The mutated human gene encoding hepatocyte nuclear factor 1beta inhibits kidney formation in developing Xenopus embryos.

The transcription factor hepatocyte nuclear factor 1beta (HNF1beta) is a tissue-specific regulator that also plays an essential role in early development of vertebrates. In humans, four heterozygous mutations in the HNF1beta gene have been identified that lead to early onset of diabetes and severe primary renal defects. The degree and type of renal defects seem to depend on the specific mutation. We show that the frameshift mutant P328L329fsdelCCTCT associated with nephron agenesis retains its DNA-binding properties and acts as a gain-of-function mutation with increased transactivation potential in transfection experiments. Expression of this mutated factor in the Xenopus embryo leads to defective development and agenesis of the pronephros, the first kidney form of amphibians. Very similar defects are generated by overexpressing in Xenopus the wild-type HNF1beta, which is consistent with the gain-of-function property of the mutant. In contrast, introduction of the human HNF1beta mutant R137-K161del, which is associated with a reduced number of nephrons with hypertrophy of the remaining ones and which has an impaired DNA binding, shows only a minor effect on pronephros development in Xenopus. Thus, the overexpression of both human mutants has a different effect on renal development in Xenopus, reflecting the variation in renal phenotype seen with these mutations. We conclude that mutations in human HNF1beta can be functionally characterized in Xenopus. Our findings imply that HNF1beta not only is an early marker of kidney development but also is functionally involved in morphogenetic events, and these processes can be investigated in lower vertebrates.

The embryonic expression of the tissue-specific transcription factor HNF1alpha in Xenopus: rapid activation by HNF4 and delayed induction by mesoderm inducers.

The tissue-specific transcription factor HNF1alpha is expressed in kidney, liver, intestine and stomach of Xenopus. We show that the HNF1alpha gene is transcriptionally activated at the onset of zygotic gene transcription and that this transcription is maintained throughout development. Ectodermal explants of blastulae (animal caps) express HNF1alpha mRNA upon stimulation with the mesoderm inducers activin A and BMP4 as well as on overexpression of Smad2 and Smad1, the corresponding members of the intracellular TGF-beta signal transducers, respectively. Beside these factors that mediate their response through serine/threonine kinase receptors, bFGF, which acts via tyrosine kinase receptors, leads to HNF1alpha expression, too. These embryonic inducers result in a delayed appearance of HNF1alpha mRNA, excluding a direct activation of HNF1alpha. In contrast, the maternally expressed nuclear receptors HNF4alpha and HNF4beta activate the initial HNF1alpha transcription, since overexpression of HNF4 leads to a rapid expression of HNF1alpha mRNA in animal caps. Similarly, in entire neurulae HNF4 overexpression results in increased HNF1alpha transcription. Therefore, we assume that the initial activation is dependent on maternal HNF4alpha and HNF4beta transcription factors whereas HNF1alpha induction by growth factors reflects the property of these factors to induce the differentiation of mesodermal and entodermal cell types expressing HNF1alpha.

Patterning the expression of a tissue-specific transcription factor in embryogenesis: HNF1 alpha gene activation during Xenopus development.

Tissue-specific transcription factors play an essential role in establishing cell identity during development. We review our knowledge of the molecular events involved in the activation of the gene encoding the tissue-specific transcription factor HNF1 alpha (LFB1). The available data suggest that the maternal factors OZ-1, HNF4 alpha and HNF4 beta act as initial activators of the HNF1 alpha promoter. We present evidence suggesting that the mesoderm-inducing factor activin A plays a critical role by acting through the HNF4 binding site of the HNF1 alpha promoter. The activity of this embryonic morphogen seems to form a gradient opposing the distribution of the maternal HNF4 proteins that are concentrated at the animal pole of the egg. After zygotic gene transcription the HNF1 alpha-related transcription factor HNF1 beta accumulates faster than HNF1 alpha itself and thus is likely to contribute to the activation of the HNF1 alpha transcription via the HNF1 binding site. The cofactor of the HNF1 proteins (DCoH) is present throughout development and thus cannot limit the activation potential of HNF1 alpha in early development. Our results provide a detailed description of setting up the expression pattern of a tissue-specific transcription factor during embryogenesis.

Intravenous infusions of nifedipine: an alternative for the prevention of hypertension in eye surgery under local anesthesia.

In order to control critical rises of blood pressure during the peri-operative period in elderly hypertensive patients, the effectiveness of a continuous intravenous infusion of nifedipine was studied. In a double blind study, patients (n = 60) who underwent eye surgery under local anesthesia were divided randomly into three groups. Patients who were found to have 200 > SBP > 160 and 120 > DBP > 90 mmHg as the previous day of surgery, as well as patients who did not receive any anti-hypertensive treatment regimen during the last week before surgery, were selected. Five min before performing local anesthesia, a continuous infusion of nifedipine at two different rates of 0.65 mg/h and 1.25 mg/h, was administered in groups A and B respectively, whereas group C received a placebo. SBP, DBP and HR were recorded every 5 min. for an hour. Statistically significant differences among the profiles of the three groups were found. The control group had a higher SBP/DBP. None of the groups, showed significant changes in HR. In conclusion, the intravenous infusion of nifedipine in a dose 1.25 mg/h, seems to control the hypertensive phases of blood pressure, without dropping to any unduly low level, risking undesirable side effects in elderly hypertensive patients during perioperative period.

Fluctuations in serum magnesium levels during total intravenous anaesthesia with propofol.

Forty patients who underwent eye surgery under total intravenous anaesthesia with propofol where investigated in order to determine the fluctuations of serum magnesium levels during anaesthesia. Six blood samples were taken before anaesthesia, after induction, 1 hour later, 2 hours later, after recovery, and 24 hours after surgery. In the same time intervals, systolic and diastolic blood pressure, heart rate and temperature were recorded. The results showed a statistically significant decrease in serum magnesium levels during anaesthesia. No correlations between this decrease and the fluctuations of blood pressure, heart rate or temperature were found. These results indicate that there is a shift of magnesium into the tissue stores due to the state of anaesthesia, possibly by a direct effect of the anaesthetic agents on the cell membrane itself. Further investigation is needed with other techniques and agents employed in general anaesthesia.

Prophylactic effects of intravenous magnesium on hypertensive emergencies after cataract surgery. A new contribution to the pharmacological use of magnesium in anaesthesiology.

The pharmacological effects of magnesium sulphate heptahydrate (MgSO4.7H2O) on hypertensive patients during the perioperative period were used, to control critical rises of blood pressure. This double-blind study included 40 hypertensive elderly patients, who underwent eye surgery under local anaesthesia; they were divided into two groups (A and B) of 20 patients each. An intravenous dose of 4g MgSO4.7H2O was given to group. A, while group B, which was used as a control group, was given to a placebo. All patients were premedicated with 10 mg oral diazepam 1.5 h before the operation. Systolic and diastolic blood pressure, heart rate and ECG were monitored for 1 h. None of the patients who received MgSO4.7H2O showed any ECG disturbances. Systolic and diastolic blood pressure, as well as heart rate, fluctuated outside the critical range, whereas in the control group an increase of blood pressure was noted which was treated with other anti hypertensive drugs. The results indicated that parenteral administration of MgSO4.7H2O in hypertensive patients before surgery stabilized blood pressure fluctuations outside the critical range, without causing the pressure to fall to a level that might risk undesirable side effects during eye surgery under local anaesthesia.