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J Bernal

Publications and source records attributed to J Bernal.

At least 109 records · Page 6Linked to original sources
PubMed1990

Patterns of cerebral cortex mRNA expression.

A pool of 163 clones, isolated by screening 60,000 members of a Macaca fascicularis cerebral cortex cDNA library with a cortex-minus-cerebellum subtracted probe prepared by the phenol enhancement method, was analyzed by Northern blot hybridization studies. One hundred fifty-three of these clones corresponded to 22 RNAs whose abundance was at least 2-fold higher in cerebral cortex poly(A)+ RNA samples than in samples of cerebellar poly(A)+ RNA. Seven of these RNAs, represented by 131 clones, were undetectable in cerebellum. Only 10 of the 163 clones proved to be false positives. The abundance of several of these cortex-enriched RNAs was altered in Alzheimer's disease brains. Several RNAs that were present in cerebral cortex but undetectable in cerebellum were generally enriched in telencephalon, although none was restricted to the cortex. One of the cortex enriched RNAs, whose nucleotide sequence is presented, encoded monkey preprocholecystokinin. Overall, this study provides insights into the powers and limitations of subtractive hybridization and into the patterns of gene expression in the central nervous system.

Alzheimer Disease↗
PubMed1990

T3 receptor occupancy and T3 levels in plasma and cytosol during rat brain development.

The concentration and occupancy of the thyroid hormone receptor have been measured in rat brain nuclear extracts at the end of the fetal period and during the postnatal period. Receptor occupancy attained maximal values at postnatal day 15 (52% of total receptor binding sites occupied by T3) and correlated with plasma and cytosol total and free T3. The values for these parameters showed greater differences throughout development than did receptor occupancy. From gestational day 21 to postnatal day 15, total T3 increased in plasma from 0.18 to 1 nmol/l and in cytosol from 1 to 7.5 pmol/l. Free T3 increased in plasma from 1.2 to 6 pmol/l and in cytosol from 8 to 59 pmol/l. Nuclear free T3, calculated on the basis of receptor occupancy, and Kd increased in parallel, from 39.8 to 107 pmol/l at the same ages. Values for nuclear free T3 were between 2 and 5 times those in cytosol and between 10 and 40 times those in plasma, suggesting the presence of a small free T3 gradient from plasma to the nucleus. All of the above changes take place during the critical period of oligodendrocyte differentiation and the start of myelin gene expression, suggesting that thyroid hormone influences these important events of brain maturation.

Aging↗
PubMed1989

Generalized deficiency of 3,5,3'-triiodo-L-thyronine (T3) in tissues from rats on a low iodine intake, despite normal circulating T3 levels.

Rats fed a low iodine diet have decreased total and nuclear T3 concentrations in the liver and brain, as compared with rats supplemented with iodine, possibly because of the very low plasma and tissue T4 pools in low-iodine diet rats, leading to decreased intracellular generation of T3 in those tissues. If so, T3 levels should not decrease in heart and skeletal muscle, as plasma T3 is normal in low-iodine diet rats and these two tissues derive their intracellular T3 directly from plasma T3. We have studied this point in male rats fed a low-iodine diet, a low-iodine diet + iodine, and the stock diet. As in previous studies, low-iodine rats had very low plasma T4 and high plasma TSH levels, plasma T3 levels being normal. Liver T3 decreased, and so did the brain T3 levels despite a compensatory increase in type II 5' iodothyronine deiodinase activity. Contrary to expectations, T3 concentrations were lower in the heart and skeletal muscle of low-iodine diet rats. Attempts to clarify the possible mechanism(s) involved have been unsuccessful so far. The present results show that, despite normal plasma T3, a deficiency of T3 occurs in more tissues of rats on a low iodine intake than previously assumed. If the present results are pertinent to inhabitants from areas with severe iodine deficiency, it would appear that they might suffer from a generalized tissue T3 deficiency (and hypothyroidism?), even if overt clinical signs are not usually present.

Animals↗
PubMed1988

Preferential saturation of brain 3,5,3'-triiodothyronine receptor during development in fetal lambs.

The concentrations of T4 and T3 were measured in brain, liver, and lung of fetal lambs at 100 days gestational age. The highest concentrations of T4 were found in lung (26.8 ng/g). Brain T4 (8.8 ng/g) was only 30% of lung T4. In contrast, higher concentrations of T3 were found in brain (1.8 ng/g) than in lung (0.39 ng/g) or liver (0.36 ng/g). Nuclear T3 was 16% of the total T3 in brain and 44% of that in lung. The degree of saturation of the nuclear T3 receptor was estimated from the concentrations of nuclear T3 and nuclear receptor. Receptor saturation was low in liver and lung (10%) and high in brain (74%). Receptor occupancy was also measured directly in vitro by comparing the binding of [125I]T3 in nuclear extracts at 0 and 20 C. This method is based on the different rates of dissociation of the T3-receptor complex at these temperatures (0.045 and 0.618 h-1, respectively). Therefore, [125I]T3 was bound mainly to unoccupied sites at 0 C, whereas at 20 C it bound to unoccupied sites plus a fraction (70%) of endogenously occupied sites. There was no difference in binding at the two temperatures using lung extract, reflecting a very low occupancy. Data from brain suggested 61% receptor saturation. Total and free T3 were measured in plasma and in lung and brain cytosols, and the figures were compared to the intranuclear free T3 calculated by the law of mass action, from the affinity and saturation of receptor. In lung, the concentrations of cytosolic (5.4 +/- 1.9 pM) and nuclear (8.6 pM) free T3 were similar to that of plasma T3 (3.7 +/- 0.99 pM). In contrast, brain cytosolic (14.9 +/- 1.2 pM) and nuclear (203 pM) free T3 revealed the presence of free T3 gradients from cytosol to plasma (4-fold) and from nucleus to cytosol (13.6-fold). The data suggest that the sheep brain is a major target of thyroid hormone action at the end of the neuroblast proliferation period. Mechanisms are locally present in the brain at this stage of development to ensure a high saturation of the nuclear T3 receptor.

Animals↗
PubMed1988

Estimation of nuclear thyroid hormone receptor saturation in human fetal brain and lung during early gestation.

The total number and saturation of nuclear receptors for T3 were measured in human fetal brain and lung from the 9th to the 13th week of fetal life. The concentrations of occupied and unoccupied receptor sites were determined by measuring total binding capacity at 0 and 22 C. At 0 C [125I]T3 was bound mainly to unoccupied sites, whereas at 22 C it was bound to unoccupied sites plus a fraction (70%) of endogenously occupied sites. Saturations of brain and lung receptors were similar (12-27%). From the fractional receptor occupancy and the receptor dissociation constants (34 pmol/L in brain and 56 pmol/L in lung) the concentration of intranuclear free T3 was calculated to be 9 pmol/L in brain and 11 pmol/L in lung. Total and free cytosolic T3 were measured by RIA and equilibrium dialysis. Total T3 was below the limit of detection in lung (90 pmol/L). The concentration of free T3 in brain cytosol was 0.95 pmol/L at 11 weeks and 2.96 pmol/L at 13 weeks, i.e. considerably lower than the nuclear free T3 concentration. These results suggest the presence of a small gradient (3-fold) between nuclear and cytosolic free T3 in both fetal tissues. The data strongly support the idea that thyroid hormones influence human brain development at least from the 9th to the 10th week of gestational age.

Brain↗
PubMed1987

Inhibition of nuclear binding of triiodothyronine by antimycin A in cultured human fibroblasts.

We have tested the effects of several cell inhibitors on cell and nuclear content of T3 at equilibrium in cultured human fibroblasts. Monodansylcadaverine and colchicine inhibited in parallel, and near to the same extent, cell and nuclear content of T3. Antimycin A did not interfere with cell accumulation of T3 but induced a 10-fold decrease of nuclear T3. This effect was due to a decrease of the apparent affinity constant of the T3 nuclear receptor. Other metabolic inhibitors such as sodium azide or potassium cyanide were without effects. It is suggested that antimycin A blocks a nuclear T3 concentrating mechanism which maintains a gradient of free T3 between the nucleus on the one hand, and the cytosol and plasma, on the other.

Antimycin A↗
PubMed1987

Ontogenesis of thyroid hormone receptor in foetal lambs.

Affinity and concentration of T3 receptor sites have been measured in nuclear extracts from the brain, lung, and liver of foetal lamb tissues at 50, 82 and 100 days of gestational age. Control experiments indicated that the concentration of sites was similar when nuclear extracts or purified nuclei were used, and that maximal binding capacity was obtained after 2 h of incubation at 22 degrees C. The pattern of receptor binding affinity when different thyroid hormone analogs were used in competition assays with [125I]T3 was T3 greater than 3,5,3'-triiodothyroacetic acid (Triac) greater than T4 in the lung and brain. In the liver, Triac had the same affinity as T3. The sedimentation coefficient of the receptor was 3.6 S in lung. There were minor changes of receptor affinity in the brain, but not in the lung or liver, during development with the highest value at 82 days. Receptor concentration increased twice from 50 to 82 days. Since in the brain this is the period of neuroblast proliferation, the results suggest that thyroid hormone is required for proper foetal lamb development and, in particular, for neuroblast proliferation and/or differentiation.

Animals↗
PubMed1985

The early ontogenesis of thyroid hormone receptor in the rat fetus.

We have determined the concentration of thyroid hormone receptor binding sites in nuclear extracts derived from rat fetal organs throughout gestation and the postnatal period. Before day 14 of gestation nuclear extracts were obtained from whole fetuses. No receptor binding activity could be detected at day 12 of gestational age, and small amounts were detected at day 13 (maximum binding capacity less than 50 fmol/mg DNA). The receptor could be measured in pools of individual organs from day 14 (brain) or from day 16 (heart, liver, and lung) onwards. The order of analog binding affinity at 14 days was triiodothyroacetic acid = T3 greater than T4 greater than rT3, suggesting that at 14 days of fetal age the receptor has the same binding specificity as the receptor from mature tissues. In brain, the concentration of binding sites increased from 77 fmol/mg DNA at 14 days to 210 fmol/mg DNA at 17 days, remaining at this level until birth. Receptor concentration was identical whether the binding assays were performed on purified nuclei or nuclear extracts. There was no effect of maternofetal hypothyroidism on receptor concentration in the brain at 21 days of gestational age. Lung concentrations of receptor also remained constant during the fetal period. During the postnatal period, there was an increase in receptor concentration in brain and lung, with maximum levels at day 6. The pattern of receptor development in heart and liver was different, since its concentration increased progressively throughout the fetal and postnatal periods towards the levels found in adult rat tissues. The results suggest that the appearance of the thyroid hormone receptor coincides with that of the first fetal thyroid gland structures, but that it occurs much before thyroid function is fully established. As far as the receptor is concerned, fetal tissues have the potential to respond to thyroid hormone as early as the 13th day of gestational age.

Animals↗
PubMed1985

Dissociation of the triiodothyronine receptor from the nucleus induced by cations: evidence for divalent cation sensitive and insensitive nuclear sites.

Aliquots of purified rat liver nuclei were diluted at 0 degrees C in isotonic buffers containing monovalent (Na+) or divalent (Ca2, Mg2+) cations. At different times following dilution the nuclear suspensions were centrifuged and the T3 receptor was measured in KCl extracts of the nuclear pellets. The rate of receptor loss after dilution in EDTA was 0.0025 min-1. Dilution in the presence of cations caused a fast release of receptor during the first 10 min. This phase, which was not observed when the nuclei were diluted in EDTA without salt, was followed by a second phase where the receptor was released at the same rate as in EDTA. Receptor release was only dependent on the presence of cations in the dilution buffer during the first 10 min after dilution. The amounts of receptor remaining in the nuclei after the first 10 min of dilution were 51.8 +/- 9.2%, in the presence of Ca2+ and Mg2+, 38.6 +/- 8.9% in 0.15 M NaCl, and 18.0 +/- 4.8% in 0.15 M NaCl in the presence of Ca2+ and Mg2+. The release of receptor was not influenced by the integrity of the nuclear membrane. These results suggest the presence of divalent cation sensitive and insensitive nuclear sites for the T3 receptor, in amounts which could be estimated to be about 48 and 52%, respectively. Other interpretations are also possible, such as the presence of a high proportion of free receptors in the nucleosol, which could be released during the first phase of dilution if the negative charges in chromatin are blocked by cations to avoid redistribution of receptors immediately after dilution.

Animals↗
PubMed1984

Ontogenesis of the nuclear 3,5,3'-triiodothyronine receptor in the human fetal brain.

A high-affinity T3 binding site with the binding specificity of the nuclear T3 receptor is present in the brain of the human fetus at midgestation. Its concentration was found to be very low at 10 weeks of gestation, and increased by a factor of 10 up to the 16th week, in coincidence with the period of neuroblast multiplication. Liver, heart, and lung also contained receptor. Both T4 and T3 were present in the brain, as measured by RIA. In other tissues, however, only T4 was detected, suggesting that brain T3 in the fetus arises from local 5'-deiodination of T4. The results suggest that the human fetal brain is a potential target of thyroid hormone at midgestation.

Brain↗