A symmetric, triply interlaced 3-D anionic MOF that exhibits both magnetic order and SMM behaviour.

A newly prepared 3-D polymer of cobalt citrate cubanes bridged by high-spin Co(ii) centres displays both single-molecule magnet (SMM) behaviour and magnetic ordering. Triple interpenetration of the 3-D diamondoid polymers yields a crystalline solid with channels that host cations and free water molecules, with the SMM behaviour of the Co4O4 cores preserved. The octahedrally coordinated Co(ii) bridges are implicated in the onset of magnetic order at an experimentally accessible temperature.

Persistence of slow dynamics in Tb(OETAP)2 single molecule magnets embedded in conducting polymers.

UNLABELLED: The spin dynamics of Tb(OETAP)2 single ion magnets was investigated by means of muon spin relaxation (µSR) both in the bulk material as well as when the molecule is embedded into PEDOT: PSS polymer conductor. The spin fluctuation time is characterized by a high temperature activated trend, with an energy barrier around 320 K, and by a low temperature tunneling regime. When the single ion magnet is embedded into the polymer the energy barrier only slightly decreases and the fluctuation time remains of the same order of magnitude, even at low temperature. This finding shows that these single molecule magnets preserve their characteristics which, if combined with those of the conducting polymer, result in a hybrid material of potential interest for organic spintronics.

COUP-TF upregulates NGFI-A gene expression through an Sp1 binding site.

The formation of various tissues requires close communication between two groups of cells, epithelial and mesenchymal cells. COUP-TFs are transcription factors which have been shown to have functions in embryonic development. COUP-TFI is expressed mainly in the nervous system, and its targeted deletion leads to defects in the central and peripheral nervous systems. COUP-TFII is highly expressed in the mesenchymal component of the developing organs. A null mutation of COUP-TFII results in the malformation of the heart and blood vessels. From their expression pattern, we proposed that COUP-TFs regulate paracrine signals important for mesenchymal cell-epithelial cell interactions. In order to identify genes regulated by COUP-TF in this process, a rat urogenital mesenchymal cell line was stably transfected with a COUP-TFI expression vector. We found that NGFI-A, a gene with important functions in brain, organ, and vasculature development, has elevated mRNA and protein levels upon overexpression of COUP-TFI in these cells. A study of the promoter region of this gene identified a COUP-TF-responsive element between positions -64 and -46. Surprisingly, this region includes binding sites for members of the Sp1 family of transcription factors but no COUP-TF binding site. Mutations that abolish the Sp1 binding activity also impair the transactivation of the NGFI-A promoter by COUP-TF. Two regions of the COUP-TF molecule are shown to be important for NGFI-A activation: the DNA binding domain and the extreme C terminus of the putative ligand binding domain. The C-terminal region is likely to be important for interaction with coactivators. In fact, the coactivators p300 and steroid receptor activator 1 can enhance the transactivation of the NGFI-A promoter induced by COUP-TFI. Finally, we demonstrated that COUP-TF can directly interact with Sp1. Taken together, these results suggest that NGFI-A is a target gene for COUP-TFs and that the Sp1 family of transcription factors mediates its regulation by COUP-TFs.

Induction of NGFI-B gene expression during T cell activation. Role of protein phosphatases.

mRNA expression of the immediate-early gene NGFI-B was investigated in T cells during the G0/G1 transition as well as throughout the G1 phase. After stimulation of T lymphocytes with Con A or phorbol 12,13 dibutyrate (PDBu), NGFI-B gene expression showed an induction of at least sevenfold within 3 h of stimulation. Twenty-four h later, however, the level of NGFI-B transcripts had fallen to almost basal levels. Activation of the Ca2+ signaling pathway also produced an induction of this gene, although to a lesser extent than the one obtained after protein kinase C activation. Similar transient kinetics of NGFI-B mRNA were also observed after PDBu stimulation of G1 lymphoblasts. However, the induction of NGFI-B by IL-2 is dependent on the presence of cycloheximide. Con A-induced activation of NGFI-B gene expression was not overcome by cyclosporin A or by 8Br-cAMP, but was partially prevented by dexamethasone. In lymphoblasts, okadaic acid caused the induction of NGFI-B gene expression, indicating a role for the serine/threonine protein phosphatases PP1 and PP2A in the regulation of this gene in resting cells. Okadaic acid-induced NGFI-B transcripts were significantly more stable than PDBu-induced NGFI-B mRNA. Thus, the level of NGFI-B transcripts in T cells might be determined by the balance between the activities of several serine/threonine protein kinases and phosphatases. Together, these findings indicate that the transient induction of NGFI-B transcripts is associated with normal lymphocyte activation. Because the mRNA for NGFI-B codes for a zinc-finger DNA-binding protein, these results suggest that NGFI-B participates in transcriptional regulation during T cell activation.

Differential effect of thyroid hormone on NGFI-A gene expression in developing rat brain.

NGFI-A is an immediate early gene that is rapidly activated in quiescent cells by mitogens or in postmitotic neurons after depolarization. We have previously shown that the expression of NGFI-A in the developing rat brain is under the control of thyroid hormone. Now we report, by means of in situ hybridization histochemistry, the differential effect of thyroid hormone on NGFI-A expression in distinct brain regions depending on the developmental stage. NGFI-A messenger RNA (mRNA) content was analyzed in the piriform cortex, striatum, hippocampus, and cerebral cortex of control, hypothyroid, and T3-injected hypothyroid rats at birth and on postnatal days 5 and 15. In the newborn rats, experimental hypothyroidism is associated with reduced levels of NGFI-A mRNA in most of the brain regions studied. On postnatal day 15, the difference in NGFI-A expression between control and hypothyroid rats is less apparent in the striatum or no longer present in the piriform cortex and the hippocampus. In the cerebral cortex, hypothyroidism is associated with reduced levels of NGFI-A mRNA on postnatal day 15. The dentate gyrus is always insensitive to the thyroidal state. Administration of T3 accelerates the recovery of NGFI-A mRNA in 5- and 15-day-old rats. However, in newborn rats, the effect of the hormone is noticeable only in the piriform cortex. We also show that the reduced level of NGFI-A mRNA in hypothyroidism is accompanied by a reduction in the protein level. Convulsions induced by pentylenetetrazole administration resulted in an increased expression of the NGFI-A gene, which is of similar magnitude in control and hypothyroid rats.

NGFI-A gene expression is necessary for T lymphocyte proliferation.

NGFI-A is an immediate early gene, encoding a zinc finger protein, rapidly activated after mitogenic stimulation. NGFI-A gene expression was found to be rapidly and transiently induced after interleukin-2 (IL-2) stimulation of G1 lymphoblasts, as well as during the G0/G1 transition, when stimulated with concanavalin A (ConA). Activation of both Ca2+ and protein kinase C pathways, separately, in quiescent T lymphocytes produced a partial induction of this gene; however, both stimuli together are necessary to obtain a full response. ConA-induced activation of NGFI-A in quiescent cells was inhibited by immunosuppressors. 8-Bromo-cAMP was able to inhibit the expression of this gene in G1 lymphoblasts after IL-2 stimulation, but failed to interfere with the ConA-induced expression in quiescent T lymphocytes. Exposure of T cells to an NGFI-A antisense oligonucleotide blocked the ConA- and IL-2-induced proliferation of the cells, measured as thymidine incorporation and cell number. This inhibition provides direct evidence that the early gene NGFI-A plays a regulatory role in growth control processes of lymphocytes and that its expression is essential for cellular proliferation.

Multiple regulation of S14 gene expression during brown fat differentiation.

S14 is a gene known to be under thyroid hormone control. Its mRNA concentration is very high in lipogenic tissues, and although the precise function of the protein is still unknown, indirect data suggest its implication in triglyceride synthesis. S14 gene expression is up-regulated by thyroid hormone in liver, white adipose tissue, and lactating mammary gland. However, in brown fat, the level of this sequence is increased 3-fold in the hypothyroid animal. We have used primary cultures of brown preadipocytes differentiated to fully mature brown adipocytes to investigate the influence of cellular differentiation and hormonal stimulation on S14 gene expression. Steady state levels of S14 mRNA rose from nondetectable levels in preadipocytes to reach a maximum in fully mature adipocytes. Treatment of brown adipocytes cultures with T3 did induce S14 gene expression. This induction reflects in part a posttranscriptional stabilization of the messenger by T3. Insulin, insulin-like growth factor-I, and inositol phosphate-glycan also increase the level of S14 mRNA. Norepinephrine (NE) plays a major role in the regulation of S14 gene, and 24 h after its addition, NE elicited a 20-fold decrease in mRNA S14 concentrations. An elevated intracellular concentration of cAMP is a strong negative effector of S14 gene expression, and neither NE nor cAMP action is totally overcome by T3. As happens in vivo, glucose is a potent stimulator of S14 mRNA; however, there is a lag time of several hours before its effects can be detected. The increase in S14 gene expression with the maturation stage of the cell suggests an important role for S14 in adipocyte differentiation.

Thyroid hormone up-regulates NGFI-A gene expression in rat brain during development.

NGFI-A is an immediate-early response gene induced by signals that initiate growth and differentiation. Its mRNA encodes a sequence-specific transcriptional activator possibly implicated in the control of brain developmental processes. Due to the essential role of thyroid hormone for a correct brain development, we have now investigated the possible regulation by 3,5,3'-triiodo-L-thyronine (T3) of NGFI-A gene expression during maturation of the central nervous system. Our results indicate that expression of mRNA encoding NGFI-A transcription factor is about 8-fold decreased in the brain of neonatal hypothyroid rats. No changes were seen when hypothyroidism was induced in adult life. T3 treatment increased NGFI-A mRNA within 1 h, suggesting that thyroid hormone effect is likely to be a direct one. These data indicate a strong regulation by thyroid hormone of the expression of the growth factor inducible gene NGFI-A during brain development, making this gene a suitable model to study T3 action in the early developing nervous system.