The pigmented epithelium sustains cell growth and tissue differentiation of chicken retinal explants in vitro

Embryonic retinae from 5-6-day-old chicks (E5-E6) were cut into stripes either in close contact with (RPE stripes) or in absence of the neighboring retinal pigmented epithelium (R stripes). The stripes were explanted and cultivated in vitro for up to 6 days, during which time they show the following differences in their characteristics of growth and differentiation. Compared with R stripes, RPE stripes morphologically showed a significant increase in size during the first 2 days in culture. Using E5 tissue, this is also demonstrated by a higher rate of cell proliferation (as measured by uptake of radioactive thymidine as well as by DNA contents). In contrast, R stripes after two days in culture show a much stronger neurite growth. After longer periods of culturing (5-6 days) we can show by cholinesterase histochemistry (AChE and BChE) and by PNA-lectin binding that the RPE stripes have started to form all major layers of the in vivo retina, whereas R stripes remain unstratified and start to degenerate earlier. We conclude that the pigment epithelium might exert a specific stimulus on growth and tissue differentiation of the neural retina not only during in vitro, but possibly also during in vivo development. The in vitro methods introduced here could become useful model systems to further investigate the significance of the RPE for developmental, regenerative and even adult processes of the neural retina. Their future applicability in ophthalmologic research is briefly discussed.

Regulation of vasopressin and oxytocin synthesis in anterior pituitary and peripheral tissues

Recent studies have demonstrated the presence of immunoreactive oxytocin (OT) and vasopressin (VP), OT and VP receptors and physiological functions for these two hormones in a variety of peripheral tissues, including anterior pituitary gland. The objectives of this study were to determine if (i) OT and VP genes are expressed in rat testis and anterior pituitary gland and (ii) if osmotic stimulation known to modify the regulation of OT and VP genes in hypothalamus, would modify the expression of these genes in rat testis and anterior pituitary gland. Using oligonucleotide probes (courtesy of Drs. M. Brownstein and W. Scott Young, NIMH) corresponding to the VP gene or OT gene and specific fractions of human OT and VP genes (courtesy of Dr. J. Battey, NCI) subcloned in the pGEM-3 riboprobe system, and Northern blot and slot blot techniques, OT and VP mRNAs were found in rat testis and anterior pituitary gland. When adult male rats (SD) were either deprived of drinking water or offered 2% salt solution as a sole source of drinking fluid for 72 hrs, both OT and VP mRNA levels were increased in hypothalamus, anterior pituitary gland and testis. Our data suggest that testis and anterior pituitary gland could also be sites of synthesis of OT and VP and that the same stimulus may regulate these genes in various tissues.

Comparison of pulsatile subcutaneous gonadotropin-releasing hormone and exogenous gonadotropins in the treatment of men with isolated hypogonadotropic hypogonadism

Eight men with isolated hypogonadotropic hypogonadism were treated with pulsatile gonadotropin-releasing hormone (GnRH) after maximal testicular growth and function had already been achieved with human chorionic gonadotropin (hCG) and human menopausal gonadotropin (hMG). Only four subjects could normalize plasma testosterone (T) levels (group A). After 18 months of GnRH therapy, testicular size of group A increased by 53% (P less than 0.01) over that previously attained with exogenous gonadotropins. However, despite further testicular growth, two men who were previously azoospermic on hCG/hMG remained so on GnRH. In the other two patients, total sperm count increased minimally. Thus, pulsatile gonadotropin levels achieved with GnRH are more effective in stimulating testicular growth, but not necessarily sperm output, than are stable gonadotropin concentrations obtained with hCG/hMG.

Rapid identification of bacterial genes that are lethal when cloned on multicopy plasmids

A procedure to identify genes that are lethal when cloned on multicopy plasmids was developed. It depends on the ability of mini-Mu plasmid elements to be used for both in vivo cloning and generalized transduction of enterobacterial genes. The feasibility of this procedure was demonstrated by using the tetA gene of Tn10, which is lethal when in multiple copies in the presence of 25 micrograms of tetracycline per ml.

[Postoperative radiation of retinoblastoma--report on 22 patients]

From July 1958 to December 1979, 22 patients with retinoblastoma were treated postoperatively by radiotherapy. All were proved by pathology. There were 12 stage I, 1 stage II, 8 stage III and 1 stage IV lesions. Radiation dose was more than 15 Gy and most of the patients received 40-50 Gy in 4-5 weeks. The overall cancer free 5 year survival rate was 55% (12/22). The 5 year survival rate of stage I patients was 75% (9/12), and that of stage III patients was 38% (3/8). None of the stage II and IV patients survived. Dose of 40-50 Gy/4-5 wk is considered to be optimal for control of the tumor. Dose higher than 60 Gy/6 wk could lead to retarded growth in the orbital and temporal bony structures if the patient survives for ten years or more.

Serum testosterone response to desialylated human choriogonadotropin in man

To assess the in vivo steroidogenic activity of desialylated human choriogonadotropin (hCG) in man, highly purified desialylated hCG was administered as a constant intravenous infusion over 6 hours to four normal men at a rate sufficient to maintain substantial levels of desialylated hCG in the serum. The mean percent change of serum testosterone from baseline during the first 6 hours in men given an infusion of desialylated hCG was compared to that in saline-infused controls and that in men given highly purified intact hCG. The mean change of serum testosterone at 6 hours in the group infused with desialylated hCG (129% of baseline) was significantly greater than that of the controls (69% of baseline). Furthermore, the response to desialylated hCG could not be distinguished from that of hCG (125% of baseline). It was concluded that desialylated hCG, when given as a constant intravenous infusion, can elicit a substantial serum testosterone response comparable to that seen with purified hCG, and thus, that desialylated hCG behaves as an agonist of the LH/CG receptors on human Leydig cells.

Rapid sequencing of cloned DNA using a transposon for bidirectional priming: sequence of the Escherichia coli K-12 avtA gene

A new approach to determining the sequence of cloned DNA is described. Unique regions near each end of the transposable element gamma-delta provide a pair of "portable" primer-specific sites for bidirectional sequencing by the dideoxy chain termination method. A set of gamma-delta insertions positioned about 200 bp apart over the entire cloned DNA allowed us to determine the sequence of both strands in a single parental plasmid without subcloning. The avtA (alanine-valine transaminase) gene of E. coli K-12 was sequenced by this approach. Surprisingly, gamma-delta insertions downstream of the coding region were found to significantly reduce avtA expression. We suggest that these nondisruptive insertions probably change the DNA topology and thereby alter gene expression.

Cloning and characterization of the Escherichia coli K-12 alanine-valine transaminase (avtA) gene

avtA, which encodes the alanine-valine transaminase, transaminase C, was cloned in vivo with high- and low-copy-number mini-Mu cloning vectors. The phenotype conferred by the cloned avtA+ gene usually depended upon the plasmid copy number; most high-copy-number avtA+ plasmids permitted isoleucine-requiring ilvE strains to grow in the absence of isoleucine (multicopy suppression), while low-copy-number avtA+ plasmids did not. avtA was mapped to a 1.25-kilobase segment by comparison of the restriction maps of 24 independent mini-Mu plasmids and then by gamma-delta (Tn1000) mutagenesis of a pBR322-avtA+ plasmid. The direction of transcription of avtA on the cloned fragment was determined with fusions to a promoterless lac gene.

High frequency generalized transduction by miniMu plasmid phage

Deletion derivatives of phage Mu which replicate as multicopy plasmids, and also transpose and package like Mu, have been developed for the in vivo cloning of bacterial genes. We show here that these miniMu plasmid phage are also efficient at generalized transduction and that both in vivo cloning and generalized transduction of a given gene can be accomplished in a single experiment.

Mouse histone H2A and H2B genes: four functional genes and a pseudogene undergoing gene conversion with a closely linked functional gene

The sequence of five mouse histone genes, two H2a and three H2b genes on chromosome 13 has been determined. The three H2b genes all code for different proteins, each differing in two amino acids from the others. The H2b specific elements present 5' to H2b genes from other species are present in all three mouse H2b genes. All three H2b genes are expressed in the same relative amounts in three different mouse cell lines and fetal mice. The H2b gene with the H2b specific sequence closest to the TATAA sequence is expressed in the highest amount. One of the H2a genes lacks the first 9 amino acids, the promoter region, the last 3 amino acids and contains an altered 3' end sequence. Despite these multiple defects, there is only one nucleotide change between the two H2a genes from codon 9 to 126. This indicates that a recent gene conversion has occurred between these two genes. The similarity of the nucleotide sequences in the coding regions of mouse histone genes is probably due to gene conversion events targeted precisely at the coding region.

Chronic sex steroid exposure increases mean plasma growth hormone concentration and pulse amplitude in men with isolated hypogonadotropic hypogonadism

Sex steroid administration can increase the GH response to provocative stimuli, but the relationship of sex steroids to spontaneous GH secretion is still controversial. We sought to characterize the effect of sex steroids on the plasma GH concentration by examining the 24-h pattern of episodic GH secretion in nine previously untreated adult men with isolated hypogonadotropic hypogonadism before and during long term testosterone, gonadotropin, or pulsatile GnRH treatment. After chronic sex steroid exposure, the mean 24-h plasma GH level, mean GH pulse amplitude, and mean area under the curve of pulses were significantly increased compared to pretreatment values [3.2 +/- 1.8 ( +/- SD) vs. 1.8 +/- 1.2 ng/mL (P less than 0.01); 11.4 +/- 7.2 vs. 5.5 +/- 4.4 ng/mL (P less than 0.05); and 720 +/- 547 vs. 316 +/- 371 ng/mL X 20 min (P less than 0.05), respectively], while mean 24-h pre- and posttreatment GH pulse frequencies were indistinguishable (5.7 +/- 2.1 posttreatment vs. 5.0 +/- 3.2 pretreatment; P = NS). The mean posttreatment plasma somatomedin-C level also rose significantly during treatment (1.89 +/- 0.65 vs. 1.28 +/- 0.48 U/mL; P less than 0.01). We conclude that the increase in the mean plasma GH level during chronic sex steroid exposure is due mainly to augmentation of GH pulse amplitude, and that sex steroids probably increase spontaneous GH secretion.

Equilibrium and local stability in a logistic matrix model for age-structured populations

A logistic matrix model for age-structured population dynamics is constructed. This model discretizes a continuous, density-dependent model with age structure, i.e. it is an extension of the logistic model to the case of age-dependence. We prove the existence and uniqueness of its equilibrium and give a necessary and sufficient condition for the local stability of the equilibrium.

Liquid and solid two-phase radioimmunoassay--simultaneous measurement of levels of triiodothyronine and thyroxine of human serum in a single specimen

The principle of the liquid and solid two-phase radioimmunoassay and its application to measuring the concentrations of triiodothyronine and thyroxine of human serum in a single sample at the same time are described in this paper. Rabbit anti-triiodothyronine antiserum was immobilized on the inner surface of a plastic tube as solid-phase radioimmunoassay system of testing triiodothyronine and donkey anti-rabbit gamma globulin antiserum was used to separate immunocomplex in liquid-phase radioimmunoassay system of thyroxine reaction. In both systems, radioiodine-125-labelled antigens were used as tracer. Through simple calculation, we can get the results of serum concentrations of triiodothyronine and thyroxine in a single sample. Compared with classical single-component radioimmunoassay of triiodothyronine and thyroxine and by methodological appraisal of two-phase radioimmunoassay itself, this method has the advantages of very high efficiency, reliability and also has the same specificity and precision.

Growth and differentiation of transplanted rat embryos in intact, diabetic and hypophysectomized hosts: comparison with their growth in situ

The objectives of this investigation were to evaluate the suitability of a transplant system for studying the endocrine control of growth and differentiation in rat embryonic/fetal tissues, and to gain information on the development of their hormone dependence. Whole 10-day-old rat embryos were transplanted under the kidney capsule of intact, hypophysectomized (Hx) or diabetic (Db) juvenile syngeneic female hosts, and grown there for 3, 6, 9 or 12 days. The wet weight, DNA and protein content of the transplants and of age-matched in situ embryos/fetuses were measured to assess their growth. The transplants in intact hosts increased more than 300-fold in all parameters during 12 days of incubation. However, this increase was only about 4% of the in situ growth. The severe impairment in growth occurred mainly during the first 3-day period when the transplants grew only 5% as much as the in situ embryos. Between days 13 and 22 of gestational age, the increment in transplant growth was 70% of that occurring in situ. Tissue differentiation of the transplants in intact hosts was essentially normal, although they grew as teratomas. Growth and differentiation of transplants in Db and Hx hosts were delayed or inhibited. This inhibition occurred as early as day 3 after transplantation and was corrected by appropriate hormone replacement therapy of the hosts. We conclude that rat embryos/fetuses develop a dependence on a growth hormone-dependent factor (possibly somatomedin) and/or insulin for growth before day 13 of development. This transplant system will be useful for studying other aspects of the control of growth and differentiation of rat embryos/fetuses between days 10 and 22 of gestation.

In-vivo studies of amphotericin B liposomes derived from proliposomes: effect of formulation on toxicity and tissue disposition of the drug in mice

The repeat dose toxicity of various liposomal formulations containing amphotericin B has been determined in mice. In general, small liposomes (e.g. 100-150 nm) were found to be more toxic than their large counterparts (e.g. about 2000 nm). However, the repeat dose toxicity of small liposomes could be diminished substantially by the inclusion of sterol (i.e. ergosterol) into the liposomal membranes. Tissue accumulation studies of amphotericin B after repeat dosing may be a useful adjunct to formulation development.

Characterization of myogenic cell lines derived by 5-azacytidine treatment

Three myogenic clonal cell lines were isolated from C3H 10T1/2 C18 cells (10T1/2) treated with 5-azacytidine (5-aza-CR). These lines reproducibly underwent fusion at confluence into functional myotubes capable of contracting in response to acetylcholine. The degree of fusion could be increased two- to threefold if the cells were grown on gelatin-coated dishes. All of the cell lines lost some of their myogenic potential after repeated passaging and the percentage of colonies capable of forming muscle was not increased by permissive media containing 2% horse serum. The 10T1/2 cells expressed only the BB form of creatine phosphokinase but all of the myogenic clones expressed additionally the MM and MB forms of the isozyme after fusion. The overall genomic level of 5-methylcytosine was decreased in some but not all of the cell clones tested. Comparisons between the 10T1/2 cells which never form muscle without 5-aza-CR treatment and clonal derivatives of committed cell types might be of value in understanding the molecular basis of the commitment process.

Inhibition of cell proliferation by cytosine-arabinoside and its interference with spatial and temporal differentiation patterns in the chick retina

Incubation of chick embryos with 200 nmoles/egg of cytosine arabinoside (AraC) completely inhibits cell proliferation in the embryo. At an age older than embryonic day 4 (E4) more than 90% of the embryos survive this treatment. The drug induces various malformations; in particular the retina is heavily affected. This simple method offers the possibility to study the effect of a more or less decreased cell production on processes of further differentiation and histogenesis of retinal tissue. The following results are obtained: In spite of the inhibition of cell proliferation in the retina by AraC an abnormally thick basal lamina is found and the expansion of the eye still proceeds, indicating that eye growth is not only dependent on retinal cell numbers. Stereotyped malformations of retinal histogenesis are induced and categorized into three groups: in addition to areas of normal structure cells are found arranged in rosettes and in half-rosettes sometimes linked by areas of undefined transient cell arrangements. The results point to a strong tendency of a severely diminished cell population to form regularly laminated retinal-like structures as long as a minimal ratio of cell types is given. The spatio-temporal appearance of the type of retinal malformation in a given retinal area is dependent on the time of AraC exposure and thus on the degree of differentiation reached at a "spatio-temporal spot": Full rosettes develop at earlier, and half-rosettes at later stages of AraC interference. Furthermore, deformities first appear on temporal and ventral sides. Thus, the establishment of these malformations follows and reflects the normal sequence of differentiation within the retina. Cells within rosettes organize in specific layers and start to differentiate normally. This shows that earlier formed cells are not dependent on the influence of factors derived from cells that are formed later for their proper differentiation.

Variable effects of DNA-synthesis inhibitors upon DNA methylation in mammalian cells

Post-synthetic enzymatic hypermethylation of DNA was induced in hamster fibrosarcoma cells by the DNA synthesis inhibitors cytosine arabinoside, hydroxyurea and aphidicolin. This effect required direct inhibition of DNA polymerase alpha or reduction in deoxynucleotide pools and was not specific to a single cell type. At equivalently reduced levels of DNA synthesis, neither cycloheximide, actinomycin D nor serum deprivation affected DNA methylation in this way. The topoisomerase inhibitors nalidixic acid and novobiocin caused significant hypomethylation indicating that increased 5-mCyt content was not a necessary consequence of DNA synthesis inhibition. The induced hypermethylation occurred predominantly in that fraction of the DNA synthesized in the presence of inhibitor; was stable in the absence of drug; was most prominent in low molecular weight DNA representing sites of initiated but incomplete DNA synthesis; and occurred primarily within CpG dinucleotides, although other dinucleotides were overmethylated as well. Drug-induced CpG hypermethylation may be capable of silencing genes, an effect which may be relevant to the aberrantly expressed genes characteristic of neoplastic cells.

Interferon inhibits the growth of Legionella micdadei in mouse L cells

The intracellular growth of Legionella micdadei was inhibited in mouse L cells treated with interferon (IFN). This IFN-mediated restriction was dose-dependent and required preincubation of the L cells with high doses of IFN (1,000 U/ml) for maximal inhibition. Incubation of L. micdadei with IFN alone had no detectable effect on growth of the bacteria. The IFN-mediated growth restriction was not dependent upon tryptophan concentration in the culture medium.

Evidence that synthetic 31-amino acid inhibin-like peptide lacks inhibin activity

We studied the biological activity of a recently characterized 31-amino acid inhibin-like peptide (ILP) using a synthetic preparation. While the material yielded a single component on chromatography, amino acid sequence analysis suggested that only 30% of the molecules possess the complete structure. Bioactivity was tested in vitro using whole pituitaries from 25 day-old male Sprague-Dawley rats. Pituitaries were incubated with 500 ng/ml of the ILP preparation or vehicle alone for 60 min, followed by a 3 h exposure to 2 ng/ml of luteinizing hormone releasing hormone (LHRH) or its diluent. In the ILP-incubated pituitary media, no significant suppression of basal FSH and LH release or stimulated FSH release was observed, while a significant increase in stimulated LH release was seen (p less than 0.05). An in vivo bioassay study was performed on 38 day-old male Sprague-Dawley rats. Test animals were injected with 0.1, 1, 10 or 20 mcg of ILP immediately after castration, and 10 and 24 h later. Control animals received bovine serum albumin or vehicle alone. There were no statistically significant differences in serum LH or FSH concentrations taken at 30 h after castration between the ILP-treated rats and controls. Possible reasons for our inability to demonstrate inhibin bioactivity (selective FSH suppression) with this ILP preparation include: Only about 30% of the peptides had the complete amino acid sequence. Other peptides with deletions might have acted as antagonists, thus obscuring the inhibin bioactivity. The 31-amino acid ILP may not be the authentic inhibin molecule. We suggest that further studies are needed to determine the true identity of inhibin.

Role of topoisomerase II in mediating epipodophyllotoxin-induced DNA cleavage

Epipodophyllotoxins are an important new class of anticancer agents which include the compounds VM-26 (teniposide) and VP-16 (etoposide). The mechanism of action of these drugs appears to involve production of DNA single- and double-strand breaks by virtue of a temperature-sensitive interaction between drug and a heat-labile intranuclear component. We now report evidence indicating that type II topoisomerase is the likely intracellular target for the DNA strand-breaking effects of the epipodophyllotoxins. Both VM-26 and VP-16 stimulate site-specific DNA cleavage by a highly purified calf thymus type II topoisomerase. VM-26 is 5- to 10-fold more potent than VP-16 in this assay, a difference that is also seen when DNA strand breaks are assayed in isolated nuclei of mouse leukemia cells following drug exposure. Furthermore, a similar potency difference exists with respect to cytotoxicity. Equilibrium dialysis experiments using [3H]VP-16 indicate that the drug does not bind to DNA. Thus, we suggest that the epipodophyllotoxins exert their anti-cancer effects by "poisoning" type II topoisomerase without binding to DNA. In this regard, their actions may be analogous to those of nalidixic acid in bacteria.

Dissection of serological and cytolytic T lymphocyte epitopes on murine major histocompatibility antigens by a recombinant H-2 gene separating the first two external domains

A novel H-2 gene in which the first external (N) domain of the H-2Ld antigen was replaced with that of the H-2Dd antigen was constructed and introduced into L cells. A transformant expressing the products of the hybrid gene was studied for binding to monoclonal antibodies specific for H-2Ld and H-2Dd antigens. It was found that serological determinants are distributed both in the N (Dd) and Cl (Ld) domains. Determinants recognized by allospecific cytotoxic T lymphocytes (CTLs) and virus-specific CTLs also mapped to the N and Cl domains. Determinants recognized by vesicular stomatitis virus (VSV)-specific effect cells, however, were not present on the recombinant molecule. These results show that a recombinant gene of two H-2 antigens in which the first external domain has been reshuffled can express a functional H-2 antigen that can then be used to map serological and CTL determinants to specific domains.

Spatio-temporal patterns of differentiation of whole heads of the embryonic chick as revealed by binding of a FITC-coupled peanut-agglutinin (FITC-PNA)

The spatio-temporal expression of specific binding sites for FITC-labeled peanut agglutinin (Arachis hypogaea) in frozen sections of whole embryonic heads of the chick between embryonic day 2 (E2) and embryonic day 8 (E8) is described. PNA-binding sites are present already at E2 on the external limiting membrane and the ventricular boundary of the neural wall. With progressing differentiation fluorescent bands are formed from the outside of the neural wall radiating inside, forming second layers inside the CNS at later stages. The visual system (retina and tectum) shows remarkably little PNA-binding activity until about E7/8, a time when binding sites in the other brain areas are already most abundant. In the telencephalon a fuzzy distribution of fluorescence is found. A possible significance of this finding for fiber guidance from the retina to the tectum is briefly discussed. Local high activities can be observed in different parts of the brain. Intense bands of PNA-fluorescence on parts of the epidermis, along the eye cups, around the fore- and hindbrain and in the medial part of the mesenchyme delineate early biochemical compartments foreshadowing the succeeding ossification.

Recurrent thyrotoxicosis after I-131 induced hypothyroidism

The first clinically and biochemically documented case of recurrent thyrotoxicosis after I-131 induced hypothyroidism in a patient with Graves' disease is reported. Two months after the administration of 9.2 mCi of I-131, the subject developed hypothyroidism. One month later, the patient became euthyroid. Then, nine months following ablation, the patient again developed thyrotoxicosis. A second dose of I-131 of 12.5 mCi was required to finally produce permanent hypothyroidism. This case illustrates the recurrence of hypothyroidism after what had seemed to have been adequate I-131 radiation.

Binding of FITC-coupled peanut-agglutinin (FITC-PNA) to embryonic chicken retinas reveals developmental spatio-temporal patterns

FITC-labeled peanut agglutinin (PNA), a lectin from peanut (Arachis hypogaea) which binds specifically to D-galactose, was used as a probe to trace the distribution of PNA-lectin receptors during early development of chick retina. We found that specific fluorescence within the inner plexiform layer (IPL) and the outer plexiform layer (OPL) appears at different developmental stages. The specific fluorescence of the IPL first appears near the central area of the ventro-posterior quadrant of the 7-day retina, then extends progressively towards the periphery, reaching the ora serrata earlier on the posterior than on the anterior side. The development of the specific fluorescence of the OPL follows the same scheme, but it appears later (starting at day 9) than that of the IPL and it is less pronounced. The spatio-temporal patterns of the expression of the lectin receptors show relationships to those of withdrawal of proliferating cells from mitosis, and of other events related to differentiation.