyV-X-Y promoter was predominantly interrupted at datA IBS by IHF binding. The terminator/attenuator sequence of the glyV-X-Y operon, as well as DnaA binding within datA overall, contributed to attenuation of transcription upstream of datA IBS, preserving the timely fluctuation of read-through transcription. These findings provide a mechanistic insight of tRNA transcription-dependent datA-IHF regulation, in which an unidentified factor is additionally required for the timely datA-IHF dissociation, and support the significance of datA for controlling the cell cycle progression as a connecting hub of tRNA production and replication initiation.

Lack of expression of antigens for islet cell antibodies in rat fetal pancreas

It is not clear yet when pancreatic islet cells begin to express antigens for islet cell antibodies (ICA). Therefore, we studied whether human ICA-positive sera, crossreacting with adult rat islet cells, react with fetal and neonatal rat islet cells immunohistologically. The ICA did not react with fetal islet cells. On the other hand, neonatal islet cells over 2-3 weeks of age expressed the reactivities almost similar to those of the adult. It was suspected that pancreatic islet cells started to express their antigens to induce ICA gradually after birth.

Heterogeneity of human islet cell antibodies in terms of cross-species reactivity

There has been no consistent view about the cross-species reactivity of islet cell antibodies (ICA), and no report about their target antigens in the pancreatic islet cells of different species. Therefore, we examined the cross-reactivity of human ICA against rodent pancreatic islet cells, and found at least two types of ICA, one having a comparatively strong cross-reactivity and the other lacking it. Furthermore, using human as well as some rodent pancreatic tissues that had been modified chemically, we came to suspect that the target antigens of ICA were sialic acid residues of glycolipids. Therefore, we suggest that there are at least two types of ICA recognizing sialic acid residues of glycolipids, one reacting with antigen(s) commonly present in human and rat islets, and the other with antigen(s) only present in human islets.

[Differences in microvasculature between ethylnitrosourea-induced brain tumor and transplanted 9L cell brain tumor in the rat]

The microvasculature of ethylnitrosourea (ENU)-induced brain tumors and transplanted 9L cell brain tumors were studied in ultrathin sections and by the freeze fracture replica method. The vessels in ENU-induced tumors were similar to human glioma vessels in that they had endothelial tight junctions and increased pinocytotic vesicles. In the 9L cell tumors, the vessels lacked endothelial tight junctions and had fenestrated endothelium. Macroscopically, Evans blue dye penetrated the 9L cell tumors but not the ENU-induced tumors. Judging from the ultrastructure of the microvessels, the ENU-induced tumor appears more suitable as a human glioma model.

[Ultrastructural study of capillary permeability of liposome-encapsulated cisplatin in an experimental rat brain tumor model]

The anticancer chemotherapeutic agent cisplatin (cis-diamminedichloroplatinum) has several disadvantages, including extreme nephrotoxicity, rapid binding to plasma proteins, and poor penetration into the central nervous system. Liposomes would seem to be suitable as carriers of cisplatin to brain tumors. This ultrastructural study was undertaken to identify the capillary permeability of liposome-encapsulated cisplatin in a rat brain tumor model. Brain tumors were induced transplacentally with a single intravenous dose of 50 mg/kg of ethylnitrosourea (ENU). One ml of liposome-encapsulated cisplatin and ferritin prepared from phosphatidylcholine and cholesterol (molar ratio 7:2) was administered via the carotid artery to rats with ENU-induced brain tumors. The tumor platinum content and that of the contralateral hemisphere were assayed by flameless atomic absorption spectrometry. The presence of ferritin-bearing liposomes was demonstrated by electron microscopy of brain capillary endothelium as well as tumor cells. Thirty minutes after drug administration, the average dry-weight platinum concentrations were 3.98 +/- 0.50 micrograms/g within the intracerebral tumors and 0.72 +/- 0.24 micrograms/g in the contralateral hemispheres. Electron microscopic ultrastructural study, which can distinguish ferritin-bearing liposomes from cell materials, demonstrated the presence of liposomes containing ferritin in both cell surface folds and capillary endothelial cells and also within tumor cells. An enlarged electron micrograph of a liposome with a diameter of approximately 0.2 micron suggested the presence of ferritin molecules in the lamellar structure. Liposome-encapsulated cisplatin is apparently able to pass the blood-brain barrier and should be useful in the chemotherapy of glioma.

Brain edema in delayed radiation necrosis: study of capillary ultrastructure--case report

A 42-year-old male was found to have cerebral radiation necrosis 2 years after a split course of radiation therapy following subtotal excision of a left parasagittal meningioma. The surgical specimens were studied by means of conventional ultrathin sectioning and freeze-fracture replication techniques. The electron density of the capillary endothelium was decreased, as was the degree of surface infolding. The width was irregular, and there was an unusually large number of pinocytotic vesicles (37/micron 2). The endothelium was also discontinuous, and the basal laminae were irregular in thickness. The pericapillary space was markedly enlarged, and accumulation of a fibrin-like substance was noted in the extravascular space. The pericapillary zone contained inflammatory cells. However, the tight junctions were preserved and the intercellular junctions were composed of five strands that appeared to consist of continuous particles. The authors conclude that activated pinocytotic vesicles play an important role in increasing vessel permeability in delayed cerebral radiation necrosis and that leakage may occur through interruptions in the endothelium.

[Delayed cerebral radionecrosis associated with brain edema]

In a patient with a delayed cerebral radionecrosis, we examined the ultrastructural changes of capillaries and discussed the cause of the development of severe brain edema which is one of specific features of the radionecrosis. A 42-year-old male was found to have cerebral radionecrosis two and one-half years following split-course radiotherapy which was done after subtotal excision of a left parasagittal meningioma. The surgical specimens were studied with conventional ultrathin section and freeze-fracture replica techniques. The common characteristics of capillary endothelia were attenuation of its electron density, less degree of surface infolding, irregular thin and thick width, increased pinocytotic vesicles which were calculated as 37 per square micron with replica preparations. The discontinuity of endothelia was also revealed. The basal laminae were irregular in thickness. The pericapillary space was markedly enlarged. A fibrin-like substance accumulated in the extravascular space. Inflammatory cells also infiltrated the pericapillary zone. The tight junctions were preserved. The intercellular junctions were composed of 5 strands which appeared to be a continuous array of particles. We concluded that activated pinocytotic vesicles (vesicular transport) played an important role in increasing the permeability in the vessels of delayed cerebral radionecrosis, in addition to a possible leakage through discontinuity of endothelia.

[Brain edema after surgery of lateral ventricle tumors]

We reported five cases of lateral ventricle tumors all of which developed severe brain edema between 9 days and 8 years after surgery. Follow-up study with serial computed tomography before and after surgery were presented. Based on a review of the literature, a possible causal mechanism is suggested: 1) The cerebrospinal fluid diffuses into the white matter through the surgically damaged ependyma and caused severe postoperative edema; and 2) surgical blockade of the flow of cerebral interstitial fluid to drain into the fenestrated vessels of the choroid plexus and other periventricular areas caused severe postoperative edema.

A clinical study of long-term administration of dextran sulfate (MDS Kowa) in patients with retinopathy

We administered MDS at a daily dose of 1,800 mg to 25 patients with diabetic retinopathy for periods ranging from 12 to 48 months (mean: 28 months) and achieved the following results: 1) During the administration period total cholesterol, triglyceride and fibrinogen levels were all maintained at significantly lower levels. 2) Eye fundus findings showed an improvement in 38.9% no change in 47. 2% and a deterioration in 13.9% of the cases. 3) No side-effects or abnormalities in clinical findings were observed in any of the cases even though clinical tests of hepatic function, renal function, blood chemistry, and urinalysis were conducted. The above results demonstrate that MDS has a marked effect on diabetic retinopathy, especially in cases with moderate to severe symptoms during the non-proliferative stage.

Parinaud's syndrome in hydrocephalus due to a basilar artery aneurysm

A 65-year-old woman appeared with a progressive dementia, gait disturbance, and Parinaud's syndrome. A computed tomography scan, an angiogram of the vertebral artery, and metrizamide ventriculography demonstrated a marked hydrocephalus. A giant aneurysm at the termination of the basilar artery projected into the third ventricle producing partial obstruction of the aqueduct. The symptoms were resolved by a ventriculoperitoneal shunt; but after a month, the patient again showed the upward-gaze palsies concomitant with occurrence of shunt malfunction. The possible mechanisms of Parinaud's syndrome observed in the patient are discussed.

The manifestation of genotypes responsible for blood pressure and blood sugar level

It has been known for a long time that hypertension and diabetes mellitus are often complicated by each other. The aim of this paper was to disclose possible causes of such complications by investigating 1) whether or not hypertension and diabetes mellitus are entirely two independent diseases, 2) whether or not they occur together only by chance, 3) whether or not there are some causal factors which are shared by these two diseases and 4) whether or not these two diseases occur together with some probability. The genetic analyses of these two diseases were carried out on the basis of the genetic analyses on blood pressures (BP) and blood sugar levels (BS) in the present studies. It was proved that the genotypic correlation coefficients of BP and BS ranged from 0.075 to 0.573 with a mean value of 0.337 and their environmental correlation coefficients were from -0.029 to -0.337 with a mean value of -0.164. These results suggest that 1) the respective polygenic systems responsible for BP (hypertension) and BS (diabetes mellitus) have multiple effects and 2) the environmental factors responsible for BP and BS have inverse effects. The negative values of the environmental correlation coefficients between BP and BS indicate that the environmental factors which lower BP may elevate BS, and vice versa. An induction of an abnormal glucose tolerance as one of the side effects of thiazides, the most widely used anti-hypertensive diuretics, coincides with the inverse environmental correlation between BP and BS. This finding may be of great importance in the field of clinical genetics.