A Multicenter Cohort Study From India of ABO-Incompatible Kidney Transplantation in Post-COVID-19 Patients

BACKGROUND

There is a dearth of data regarding the consequences of ABO-incompatible kidney transplant (ABOiKTx) among post-COVID-19 candidates.

METHODS

The study was designed as a retrospective, multicentric cohort study across 11 sites in India, from August 2020 to December 2021. The data for ABOiKTx conducted for post-COVID-19 candidates were investigated. The primary outcome of biopsy-proven acute rejection was compared with the ABO protocol implemented through Kaplan-Meier analysis. The secondary outcomes were graft loss, patient survival, and infections.

RESULTS

A total of 38 ABOiKTx with candidates of median (interquartile range) age of 38.5 (31.25-47.5) years were performed. Nineteen cases had mild COVID-19 severity, while 9 cases (23.6%) had an oxygen requirement. Six (15.7%) donors also were post-COVID-19. The most common ABO incompatibility reported was A to O in 14 (36.8%) pairs followed by B to O in 10 (26.3%) pairs. The maximum isoagglutinin titer cutoff was 1:2048 and 1:64 for baseline and pretransplant levels, respectively. The median time from COVID-19 infection to surgery was 130 (63.2-183) days. Biopsy-proven acute rejection, graft loss, and mortality were 13.1%, 2.6%, and 2.6%, respectively. The Breslow-Wilcoxon's P value in Kaplan-Meier plots were 0.57 and 0.93 for thymoglobulin-based induction and high dose rituximab-based regimen, respectively. The incidence of reinfection was 2.6%. Two (5.2%) urinary tract infections were reported. No cytomegalovirus or BK polyomavirus infection was reported. The median serum creatinine at 1 year of follow-up was 1.1 (0.8-1.3) mg/dL.

CONCLUSIONS

Our report implies that ABOiKTx in post-COVID-19 candidates can be successfully performed with no major deviation from standard ABO protocol.

Comparison of Thymoglobulin and Grafalon as Induction Agents in Renal Transplantation: A Prospective Study

BACKGROUND

Induction immunosuppression is used to reduce the incidence of acute rejection and prevent delayed graft function. The 2 rabbit anti-thymocyte globulins- thymoglobulin and Grafalon (ATG Fresenius) have been commonly used for induction immunosuppression and treatment of acute rejection in solid organ transplantation. There are very few studies comparing the efficacy and side effects of both the anti-thymocyte globulins therefore this prospective study comparing the 2 types of anti-thymocyte globulins would be of clinical interest.

PATIENTS AND METHODS

This prospective single center study was conducted at Rabindranath Tagore International Institute of Cardiac Sciences, Kolkata, India from April 2019 to June 2020. Sixty-two ABO-compatible renal transplant recipients were included in the study. They were divided in 2 groups of 31 patients each. One group received thymoglobulin (3 mg/kg) and the second group received Grafalon (6 mg/kg). All patients were followed up for 12 months and the 2 groups were compared for incidence of rejections, infections, graft function, patient survival, and graft survival.

RESULTS

There was no significant difference in the incidence of rejections, infective episodes, graft function, posttransplant diabetes mellitus, graft survival and patient survival in thymoglobulin or Grafalon groups. The hematological parameters were similar in both groups at 7 days, 1 month, and 6 months of follow-up. The absolute lymphocyte count was significantly lower in the thymoglobulin group at 12 months posttransplant.

CONCLUSIONS

Thymoglobulin and Grafalon were found to be equivalent in terms of safety and efficacy in short term, with no difference in rejections, infections, graft survival, or patient survival.

A Review of Hyperuricaemia Management with Febuxostat: Dosage Titration, Monitoring and Maintenance

The burden of hyperuricaemia has been steadily increasing both globally and in India. The increasing number of hyperuricaemia- associated co-morbidities, such as Chronic Kidney Disease (CKD), Type 2 Diabetes Mellitus (T2DM), Cardiovascular Diseases (CVD), and hypertension, implies that hyperuricaemia is associated with an increased risk of other chronic conditions or diseases. Despite the availability of several guidelines on hyperuricaemia, recommendations for appropriate titration of Urate Lowering Therapy (ULT) to achieve and maintain appropriate serum Uric Acid (sUA) levels in the Indian context are unclear. Another important challenge is the diagnosis and management of asymptomatic hyperuricaemia with ULT. This review summarises evidence-based discussion and review of literature by expert panellists on hyperuricaemia management with ULT, particularly with Xanthine Oxidase (XO) inhibitors. Based on the discussion, the experts developed a dose-titration algorithm for initiation and long-term management of hyperuricaemia with ULT, comprising febuxostat. The review also highlights some of the current challenges in hyperuricaemia management, which when addressed would benefit primary care physicians across the country for early screening and timely management of hyperuricaemia.

MO992RABBIT ANTITHYMOCYTE GLOBULIN (RATG) AS INDUCTION THERAPY IN INDIAN PATIENTS UNDERGOING RENAL TRANSPLANTATION: CLINICAL EXPERIENCE FROM RISE REGISTRY

Background and Aims

Induction therapy with rabbit anti-thymocyte globulin (rATG) in patients with renal transplantation prevents early graft failure due to immunologic rejection. In India, due to the lack of a robust national transplant registry, limited real-world evidence is available on induction immunosuppression. The RISE study aimed to evaluate the safety and effectiveness of induction immunosuppression using rATG in patients undergoing renal transplantation in India.

Method

In this multicenter, prospective, observational cohort study (CTRI/2017/09/009/009700) adult patients (≥18 years) were included if they were due to have a renal transplant and physicians’ decision to use rATG as an induction therapy was independent of this registry and based on routine clinical practice. Acute rejection and infections over 12 months, graft survival and renal function at the end of 6 and 12 months and safety (adverse events [AEs] and serious AEs [SAEs]) were evaluated over 12 months.

Results

Of the 325 patients enrolled, 314 met the eligibility criteria, 313 patients received at least one dose of rATG (safety population) and 299 patients (evaluable population) received at least one dose of rATG and had no critical protocol deviation (ongoing infection, transplantation date deviation, and ABO incompatibility). Of the 299 donors, 81.3% were live donors and the remaining 18.7% deceased. The mean (SD [standard deviation]) age of participants was 42.8 (11.7) years and 76.3% of patients were men. The cumulative mean (SD) rATG dose was 155.06 (91.12) mg. A total of 23 (7.7%) patients experienced graft rejection; of which 21 (91.3%) patients reported acute rejections; one patient had a hyperacute rejection and another patient had accelerated rejection. These rejections occurred within a median time duration of 0.49 months (range: 0.1 to 7.75 months). The diagnosis of graft rejection was most often done by renal biopsy (n=21, 91.3%; 20 of these patients had acute rejection) and clinical diagnosis in two patients. Cellular rejection was the predominant pathology (n=17, 77.3%), followed by mixed rejection (n=3) and antibody-mediated rejection (n=2). The corresponding mean (SD) time to first graft rejection were 5.45 (1.59) and 10.37 (3.58) months, respectively. The graft survival was 93.3% (n=279) at 6 months and 92.3% (n=276) at 12 months (Figure). The mean (SD) glomerular filtration rate was 64.59 (19.57) and 64.93 (20.26) mL/min/1.73m2 at 6 and 12 months, respectively, suggesting normal post-transplant kidney function. Fifty-three patients (17.7%) reported a total of 74 infections, the most common being bacterial (n=37) followed by viral (n=8) and fungal infections (n=5). Urinary tract infection was the most common site of infection (25 events in 23 patients) followed by sepsis (3 events in 2 patients). A total of 342 AEs were reported in 154 (49.2%) patients during 12 months. The majority of AEs (n=195) were of mild intensity, followed by 124 and 22 events of moderate and severe intensity, respectively. SAEs (n=111) were reported in 56 patients. Pyrexia was the most commonly reported SAE in 10 patients (12 events). A total of seven deaths were reported during the study (acute coronary syndrome, left ventricular dysfunction, neutropenic sepsis, septic shock, sudden sepsis, n=1 each and undetermined, n=2).

Conclusion

The study demonstrated low rejection rate, better survival and function at 6 months and 1 year and an acceptable safety profile of rATG with overall infection incidence less than 18%. Additional follow-up data is warranted to understand factors associated with rejection of graft.

This study was funded by Sanofi, India.

Effect of Different Rituximab Doses on B Cell Count, Anti-A/B Antibody Titer, Graft Function, and Infectious Complications in ABO-Incompatible Renal Transplantation: A Prospective Study

BACKGROUND

ABO-incompatible kidney transplantation (ABOiKT) has been accepted as a viable and cost-effective modality with outcomes comparable to ABO-compatible transplants, but there is a concern regarding higher infectious complications in ABOiKT because of the heightened immunosuppression. The desensitization protocol normally includes antibody removal, B cell depletion by rituximab (RTX), and immunomodulation with intravenous immunoglobulin. Efforts have been made over the years to decrease the dose of RTX in an effort to decrease the infective complications. There is limited literature about the minimum effective dose of RTX, which can cause an effective B cell depletion. This prospective study was designed to correlate the RTX dose with peripheral absolute B cell count, graft function, graft and patient survival, and infective complications.

METHODS

This study included 52 adult ABOiKT recipients with anti-A/B antibody titer up to a maximum of 1:512. The participants were divided into 2 groups of 26 each according to the RTX dosage used: Group A received 100 mg/patient, and Group B received 200 mg/patient. RTX was given 14 days prior to transplant after B cell measurement by flow cytometry. The outcomes were compared after 1 year of follow-up.

RESULTS

Both the dosages effectively depleted the absolute B cell count. Although patient survivals, graft survival, graft function, acute rejection episodes, and post-transplant hospital stay were similar in both groups, infective complications were significantly higher in group B.

CONCLUSION

A low dose (100 mg/patient) of RTX produces effective depletion of B cells while lowering the infective complications in ABOiKT.

An Unusual Case of a Dematiaceous Fungus with an Exclusive Cerebral Involvement After ABO-Incompatible Renal Transplantation

BACKGROUND Cladophialophora carrionii was detected postoperatively in a cerebral space-occupying lesion of a patient who had undergone ABO-incompatible renal transplantation. The infection was successfully treated with oral terbinafine and itraconazole. CASE REPORT An otherwise healthy 46-year-old man underwent ABO-incompatible renal transplantation. Postoperatively, he was hemodynamically stable and the graft was functioning well. Within 2 weeks, the patient developed clinical depression, followed by seizures and left-side hemiparesis. There were no skin findings. Radiological investigation showed 2 space-occupying lesions in the brain parenchyma. The patient's condition improved after partial frontal lobectomy and microsurgical abscess evacuation, with a short course of liposomal amphotericin B and a combination of oral terbinafine and itraconazole. Microbiological examination of the pus showed growth of C. carrionii, which predominantly causes subcutaneous mycoses. CONCLUSIONS It is very rare for melanized fungal infections to cause an exclusively cerebral disease without any skin involvement. Furthermore, among established cases, C. carrionii is a very rarely detected pathogen.

Successful Third Kidney Transplant After Desensitization for Combined Human Leucocyte Antigen (HLA) and ABO Incompatibility: A Case Report and Review of Literature

BACKGROUND In the present era, kidney transplantation across immunological barriers (ABO incompatibility and human leucocyte antigen (HLA) incompatibility) is a successful strategy to provide transplantation to immunologically high-risk patients. The safety and outcome of crossing both ABO and HLA barriers simultaneously in a retransplantation scenario is rarely reported from the developing world. CASE REPORT A 30-year-old female underwent a third living donor kidney transplantation. Her previous 2 transplants being lost to chronic allograft nephropathy. The transplantation was done across a simultaneous blood group as well as HLA incompatibility. The donor was the mother who was blood group B, with the recipient being blood group O. The complement dependent cytotoxicity crossmatch of the pair was negative but the flow cross match for T as well as B lymphocytes was positive. The mean fluorescence intensity value for class I antigens was 6951 and that for class 2 antigens was 7534. The patient underwent a desensitization procedure including rituximab, plasmapheresis and intravenous immunoglobulin pre-transplantation. The pre-transplantation isohemaglutunin titer was <1: 8 and the donor specific antibody against class 1 antigens was <2200 and <770 against class 2 antigens. Induction was done with anti-thymocyte globulin in the dose of 3 mg/kg in 2 divided doses. The patient is maintained on triple immunosuppression with tacrolimus, prednisolone and mycophenolate mofetil. After a follow-up period of 5 months, she maintains a good graft function with serum creatinine of 1.01 mg/dL. CONCLUSIONS With the advances in the desensitizing procedures in the developing world, kidney transplantation across a combined HLA and ABO incompatible barrier can be offered to these highly sensitized patients, even in case of retransplantation.

Comparative analysis of ABO-incompatible kidney transplantation with ABO-compatible transplantation: A single-center experience from Eastern India

This study aimed to compare the outcomes of ABO-incompatible kidney transplantation (ABOiKT) with ABO-compatible kidney transplantation (ABOcKT) in a singlecenter study. A total of 30 consecutive ABOiKT recipients (ABOiKTR) from April 2014 to June 2015 were included in this study. All the patients received rituximab 200 mg/body for B-cell depletion. Plasmapheresis was done for anti-ABO antibody removal. The target anti-ABO titer was kept at <1:8. The outcomes of this group of patients were compared with that of thirty ABOcKT recipients. Both the groups received similar induction therapy with antithymocyte globulin and methylprednisolone. After a follow-up period of one year, the outcomes of both the groups were compared in terms of patient survival, graft survival, graft function, incidence of rejections, infective complications, and duration of posttransplant hospital stay. The patient survival in both the groups of patients was 96.67%. The death-censored graft survival was 96.67% in both the groups. The average serum creatinine level, estimated glomerular filtration rate, incidence of rejections, infective episodes, and posttransplant hospital stay were comparable in both the groups. The outcomes of ABOiKT were comparable with ABOcKT and as such, this modality can expand the living donor pool substantially.

A comparative study of psychosocial determinants and mental well-being in chronic kidney disease patients: A closer look

BACKGROUND

Depressive illness in chronic kidney disease (CKD) is an independent risk factor for morbidity and mortality. The relation between depressive illness and quality of life (QoL) in this vulnerable group is complex. We attempted to study the burden of depressive illness, the QoL in patients of CKD on hemodialysis (HD), and peritoneal dialysis (PD) as well as those who were not on any dialysis but on conservative medical management only.

MATERIALS AND METHODS

Observational study with cross-sectional analytical controlled design.

STATISTICAL METHODS USED

Chi-square statistic or Fisher's exact test for categorical variables and t-test and ANOVA for continuous variables. Correlational analysis was done using Spearman's correlation coefficient. P <0.05 was considered as statistically significant.

RESULTS

Depressive symptoms were present significantly across all 3 groups of CKD patients. Depressive disorder was significantly higher in the HD group. Mean QoL was significantly better in patients of CKD on PD.

DISCUSSION

There is huge hidden burden of depressive symptoms and depressive illness in patients of CKD whether on dialysis or on conservative medical management. The study found significantly higher burden of depressive illness and lower QoL among the HD vis a vis PD patients, even though the majority of our CKD who require dialysis are on HD.

CONCLUSION

Depressive burden is the hidden factor behind poor QoL, poor overall satisfaction as well as treatment outcome in patients of CKD whether or not on dialysis. To address this hidden depressive burden comprehensively, close cooperation between nephrologist and psychiatrist is called for.

Long-Term Consequences of Complex Living Renal Donation: Is It Safe?

INTRODUCTION

As there is a paucity of literature regarding the long-term outcomes of complex living donors, we conducted this study to assess the effect of kidney donation on the complex living kidney donor.

MATERIALS AND METHODS

This retrospective study was conducted in Narayan Health Hospital, Kolkata, Eastern India. The cohort consisted of complex living kidney donors who donated kidneys between the years 2007 and 2012. All donors were 60 years old or older, or were younger than 60 years and had comorbidities like hypertension and obesity. After a minimum follow-up of 5 years, all donors underwent evaluation. Data pertaining to hypertension, new-onset diabetes, body mass index (BMI), estimated glomerular filtration rate (eGFR) and albuminuria, and cardiac events were compared from the time of donation till 5 years post-transplant.

RESULTS AND DISCUSSION

We found a statistically significant increase in blood pressure, number of antihypertensives used, and mean BMI at follow-up. Diabetes mellitus was developed in 22.3% of donors. The mean GFR also decreased significantly at follow-up. There were 42 elderly donors (≥60 years) and 23 ≤ 59 years of age. There was a significant fall of eGFR in both groups, but the percentage fall was similar in both groups. A significant percentage of donors developed proteinuria, the majority being hypertensives.

CONCLUSION

Procurement of kidneys from marginal donors should be done cautiously, and donors should be assessed for morbidity and mortality in the future, as we found a statistically significant deterioration in renal function, blood pressure, and BMI over long-term follow-up.

ABO-Incompatible Renal Transplantation with High Antibody Titer: A Case Report

BACKGROUND Even though renal transplantation across blood groups is not uncommonly practiced nowadays, there is still hesitation regarding ABO-incompatible transplantation with very high baseline antibody titer. In this case report, the outcome of an ABO-incompatible kidney transplant recipient with a high baseline isoagglutinin titer is reported. CASE REPORT The patient was a non-diabetic, 33-year-old man with end-stage renal disease secondary to chronic glomerulonephritis. The only kidney donor available was his mother, who was blood-group incompatible. The patient's blood group was O positive, whereas his mother was B positive. We evaluated him for an ABO-incompatible renal transplant. The baseline anti-B isoagglutinin titer was >1:8196.  With a desensitization protocol of low-dose Rituximab, plasmapheresis, and IVIG, this titer was brought down to 1:32 before transplantation. He successfully underwent renal transplantation across the ABO barrier, and maintains good graft function after 1 year of follow-up.  CONCLUSIONS In the present era, a high baseline isoagglutinin titer is no longer a contraindication for successful kidney transplantation in ABO-incompatible recipient-donor pairs.

Spontaneous Renal Allograft Rupture Caused by Acute Tubular Necrosis: A Case Report and Review of the Literature

Renal allograft rupture (RAR) is a rare but lethal complication of renal transplantation. It potentially threatens graft and patient survival. RAR is frequently associated with acute rejection, but other causes like renal vein thrombosis and acute tubular necrosis have also been observed. Most commonly a graft nephrectomy is required, but graft repair can also be attempted in selected cases to salvage the graft. Herein, we describe a rare case of spontaneous renal allograft rupture in the early posttransplant period due to acute tubular necrosis. A 42-year-old male, living donor renal allograft recipient, experienced RAR on the sixth posttransplant day. Surgical exploration showed two lacerations of 10 cm and 5 cm length at the upper and mid pole of the kidney. Histologically, the graft demonstrated acute tubular injury; no features of humoral or cellular rejection were identified. The successful management of this complication resulted in the salvage of the patient and the graft. This case demonstrates that early diagnosis and prompt treatment of a life-threatening RAR can salvage the graft.

Estimation of the rate of tooth wear in permanent incisors: a cross-sectional digital radiographic study

This study used conventional digital radiography to estimate the rate of tooth wear (TW) of maxillary and mandibular central incisors based on a cross-sectional study design. The crown length of 1239 permanent maxillary and mandibular central incisors from 346 persons (age groups: 10, 25, 40, 55 and 70 years ± 3) were measured by three calibrated dentists. Study teeth were intact incisally, had clearly visible incisal edges and cementoenamel junctions and had natural tooth antagonists. Measures were based on digital radiographic images (N = 666) archived in MiPACS within the electronic health record (axiUm(®)) from the College of Dentistry patient database. Incisor crown length decreased at a linear rate in both arches over the 60 years represented by the age groups. The average crown length for maxillary incisors in the youngest age group was 11.94 mm, which decreased by an average of 1.01 mm by median age 70. For mandibular incisors, the average crown length in the youngest age group was 9.58 mm, which decreased by an average of 1.46 mm in the oldest age group. Males and females showed similar rates of TW. Regardless of age, females demonstrated smaller mean crown height for maxillary incisors than males (P < 0.0001). Measures by the examiners demonstrated good agreement, with an interclass correlation coefficient of 0.869 and an average intra-examiner correlation of 99.5%, based on repeated measurements (n = 100). TW was estimated to average 1.01 mm for maxillary central incisors and 1.46 mm for mandibular central incisors by age 70 years.

Instability and pattern formation in reaction-diffusion systems: A higher order analysis

We analyze the condition for instability and pattern formation in reaction-diffusion systems beyond the usual linear regime. The approach is based on taking into account perturbations of higher orders. Our analysis reveals that nonlinearity present in the system can be instrumental in determining the stability of a system, even to the extent of destabilizing one in a linearly stable parameter regime. The analysis is also successful to account for the observed effect of additive noise in modifying the instability threshold of a system. The analytical study is corroborated by numerical simulation in a standard reaction-diffusion system.

Disruption of the Crithidia fasciculata KAP1 gene results in structural rearrangement of the kinetoplast disc

The mitochondrial DNA (kinetoplast DNA) in trypanosomatids exists as a highly organized nucleoprotein structure with the DNA consisting of thousands of interlocked circles. Four H1 histone-like proteins (KAP1, 2, 3 and 4) are associated with the kinetoplast DNA in the trypanosomatid Crithidia fasciculata. We have disrupted both alleles of the KAP1 gene in this diploid protozoan and shown that expression of the KAP1 protein is eliminated. The mutant strain is viable but has substantial rearrangement of the kinetoplast structure. Expression of the KAP1 protein from an episome restored expression of the KAP1 protein in the mutant strain and also restored a normal kinetoplast structure. These studies provide evidence that the KAP1 protein is involved in kinetoplast DNA organization in vivo but is nonessential for cell viability.

Noise properties of stochastic processes and entropy production

Based on a Fokker-Planck description of external Ornstein-Uhlenbeck noise and cross-correlated noise processes driving a dynamical system we examine the interplay of the properties of noise processes and the dissipative characteristic of the dynamical system in the steady state entropy production and flux. Our analysis is illustrated with appropriate examples.

Characterization of the Crithidia fasciculata mRNA cycling sequence binding proteins

The Crithidia fasciculata cycling sequence binding protein (CSBP) binds with high specificity to sequence elements in several mRNAs that accumulate periodically during the cell cycle. Mutations in these sequence elements abolish both cycling of the mRNA and binding of CSBP. Two genes, CSBPA and CSBPB, encoding putative subunits of CSBP have been cloned and were found to be present in tandem on the same DNA molecule and to be closely related. CSBPA and CSBPB are predicted to encode proteins with sizes of 35.6 and 42.0 kDa, respectively. Both CSBPA and CSBPB proteins have a predicted coiled-coil domain near the N terminus and a novel histidine and cysteine motif near the C terminus. The latter motif is conserved in other trypanosomatid species. Gel sieving chromatography and glycerol gradient sedimentation results indicate that CSBP has a molecular mass in excess of 200 kDa and an extended structure. Recombinant CSBPA and CSBPB also bind specifically to the cycling sequence and together can be reconstituted to give an RNA gel shift similar to that of purified CSBP. Proteins in cell extracts bind to an RNA probe containing six copies of the cycling sequence. The RNA-protein complexes contain both CSBPA and CSBPB, and the binding activity cycles in near synchrony with target mRNA levels. CSBPA and CSBPB mRNA and protein levels show little variation throughout the cell cycle, suggesting that additional factors are involved in the cyclic binding to the cycling sequence elements.

Analytical and numerical investigation of escape rate for a noise driven bath

We consider a system-reservoir model where the reservoir is modulated by an external noise. Both the internal noise of the reservoir and the external noise are stationary, Gaussian, and are characterized by arbitrary decaying correlation functions. Based on a relation between the dissipation of the system and the response function of the reservoir driven by external noise, we numerically examine the model using a full bistable potential to show that one can recover the turn-over features of the usual Kramers' dynamics when the external noise modulates the reservoir rather than the system directly. We derive the generalized Kramers' rate for this nonequilibrium open system. The theoretical results are verified by numerical simulation.

RNA primer removal and gap filling on a model minicircle replication intermediate

Replication of kinetoplast DNA minicircles in Crithidia fasciculata occurs by a unidirectional mechanism involving continuous synthesis of one strand (L strand) and discontinuous synthesis of the complementary strand (H strand). L-strands are initiated by RNA priming at alternate origins (A and B) resulting in daughter molecules with a single nick or gap in the L strand at either ori A or ori B. Some of the gapped molecules contain ribonucleotides at the 5' side of the gap. We have investigated the ability of recombinant forms of kinetoplast replication proteins, DNA polymerase beta and structure specific endonuclease 1, to repair gaps in a model minicircle substrate. Structure specific endonuclease 1 was shown to efficiently remove all ribonucleotides from the 5' side of the model substrate by stepwise cleavage of the RNA primer. Polymerase beta was then able to extend the 3' terminus of the gap to yield a nicked molecule capable of covalent joining by a DNA ligase. These results demonstrate that the nuclease and polymerase enzymes present at antipodal protein complexes flanking the kinetoplast disk are capable of complete RNA primer removal and subsequent gap filling of newly synthesized minicircle L strands.

The Crithidia fasciculata RNH1 gene encodes both nuclear and mitochondrial isoforms of RNase H

The Crithidia fasciculata RNH1 gene encodes an RNase H, an enzyme that specifically degrades the RNA strand of RNA-DNA hybrids. The RNH1 gene is contained within an open reading frame (ORF) predicted to encode a protein of 53.7 kDa. Previous work has shown that RNH1 expresses two proteins: a 38 kDa protein and a 45 kDa protein which is enriched in kinetoplast extracts. Epitope tagging of the C-terminus of the RNH1 gene results in localization of the protein to both the kinetoplast and the nucleus. Translation of the ORF beginning at the second in-frame methionine codon predicts a protein of 38 kDa. Insertion of two tandem stop codons between the first ATG codon and the second in-frame ATG codon of the ORF results in expression of only the 38 kDa protein and the protein localizes specifically to the nucleus. Mutation of the second methionine codon to a valine codon prevents expression of the 38 kDa protein and results in exclusive production of the 45 kDa protein and localization of the protein only in the kinetoplast. These results suggest that the kinetoplast enzyme results from processing of the full-length 53.7 kDa protein. The nuclear enzyme appears to result from translation initiation at the second in-frame ATG codon. This is the first example in trypanosomatids of the production of nuclear and mitochondrial isoforms of a protein from a single gene and is the only eukaryotic gene in the RNase HI gene family shown to encode a mitochondrial RNase H.

Fluctuation-dissipation relationship in chaotic dynamics

We consider a general N-degree-of-freedom dissipative system that exhibits chaotic behavior. Based on a Fokker-Planck description associated with the dynamics, we establish that the drift and the diffusion coefficients can be related through a set of stochastic parameters that characterize the steady state of the dynamical system in a way similar to the fluctuation-dissipation relation in nonequilibrium statistical mechanics. The proposed relationship is verified by numerical experiments on a driven double-well system.

Identification of cis and trans elements involved in the cell cycle regulation of multiple genes in Crithidia fasciculata

Transcripts of several DNA replication genes, including the RPA1 and TOP2 genes, encoding the large subunit of nuclear replication protein A and the kinetoplast topoisomerase II, accumulate periodically during the cell cycle in the trypanosomatid Crithidia fasciculata. An octamer consensus sequence, CAUAGAAG, present in the 5' untranslated regions (UTR) of these mRNAs is required for periodic accumulation of the TOP2 and RPA1 transcripts and also for binding of a nuclear factor(s) to the 5' UTR RNAs of these genes. We show here that insertion of multiple (six) copies of this octamer sequence (6x octamer) into the 5' UTR of a reporter gene confers periodic accumulation on its transcript. Competition experiments and UV cross-linking studies show that the 6x octamer RNA and TOP2 5' UTR RNA bind to the same nuclear factor(s). Single-nucleotide substitutions in the 6x octamer that abolish the RNA gel shift also prevent cyclic accumulation of the reporter gene transcript. A protein termed cycling element binding protein, purified by affinity chromatography using 6x octamer RNA as a ligand, binds to RNAs containing wild-type octamers and not to those with mutant octamers. These results define a small sequence element in C. fasciculata mRNAs required for their cell cycle regulation and report the identification and purification of a putative regulatory protein that binds specifically to these elements.

The kinetoplast structure-specific endonuclease I is related to the 5' exo/endonuclease domain of bacterial DNA polymerase I and colocalizes with the kinetoplast topoisomerase II and DNA polymerase beta during replication

The mitochondrial DNA (kinetoplast DNA) of the trypanosomatid Crithidia fasciculata has an unusual structure composed of minicircles and maxicircles topologically interlocked into a single network and organized in a disc-shaped structure at the base of the flagellum. We previously purified a structure-specific endonuclease (SSE1), based on its RNase H activity, that is enriched in isolated kinetoplasts. The endonuclease gene has now been cloned, sequenced, and found to be closely related to the 5' exonuclease domain of bacterial DNA polymerase I proteins. Although the protein does not contain a typical mitochondrial leader sequence, the enzyme is shown to colocalize with a type II DNA topoisomerase and a DNA polymerase beta at antipodal sites flanking the kinetoplast disc. Cell synchronization studies with an epitope-tagged construct show that the localization of the endonuclease to the antipodal sites varies in a cell cycle-dependent manner similar to that of the DNA polymerase beta [Johnson, C. E. & Englund, P. T. (1998) J. Cell Biol. 143, 911-919]. Immunofluorescent localization of SSE1 to the antipodal sites is only observed during kinetoplast replication. Together, these results suggest a point of control for kinetoplast DNA replication through the regulation of the availability of DNA replication proteins and a possible role for the antipodal sites in removal of RNA primers and the repair of gaps in newly replicated minicircles.

A structure-specific DNA endonuclease is enriched in kinetoplasts purified from Crithidia fasciculata

The mitochondrial DNA (kinetoplast DNA) of the trypanosomatid Crithidia fasciculata consists of minicircles and maxicircles topologically interlocked in a single network per cell. Individual minicircles replicate unidirectionally from either of two replication origins located 180 degrees apart on the minicircle DNA. Initiation of minicircle leading-strand synthesis involves the synthesis of an RNA primer which is removed in the last stage of replication. We report here the purification to near homogeneity of a structure-specific DNA endo-nuclease based on the RNase H activity of the enzyme on a poly(rA).poly(dT) substrate. RNase H activity gel analysis of whole cell and kinetoplast extracts shows that the enzyme is enriched in kinetoplast fractions. The DNA endonuclease activity of the enzyme is specific for DNA primers annealed to a template strand and requires an unannealed 5' tail. The enzyme cleaves 3' of the first base paired nucleotide releasing the intact tail. The purified enzyme migrates as a 32 kDa protein on SDS gels and has a Stoke's radius of 21.5 A and a sedimentation coefficient of 3.7 s, indicating that the protein is a monomer in solution with a native molecular mass of 32.4 kDa. These results suggest that the enzyme may be involved in RNA primer removal during minicircle replication.

Nuleclear extracts of Crithidia fasciculata contain a factor(s) that binds to the 5'-untranslated regions of TOP2 and RPA1 mRNAs containing sequences required for their cell cycle regulation

The Crithidia fasciculata replication protein A gene, RPA1, and topoisomerase II gene, TOP2, encode proteins involved in the replication of nuclear and mitochondrial DNA, respectively. Transcripts of both genes accumulate periodically during the cell cycle and attain their maximum levels just before S phase. Octamer consensus sequences within the 5'-untranslated region (UTR) of both genes have been shown to be necessary for cycling of these transcripts. Using a gel retardation assay, we show here that nuclear extracts of C. fasciculata contain a protein factor(s) that binds specifically to RNA from 5'-UTRs of TOP2 and RPA1 genes. In addition, mutations in the consensus octamer sequence abolish binding to the RNA in both cases. Ultraviolet cross-linking using a radiolabeled TOP2 5'-UTR probe identified proteins with apparent molecular masses of 74 and 37 kDa in the RNA-protein complex. Nuclear extracts prepared from synchronized cells show that the binding activity varies during the cell cycle in parallel with TOP2 and RPA1 mRNA levels. These results suggest that the cell cycle regulation of the mRNA levels of trypanosomatid DNA replication genes may be mediated by binding of specific proteins to conserved sequences in the 5'-UTR of their transcripts.

The Crithidia fasciculata KAP1 gene encodes a highly basic protein associated with kinetoplast DNA

The Crithidia fasciculata KAP1 gene encodes a small basic protein (p21) associated with kinetoplast DNA. The p21 protein has a nine amino acid cleavable presequence closely related to those of several other proteins targeted to the kinetoplast and binds non-specifically to kinetoplast minicircle DNA. The p21 protein also has a calculated pI of 13 with two amino acids (lysine and alanine) accounting for more than 50% of the residues and with 25 out of 28 lysine residues contained in the C-terminal half of the protein. Immunolocalization of p21 shows that the protein is found exclusively in the kinetoplast with a localization distinctly different from the antipodal localization of kinetoplast DNA topoisomerase and DNA polymerase. The KAP11 gene is a single copy gene and the KAP1 mRNA is present at a constant level throughout the cell cycle. This highly basic protein may play a role in the condensation or segregation of the kinetoplast DNA.

Tandem arrangement of two genes encoding kinetoplast-associated H1 histone-like proteins

Crithidia fasciculata proteins p18 and p17 are associated with kinetoplast DNA and are encoded by genes KAP2 and KAP3, respectively. Polymerase chain reaction (PCR) amplification using primers within the coding sequences of each gene revealed that the KAP2 and KAP3 genes are linked on the same chromosomal DNA and are separated by a 1.8 kb intergenic region containing several long homopolymer tracts. The KAP2 gene has a 3'UTR of more than 1.1 kb or almost three times as long as the KAP2 coding sequence. Several restriction enzyme polymorphisms in this region of the chromosome are the result of sequence differences between the two alleles of the KAP2 gene. The predicted amino-acid sequences of alleles KAP2-1 and KAP2-2 differ by three non-conservative amino acid substitutions in the highly basic carboxyl tail of the protein and suggest that the protein products could have different physical and biological properties. The KAP2 and KAP3 genes have different patterns of mRNA expression during the cell cycle with the KAP3 transcript varying periodically during the cell cycle in the same manner as transcripts of several kinetoplast and nuclear DNA replication genes.

Cell cycle regulation of RPA1 transcript levels in the trypanosomatid Crithidia fasciculata

Transcripts of both mitochondrial and nuclear DNA replication genes accumulate periodically during the cell cycle in Crithidia fasciculata. An octameric consensus sequence with a conserved hexameric core was found previously to be required for cycling of the TOP2 transcript, encoding the mitochondrial DNA topoisomerase. We show here that the rate of synthesis of the p51 protein, the large subunit of nuclear replication protein-A encoded by the RPA1 gene, varies during the cell cycle in parallel with RPA1 mRNA level. Plasmids expressing a truncated form of RPA1 (Delta RPA1 ) were used to identify cis elements required for cycling of the Delta RPA1 transcript. Sequences within the RPA1 5'-untranslated region (UTR) were found to be necessary for cycling of the Delta RPA1 transcript. These sequences also function when transposed 3'of the Delta RPA1 coding sequence. A 121 bp fragment of this sequence can confer cycling on a heterologous transcript, but is inactivated when two consensus octamers within the sequence are mutated. Mutation of these two octamers in the full-length 5'-UTR ofDelta RPA1 is insufficient to abolish cycling of the mRNA unless three additional octamers having single base changes within the hexameric core are also mutated. Thus, common octameric sequence elements are involved in periodic accumulation of both the TOP2 and RPA1 transcripts.

Sequences within the 5' untranslated region regulate the levels of a kinetoplast DNA topoisomerase mRNA during the cell cycle

Gene expression in trypanosomatids appears to be regulated largely at the posttranscriptional level and involves maturation of mRNA precursors by trans splicing of a 39-nucleotide miniexon sequence to the 5' end of the mRNA and cleavage and polyadenylation at the 3' end of the mRNA. To initiate the identification of sequences involved in the periodic expression of DNA replication genes in trypanosomatids, we have mapped splice acceptor sites in the 5' flanking region of the TOP2 gene, which encodes the kinetoplast DNA topoisomerase, and have carried out deletion analysis of this region on a plasmid-encoded TOP2 gene. Block deletions within the 5' untranslated region (UTR) identified two regions (-608 to -388 and -387 to -186) responsible for periodic accumulation of the mRNA. Deletion of one or the other of these sequences had no effect on periodic expression of the mRNA, while deletion of both regions resulted in constitutive expression of the mRNA throughout the cell cycle. Subcloning of these sequences into the 5' UTR of a construct lacking both regions of the TOP2 5' UTR has shown that an octamer consensus sequence present in the 5' UTR of the TOP2, RPA1, and DHFR-TS mRNAs is required for normal cycling of the TOP2 mRNA. Mutation of the consensus octamer sequence in the TOP2 5' UTR in a plasmid construct containing only a single consensus octamer and that shows normal cycling of the plasmid-encoded TOP2 mRNA resulted in substantial reduction of the cycling of the mRNA level. These results imply a negative regulation of TOP2 mRNA during the cell cycle by a mechanism involving redundant elements containing one or more copies of a conserved octamer sequence within the 5' UTR of TOP2 mRNA.

Nucleus-encoded histone H1-like proteins are associated with kinetoplast DNA in the trypanosomatid Crithidia fasciculata

Kinetoplast DNA (kDNA), the mitochondrial DNA of trypanosomatids, consists of thousands of minicircles and 20 to 30 maxicircles catenated into a single large network and exists in the cell as a highly organized compact disc structure. To investigate the role of kinetoplast-associated proteins in organizing and condensing kDNA networks into this disc structure, we have cloned three genes encoding kinetoplast-associated proteins. The KAP2, KAP3, and KAP4 genes encode proteins p18, p17, and p16, respectively. These proteins are small basic proteins rich in lysine and alanine residues and contain 9-amino-acid cleavable presequences. Proteins p17 and p18 are closely related to each other, with 48% identical residues and carboxyl tails containing almost exclusively lysine, alanine, and serine or threonine residues. These proteins have been expressed as Met-His6-tagged recombinant proteins and purified by metal chelate chromatography. Each of the recombinant proteins is capable of compacting kDNA networks in vitro and was shown to bind preferentially to a specific fragment of minicircle DNA. Expression of each of these proteins in an Escherichia coli mutant lacking the HU protein rescued a defect in chromosome condensation and segregation in the mutant cells and restored a near-normal morphological appearance. Proteins p16, p17, and p18 have been localized within the cell by immunofluorescence methods and appear to be present throughout the kDNA. Electron-microscopic immunolocalization of p16 shows that p16 is present both within the kDNA disc and in the mitochondrial matrix at opposite edges of the kDNA disc. Our results suggest that nucleus-encoded H1-like proteins may be involved in the organization and segregation of kDNA networks in trypanosomatids.

Disruption of the Crithidia fasciculata RNH1 gene results in the loss of two active forms of ribonuclease H

Both prokaryotic and eukaryotic cells contain multiple forms of ribonuclease H, a ribonuclease that specifically degrades the RNA strand of RNA-DNA hybrids and which has been implicated in the processing of initiator RNAs and in the removal of RNA primers from Okazaki fragments. The Crithidia fasciculata RNH1 gene encodes an RNase H and was shown to be a single-copy gene in this diploid trypanosomatid. The RNH1 gene has been disrupted by targeted gene disruption using hygromycin or G418 drug-resistance cassettes. Major active forms of RNase H (38 and 45 kDa) were observed on activity gels of extracts of wild-type cells or cells in which one allele of RNH1 was disrupted. Both the 38 and 45 kDa activities were absent in extracts of cells in which both alleles of RNH1 were disrupted indicating that both forms of the C.fasciculata RNase H are encoded by the RNH1 gene.

Periodic expression of nuclear and mitochondrial DNA replication genes during the trypanosomatid cell cycle

In trypanosomatids, DNA replication in the nucleus and in the single mitochondrion (or kinetoplast) initiates nearly simultaneously, suggesting that the DNA synthesis (S) phases of the nucleus and the mitochondrion are coordinately regulated. To investigate the basis for the temporal link between nuclear and mitochondrial DNA synthesis phases the expression of the genes encoding DNA ligase I, the 51 and 28 kDa subunits of replication protein A, dihydrofolate reductase and the mitochondrial type II topoisomerase were analyzed during the cell cycle progression of synchronous cultures of Crithidia fasciculata. These DNA replication genes were all expressed periodically, with peak mRNA levels occurring just prior to or at the peak of DNA synthesis in the synchronized cultures. A plasmid clone (pdN-1) in which TOP2, the gene encoding the mitochondrial topoisomerase, was disrupted by the insertion of a NEO drug-resistance cassette was found to express both a truncated TOP2 mRNA and a truncated topoisomerase polypeptide. The truncated mRNA was also expressed periodically coordinate with the expression of the endogenous TOP2 mRNA indicating that cis elements necessary for periodic expression are contained within cloned sequences. The expression of both TOP2 and nuclear DNA replication genes at the G1/S boundary suggests that regulated expression of these genes may play a role in coordinating nuclear and mitochondrial S phases in trypanosomatids.

Isolation of the genes encoding the 51-kilodalton and 28-kilodalton subunits of Crithidia fasciculata replication protein A

The genes encoding the 51-kilodalton subunit (p51) and the 28-kilodalton subunit (p28) of replication protein A (RP-A), designated CfaRPA1 and CfaRPA2 respectively, were cloned from the trypanosomatid Crithidia fasciculata by screening a genomic DNA library in the expression vector lambda gt11 with antibodies raised against purified C. fasciculata RP-A. CfaRPA1 has a single open reading frame encoding a polypeptide of 467 amino acids and a molecular mass of 52.0 kDa. The predicted p51 polypeptide has sequence similarity to the corresponding subunits from human, Xenopus laevis, and Saccharomyces cerevisiae, but is lacking a segment of approximately 20 kDa from its amino terminus, accounting for its smaller molecular weight when compared to the large subunits of RP-A from these other organisms. CfaRPA1 contains a zinc-finger motif that is also found in the RP-A large subunits from human, frog, and yeast. CfaRPA2 contains a single large open reading frame encoding a polypeptide of 258 amino acids and a molecular mass of 27.5 kDa. The predicted polypeptide has significant sequence similarity to the middle subunit of RP-A from human cells, mouse cells, and the budding yeast S. cerevisiae. Northern hybridization analysis of polyadenylated RNA from C. fasciculata indicates that both cloned genes are expressed as polyadenylated transcripts. CfaRPA1 hybridized with a 2.30-kb transcript and CfaRPA2 hybridized with a 1.44-kb transcript.

Functional complementation of an Escherichia coli ribonuclease H mutation by a cloned genomic fragment from the trypanosomatid Crithidia fasciculata

A gene designated Cfa RNH1 has been cloned by complementation of an RNase H deficiency in an Escherichia coli rnhA mutant by using a genomic DNA library from the trypanosomatid Crithidia fasciculata. The encoded RNase H is predicted to have 494 amino acid residues and a molecular mass of 53.7 kDa. The carboxyl half of the protein is homologous to the 155-residue E. coli RNase HI (41% identity) and the 166-residue Saccharomyces cerevisiae RNase HI (33% identity). The recombinant protein has been purified as a six-histidine-tagged fusion protein by metal chelate chromatography and was shown to have RNase H activity. Antibodies against the recombinant protein recognize proteins of approximately 65 kDa and 56 kDa on Western blots of C. fasciculata extracts. These results demonstrate the feasibility of cloning trypanosome genes by complementation of appropriate E. coli mutants with genomic DNA libraries.

Isolation of proteins associated with kinetoplast DNA networks in vivo

Kinetoplast DNA (kDNA), the mitochondrial DNA of trypanosomes, is a highly condensed disc-shaped network of catenated DNA circles consisting of maxicircles, the equivalent of conventional mitochondrial DNA, and several thousand smaller circular DNAs termed minicircles. Upon cell lysis, kDNA expands, giving rise to a two-dimensional network of catenated circles with an overall diameter close to that of the whole cell. To identify proteins associated with the condensed form of kDNA in the cell, proteins were reversibly crosslinked to kDNA in whole cells of Crithidia fasciculata by formaldehyde treatment. Crosslinked networks were purified and found to retain a condensed structure which becomes fully expanded upon proteinase K treatment or reversal of the crosslinks by heating at 65 degrees C. Five low molecular weight proteins released from the kDNA by heat treatment were purified by polyacrylamide gel electrophoresis and their amino-terminal sequences were determined. PCR amplification and sequence analysis of cDNA sequences between these amino-terminal sequences and the miniexon (spliced leader) sequence present at the 5' end of all C. fasciculata mRNAs predicts the presence of 9-amino acid presequences with features characteristic of mitochondrial presequences on three of the proteins. Two of these proteins are lysine-rich basic proteins. These findings suggest that basic proteins may play a role in the condensation of kDNA in the kinetoplast and that these proteins are imported into the kinetoplast by a mechanism involving a cleavable presequence.