A tudor domain protein, SIMR-1, promotes siRNA production at piRNA-targeted mRNAs in C. elegans.

piRNAs play a critical role in the regulation of transposons and other germline genes. In Caenorhabditis elegans, regulation of piRNA target genes is mediated by the mutator complex, which synthesizes high levels of siRNAs through the activity of an RNA-dependent RNA polymerase. However, the steps between mRNA recognition by the piRNA pathway and siRNA amplification by the mutator complex are unknown. Here, we identify the Tudor domain protein, SIMR-1, as acting downstream of piRNA production and upstream of mutator complex-dependent siRNA biogenesis. Interestingly, SIMR-1 also localizes to distinct subcellular foci adjacent to P granules and Mutator foci, two phase-separated condensates that are the sites of piRNA-dependent mRNA recognition and mutator complex-dependent siRNA amplification, respectively. Thus, our data suggests a role for multiple perinuclear condensates in organizing the piRNA pathway and promoting mRNA regulation by the mutator complex.

In the biological world, a process known as RNA interference helps cells to switch genes on and off and to defend themselves against harmful genetic material. This mechanism works by deactivating RNA sequences, the molecular templates cells can use to create proteins. Overall, RNA interference relies on the cell creating small RNA molecules that can target and inhibit the harmful RNA sequences that need to be silenced. More precisely, in round worms such as Caenorhabditis elegans, RNA interference happens in two steps. First, primary small RNAs identify the target sequences, which are then combatted by newly synthetised, secondary small RNAs. A number of proteins are also involved in both steps of the process. RNA interference is particularly important to preserve fertility, guarding sex cells against 'rogue' segments of genetic information that could be passed on to the next generation. In future sex cells, the proteins involved in RNA interference cluster together, forming a structure called a germ granule. Yet, little is known about the roles and identity of these proteins. To fill this knowledge gap, Manage et al. focused on the second stage of the RNA interference pathway in the germ granules of C. elegans, examining the molecules that physically interact with a key protein. This work revealed a new protein called SIMR-1. Looking into the role of SIMR-1 showed that the protein is required to amplify secondary small RNAs, but not to identify target sequences. However, it only promotes the creation of secondary small RNAs if a specific subtype of primary small RNAs have recognized the target RNAs for silencing. Further experiments also showed that within the germ granule, SIMR-1 is present in a separate substructure different from any compartment previously identified. This suggests that each substep of the RNA interference process takes place at a different location in the granule. In both C. elegans and humans, disruptions in the RNA interference pathway can lead to conditions such as cancer or infertility. Dissecting the roles of the proteins involved in this process in roundworms may help to better grasp how this process unfolds in mammals, and how it could be corrected in the case of disease.

Distinct regions of the intrinsically disordered protein MUT-16 mediate assembly of a small RNA amplification complex and promote phase separation of Mutator foci.

In C. elegans, efficient RNA silencing requires small RNA amplification mediated by RNA-dependent RNA polymerases (RdRPs). RRF-1, an RdRP, and other Mutator complex proteins localize to Mutator foci, which are perinuclear germline foci that associate with nuclear pores and P granules to facilitate small RNA amplification. The Mutator complex protein MUT-16 is critical for Mutator foci assembly. By analyzing small deletions of MUT-16, we identify specific regions of the protein that recruit other Mutator complex components and demonstrate that it acts as a scaffolding protein. We further determine that the C-terminal region of MUT-16, a portion of which contains predicted intrinsic disorder, is necessary and sufficient to promote Mutator foci formation. Finally, we establish that MUT-16 foci have many properties consistent with a phase-separated condensate and propose that Mutator foci form through liquid-liquid phase separation of MUT-16. P granules, which contain additional RNA silencing proteins, have previously been shown to have liquid-like properties. Thus, RNA silencing in C. elegans germ cells may rely on multiple phase-separated compartments through which sorting, processing, and silencing of mRNAs occurs.

Cdc42 regulates junctional actin but not cell polarization in the Caenorhabditis elegans epidermis.

During morphogenesis, adherens junctions (AJs) remodel to allow changes in cell shape and position while preserving adhesion. Here, we examine the function of Rho guanosine triphosphatase CDC-42 in AJ formation and regulation during Caenorhabditis elegans embryo elongation, a process driven by asymmetric epidermal cell shape changes. cdc-42 mutant embryos arrest during elongation with epidermal ruptures. Unexpectedly, we find using time-lapse fluorescence imaging that cdc-42 is not required for epidermal cell polarization or junction assembly, but rather is needed for proper junctional actin regulation during elongation. We show that the RhoGAP PAC-1/ARHGAP21 inhibits CDC-42 activity at AJs, and loss of PAC-1 or the interacting linker protein PICC-1/CCDC85A-C blocks elongation in embryos with compromised AJ function. pac-1 embryos exhibit dynamic accumulations of junctional F-actin and an increase in AJ protein levels. Our findings identify a previously unrecognized molecular mechanism for inhibiting junctional CDC-42 to control actin organization and AJ protein levels during epithelial morphogenesis.

An instructive role for C. elegans E-cadherin in translating cell contact cues into cortical polarity.

Cell contacts provide spatial cues that polarize early embryos and epithelial cells. The homophilic adhesion protein E-cadherin is required for contact-induced polarity in many cells. However, it is debated whether E-cadherin functions instructively as a spatial cue, or permissively by ensuring adequate adhesion so that cells can sense other contact signals. In Caenorhabditis elegans, contacts polarize early embryonic cells by recruiting the RhoGAP PAC-1 to the adjacent cortex, inducing PAR protein asymmetry. Here we show that the E-cadherin HMR-1, which is dispensable for adhesion, functions together with the α-catenin HMP-1, the p120 catenin JAC-1, and the previously uncharacterized linker PICC-1 (human CCDC85A-C) to bind PAC-1 and recruit it to contacts. Mislocalizing the HMR-1 intracellular domain to contact-free surfaces draws PAC-1 to these sites and depolarizes cells, demonstrating an instructive role for HMR-1 in polarization. Our findings identify an E-cadherin-mediated pathway that translates cell contacts into cortical polarity by directly recruiting a symmetry-breaking factor to the adjacent cortex.

Acrylate functionalized tetraalkylammonium salts with ionic liquid properties.

Acrylate functionalized ionic liquids based on tetraalkylammonium salts with terminal acrylates- and methylacrylates were synthesized. Melting points and ionic conductivity of twenty compounds in six groups were determined. Within one group the effect of three different counterions was investigated and discussed. The groups differ in cationic structure elements because of their functional groups such as acrylate and methacrylate, alkyl residues at the nitrogen and number of quaternary ammonium atoms within the organic cation. The effect of these cationic structure elements has been examined concerning the compiled parameters with a view to qualifying them as components for solid state electrolytes. The newly synthesized ionic liquids were characterized by NMR and FTIR analysis. The exchange of halide ions like bromide as counter ions to weakly coordinating [PF6]⁻, [OTf]⁻ or [TFSI]⁻ reduces the melting points significantly and leads to an ion conductivity of about 10⁻4 S/cm at room temperature. In the case of the dicationic ionic liquid, an ion conductivity of about 10⁻³ S/cm was observed.

Polarization of the C. elegans embryo by RhoGAP-mediated exclusion of PAR-6 from cell contacts.

Early embryos of some metazoans polarize radially to facilitate critical patterning events such as gastrulation and asymmetric cell division; however, little is known about how radial polarity is established. Early embryos of Caenorhabditis elegans polarize radially when cell contacts restrict the polarity protein PAR-6 to contact-free cell surfaces, where PAR-6 regulates gastrulation movements. We have identified a Rho guanosine triphosphatase activating protein (RhoGAP), PAC-1, which mediates C. elegans radial polarity and gastrulation by excluding PAR-6 from contacted cell surfaces. We show that PAC-1 is recruited to cell contacts, and we suggest that PAC-1 controls radial polarity by restricting active CDC-42 to contact-free surfaces, where CDC-42 binds and recruits PAR-6. Thus, PAC-1 provides a dynamic molecular link between cell contacts and PAR proteins that polarizes embryos radially.

BMP4 substitutes for loss of BMP7 during kidney development.

Functional inactivation of divergent bone morphogenetic proteins (BMPs) causes discrete disturbances during mouse development. BMP4-deficient embryos display mesodermal patterning defects at early post-implantation stages, whereas loss of BMP7 selectively disrupts kidney and eye morphogenesis. Whether these distinct phenotypes simply reflect differences in expression domains, or alternatively intrinsic differences in the signaling properties of these ligands remains unknown. To address this issue, we created embryos exclusively expressing BMP4 under control of the BMP7 locus. Surprisingly, this novel knock-in allele efficiently rescues kidney development. These results demonstrate unequivocally that these structurally divergent BMP family members, sharing only minimal sequence similarity can function interchangeably to activate all the essential signaling pathways for growth and morphogenesis of the kidney. Thus, we conclude that partially overlapping expression patterns of BMPs serve to modulate strength of BMP signaling rather than create discrete fields of ligands with intrinsically different signaling properties.

Mice exclusively expressing the short isoform of Smad2 develop normally and are viable and fertile.

Smad2 and Smad3 are closely related effectors of TGFbeta/Nodal/Activin-related signaling. Smad3 mutant mice develop normally, whereas Smad2 plays an essential role in patterning the embryonic axis and specification of definitive endoderm. Alternative splicing of Smad2 exon 3 gives rise to two distinct protein isoforms. The short Smad2(Deltaexon3) isoform, unlike full-length Smad2, Smad2(FL), retains DNA-binding activity. Here, we show that Smad2(FL) and Smad2(Deltaexon3) are coexpressed throughout mouse development. Directed expression of either Smad2(Deltaexon3) or Smad3, but not Smad2(FL), restores the ability of Smad2-deficient embryonic stem (ES) cells to contribute descendants to the definitive endoderm in wild-type host embryos. Mice engineered to exclusively express Smad2(Deltaexon3) correctly specify the anterior-posterior axis and definitive endoderm, and are viable and fertile. Moreover, introducing a human Smad3 cDNA into the mouse Smad2 locus similarly rescues anterior-posterior patterning and definitive endoderm formation and results in adult viability. Collectively, these results demonstrate that the short Smad2(Deltaexon3) isoform or Smad3, but not full-length Smad2, activates all essential target genes downstream of TGFbeta-related ligands, including those regulated by Nodal.

Differential requirements for Smad4 in TGFbeta-dependent patterning of the early mouse embryo.

Genetic and biochemical data have identified Smad4 as a key intracellular effector of the transforming growth factor beta (TGFbeta superfamily of secreted ligands. In mouse, Smad4-null embryos do not gastrulate, a phenotype consistent with loss of other TGFbeta-related signaling components. Chimeric analysis reveals a primary requirement for Smad4 in the extra-embryonic lineages; however, within the embryo proper, characterization of the specific roles of Smad4 during gastrulation and lineage specification remains limited. We have employed a Smad4 conditional allele to specifically inactivate the Smad4 gene in the early mouse epiblast. Loss of Smad4 in this tissue results in a profound failure to pattern derivatives of the anterior primitive streak, such as prechordal plate, node, notochord and definitive endoderm. In contrast to these focal defects, many well-characterized TGFbeta- and Bmp-regulated processes involved in mesoderm formation and patterning are surprisingly unaffected. Mutant embryos form abundant extra-embryonic mesoderm, including allantois, a rudimentary heart and middle primitive streak derivatives such as somites and lateral plate mesoderm. Thus, loss of Smad4 in the epiblast results not in global developmental abnormalities but instead in restricted patterning defects. These results suggest that Smad4 potentiates a subset of TGFbeta-related signals during early embryonic development, but is dispensable for others.

Dietary fish oil prevents asynchronous contractility and alters Ca(2+) handling in adult rat cardiomyocytes.

This study examined the effects of dietary incorporation of n-3 polyunsaturated fatty acids (PUFAs) into cardiac membrane phospholipids on Ca(2+) handling (using Fura-2) and arrhythmic contractility in electrically-stimulated, adult rat ventricular cardiomyocytes. Dietary lipid supplementation with fish oil (FO) for 3 weeks significantly increased the proportion of total n-3 polyunsaturated fatty acids (in particular, docosahexaenoic acid) in ventricular membrane phospholipids compared with a saturated fat (SF) supplemented diet (26.2 +/- 0.9% vs 6.9 +/- 0.9%, respectively, P < 0.001). Cardiomyocytes isolated from the FO group were significantly (P < 0.001) less susceptible to isoproterenol-induced arrhythmic contractile activity compared with the SF group over a range of isoproterenol concentrations. Isoproterenol (0.5 &mgr;M) stimulation increased end-diastolic and systolic [Ca(2+)](i) to a similar extent in both groups. The time constant of Ca(2+) transient decay was significantly increased in the FO group compared with the SF group (98.4 +/- 2.8 ms, n = 8 and 86.9 +/- 2.1 ms, n = 8, P < 0.01, respectively). The effect of dietary n-3 PUFA incorporation into membrane phospholipids was not associated with changes in sarcoplasmic reticulum Ca(2+) content (measured by rapid application of caffeine) or membrane fluidity. The increase in the time constant of decay of Ca(2+) transients following dietary supplementation with FO may indicate altered functioning of the sarcolemmal Na(+)-Ca(2+) exchanger by n-3 PUFA incorporation into membrane phospholipids.

Changes in glycosylation during Drosophila development. The influence of ecdysone on hemomucin isoforms.

To explore a possible signal function of glycodeterminants and the tissue specificity of glycosylation in Drosophila melanogaster, hemomucin, a surface mucin previously isolated from cell lines was studied. It was shown to exist in two glycoforms with molecular masses of 100 and 105 kDa, respectively. The two forms differ by the presence of O-linked galactose, which was only detected in the larger glycoform using the beta-galactose specific peanut agglutinin (PNA). The 105 form was found in cell lines after addition of the cell cycle inhibitor taxol and after induction with ecdysone. When whole animal tissues were analyzed using PNA, dramatic changes were observed during development. We were able to identify a number of proteins, which showed strong PNA-staining in stages with a high ecdysone titer, while virtually no staining was detected in adults. This pattern was specific for PNA and was not observed with any of the other lectins employed in this study. Surprisingly, in contrast to our observation in cell lines, PNA staining of hemomucin was not observed in late third larval and pupal stages, which are known to produce high ecdysone titers. The only organ, in which significant amounts of the 105 form were detected, were the ovaries, where hemomucin is produced in follicle cells during the late phase of oogenesis and subsequently incorporated into the chorion.

Effect of early body weight and moderate dietary restriction on the survival of the Sprague-Dawley rat.

The effects of ad libitum (AL) feeding, moderate dietary restriction (DR), and initial (6-week) and one-year body weights on the two-year survival of the Sprague-Dawley (SD) rat were evaluated. DR-fed rats were given approximately 75 percent of the adult AL food intake. At two years, body weights of DR-fed males and females were approximately 69 and 58 percent of the AL-fed male and female body weights, respectively. The 2-year survival rate was 80 and 74 percent in DR-fed males and females, respectively, and 28 and 38 percent in AL-fed males and females, respectively. This increase in longevity indicates that DR-fed males and females in carcinogenicity studies would have 14.8 and 9.1 additional weeks of exposure in a 2-year period to test compounds, respectively, compared to AL-fed animals. There was no correlation between initial body weight and 2-year survival in DR or AL-fed rats. There was no association between 1-year body weight and 2-year survival among DR-fed rats. However, AL-fed rats with the greatest 1-year body weight had a lower 2-year average survival compared with the lightest AL-fed rats; this trend was statistically significant only in males. Body weights between the first and second years were statistically significantly correlated for both genders and feeding regimens but no correlation was observed between pretest and 2-year body weights. These findings demonstrate that initial body weight is not the determining factor of 2-year survival, but that the total adult food (caloric) intake is important. In conclusion, moderate dietary restriction prevented excessive body weight gain and greatly increased the 2-year survival of the SD rat. Initial body weights did not correlate to 2-year body weight gain and were not a predictive biomarker of 2-year SD rat survival.

Protection by zinc-metallothionein (ZnMT) against cadmium-metallothionein-induced nephrotoxicity.

In contrast to inorganic Cd, acute iv administration of Cd bound to metallothionein (CdMT) concentrates in renal tissue. This uptake of CdMT produces functional and morphological changes in kidneys, similar to those observed after chronic exposure to inorganic Cd. In order to examine the importance of the metal component of MT in the renal uptake of MT, the renal concentration of 35S after administration of [35S]ZnMT and [35S]CdMT was compared. Renal uptake of 35S from both CdMT and ZnMT was very rapid, with peak concentrations observed 15-30 min after administration. 35S in kidneys increased in a dose-dependent manner after administration of various doses of [35S]ZnMT, up to 1.3 mumole MT/kg; however, higher doses did not further increase renal 35S concentrations. A similar saturation of 35S reabsorption was observed for the renal uptake of [35S]CdMT. CdMT produced renal injury with doses as low as 0.26 mumol MT/kg (0.2 mg Cd/kg). In contrast, with a dose of ZnMT as high as 5.12 mumol MT/kg (2 mg Zn/kg), no histopathological changes were observed. Therefore, ZnMT appears to be nontoxic even though ZnMT delivers more MT to the kidney than does CdMT. Because ZnMT and CdMT are apparently handled by the same renal transport mechanism, the effects of ZnMT on 109CdMT renal uptake and nephrotoxicity were determined. One group of mice was given a nephrotoxic dose of 109CdMT (0.51 mumol MT/kg containing 0.4 mg Cd/kg, i.v.), and the other group received an equimolar dose of unlabeled ZnMT 1 min before 109CdMT administration. Renal function was evaluated by measuring urinary glucose and protein excretion, as well as histopathology.(ABSTRACT TRUNCATED AT 250 WORDS)

Discrepancy between the nephrotoxic potencies of cadmium-metallothionein and cadmium chloride and the renal concentration of cadmium in the proximal convoluted tubules.

Acute exposure to inorganic cadmium produces hepatotoxicity, but no renal injury. In contrast, chronic exposure to Cd produces nephrotoxic effects. However, a single injection of cadmium bound to metallothionein (CdMT) can produce nephrotoxicity similar to that seen with chronic exposure to Cd. It is generally thought that CdMT is nephrotoxic because more CdMT than CdCl2 distributes to the kidney. To test this hypothesis, the toxic effects and distribution of Cd were compared after iv injection of CdMT and CdCl2 to mice. CdMT increased urinary excretion of glucose, and protein indicating renal injury. This dysfunction occurred with dosages as low as 0.2 mg Cd/kg. In contrast, renal function was unaltered by CdCl2 administration, even at dosages as high as 3 mg Cd/kg. CdMT distributed almost exclusively to the kidney, whereas CdCl2 preferentially distributed to the liver. However, a high concentration of Cd was also found in the kidneys after CdCl2 administration. In fact, the renal Cd concentration after administration of a high but nonnephrotoxic dose of CdCl2 was equal to or higher than that obtained after injection of nephrotoxic doses of CdMT. Light microscopic autoradiography studies, using 0.3 mg Cd/kg as CdMT and 3 mg Cd/kg as CdCl2, indicated that Cd from CdMT preferentially distributed to the convoluted segments (S1 and S2) of the proximal tubules, whereas Cd from CdCl2 distributed equally to the various segments (convoluted and straight) of the proximal tubules. However, the concentration of Cd at the site of nephrotoxicity, the proximal convoluted tubules, was higher after CdCl2 than after CdMT administration. A higher Cd concentration in both apical and basal parts of the proximal cells was found after CdCl2 than after CdMT administration. Therefore, the reason why CdMT is nephrotoxic and CdCl2 is not nephrotoxic is not due to a higher concentration of Cd in the target cells after CdMT than after CdCl2 administration.

Accumulation and degradation of the protein moiety of cadmium-metallothionein (CdMT) in the mouse kidney.

Of major concern in Cd toxicity is its ability to produce renal damage after chronic exposure in humans and experimental animals. Renal injury affects predominantly the proximal tubules and more specifically the first segments of these tubules. Similar toxic effects to the kidneys are observed after administration of cadmium bound to metallothionein (CdMT). Therefore, CdMT was used in this study as a model to understand the mechanism(s) of Cd nephrotoxicity. It has been recently demonstrated that Cd from CdMT was preferentially taken up by the proximal convoluted tubules. Therefore, the purpose of these studies was to determine if the organic portion of the complex was also accumulated in these tubules. [35S]CdMT prepared from rat liver was administered intravenously to mice at a nonnephrotoxic dose (0.1 mg Cd/kg). The radioactivity in the kidney showed maximum level (80% of the dose) 15 min after the injection. This preferential renal uptake was also observed after administration of various doses of [35S]CdMT. In contrast to the earlier observed persistency of 109Cd in the kidney after 109CdMT administration, 35S disappeared rapidly (with a half-life of approximately 2 hr), and 24 hr after injection of [35S]CdMT, there was very little 35S left in the kidneys. These observations indicate that the protein portion of CdMT is rapidly degraded after renal uptake of CdMT and the released Cd is retained in the kidney. Within the kidney, 35S distributed mainly to the cortex. Light microscopic autoradiography showed that [35S]CdMT preferentially distributed to the proximal convoluted tubule (S1 and S2), which is the site of nephrotoxicity. Within the S1 and S2 segments, a greater distribution of 35S to the apical portion of the cells was observed after administration of both a nonnephrotoxic (0.1 mg Cd/kg) and a nephrotoxic (0.3 mg Cd/kg) dose. 109Cd administered as 109CdMT also distributed to the apical portion of the S1 and S2 cells. Therefore, both the organic (35S) and inorganic (109Cd) portions of CdMT are rapidly and efficiently taken up by the S1 and S2 cells of the proximal tubules, the site of nephrotoxicity. These observations support the concept that CdMT is readily taken up by the proximal tubular cells as a complex, and then its protein portion is rapidly degraded to release Cd that binds permanently to intracellular sites and produces nephrotoxicity.

Renal cadmium deposition and injury as a result of accumulation of cadmium-metallothionein (CdMT) by the proximal convoluted tubules--A light microscopic autoradiography study with 109CdMT.

Chronic, but not acute, exposure to inorganic Cd produces renal damage. However, a single injection of cadmium bound to metallothionein (CdMT) produces renal injury. It is hypothesized that an interorgan redistribution of Cd as CdMT is responsible for the chronic nephrotoxic effect of Cd. To better understand the mechanism(s) of CdMT-induced nephrotoxicity, the intrarenal distribution of 109CdMT was examined. 109CdMT isolated from rat liver was injected into mice at a nonnephrotoxic dose (0.1 mg Cd/kg, iv). The radioactivity in the kidney reached a maximum level (85% of the dose) as early as 30 min following administration and remained essentially constant for up to 7 days after injection. Within the kidney, 109Cd distributed almost entirely to the cortex. Light microscopic autoradiography of the kidney showed that, within the cortex, 109Cd distributed preferentially to the S1 and S2 segments of the proximal convoluted tubules. Within the S1 and S2 segments, the concentration of 109Cd in the basal and apical parts of the cells was similar to that after the nonnephrotoxic dose of CdMT, but after a nephrotoxic dose (0.3 mg Cd/kg) the radioactivity distributed preferentially to the apical portion of the cells. In contrast, light microscopic autoradiography studies with 109CdCl2 revealed that 109Cd was more evenly distributed throughout the proximal tubules. Moreover, after administration of a large dose of inorganic Cd (3 mg Cd/kg), a similar concentration of Cd was found in the convoluted and straight proximal tubules. These data support the hypothesis that CdMT-induced nephrotoxicity might be due, at least in part, to its preferential uptake of CdMT into the S1 and S2 segments of the proximal tubules, the site of Cd-induced nephrotoxicity.

[Circadian variation of the nephrotoxicity induced in rats by bi-daily repeated administration of amikacin]. / Variations temporelles de la néphrotoxicité induite chez le rat par administration bi-quotidienne réitérée d'amikacine.

We have studied the chrononephrotoxicity of amikacin during and after a prolonged treatment in rats. Animals received by intramuscular route a daily dose of 400 mg/kg (in two times) during 7 days at two different times (8.00 - 20.00 and 14.00 - 2.00). Large time-dependent variations in renal injury had been evidenced by several parameters and particularly by enzymuria. This injury is maximal when administration is made at 14.00 - 2.00. These data confirmed our results obtained in previous investigations with single daily injections and evidence that chrononephrotoxicity could permit an optimization of nephrotoxic drugs largely used in clinics.

[Demonstration of seasonal changes of circadian rhythms of amikacin chrononephrotoxicity in rats]. / Mise en évidence des variations saisonnières des rythmes circadiens de la chrononéphrotoxicité de l'amikacine chez le rat.

The present study investigates the chronobiological approach of the amikacin-induced nephrotoxicity in rats treated with a single sublethal dose administered at different times of day. The nephrotoxicity is appreciated by gamma-glutamyl-transferase and N-acetyl-beta-D-glucosaminidase urinary excretion, respectively a brush border and a lysosomal enzyme. These excretions peak out at 14:00 and reach a through at 20:00. In contrast, in a precedent experimentation, in october/november, we evidence gamma-glutamyl-transferase excretion increased at 20:00. So, we evidenced with amikacin not only a circadian but also a seasonal susceptibility in rats.

[Chrononephrotoxicity of amikacin after 7-day chronic poisoning in rats]. / Etude de la chrononéphrotoxicité de l'amikacine après intoxication chronique de sept jours chez le rat.

We have studied the chrononephrotoxicity of amikacin during and after a prolonged treatment in rats. Animals received by intramuscular route a daily dose of 400 mg/kg during 7 days at four different times (08:00, 14:00, 20:00 or 02:00). Large time-dependent variations in renal injury had been evidenced by several parameters and particularly by enzymuria. This injury is maximal when administration is made at 14:00. These data confirmed results obtained in previous investigations. The knowledge of chrononephrotoxicity could permit an optimization of drugs in clinics.

[Chronobiology and renal physiopathology]. / Chronobiologie et physiopathologie rénale.

This review presents our recent knowledge in renal chronobiology, considering physiology, pathology, pharmacology and toxicology. In a first part, are described renal chronophysiological data, pointing out particularly urinary excretion rhythms, largely described for last century. Such physiological observations lead to conclude that renal structures and functions present large temporal variations. Endogenous and exogenous origins of these rhythms are widely discussed. Evidence of such circadian and circannual variations in these renal structures and functions permit to understand why different agents, pathogeneous, toxic or medicamentous, will present time-dependent effects at renal level. So, a second part presents some recent experimental and clinical data in chrononephrology, chronopharmacology and chrononephrotoxicity. Finally, the concept of renal chronesthesy is presented and discussed, in order to explain these temporal variations in renal target susceptibility to different substances acting at this level.