Defining Priorities for Future Research: Results of the UK Kidney Transplant Priority Setting Partnership

BACKGROUND

It has been suggested that the research priorities of those funding and performing research in transplantation may differ from those of end service users such as patients, carers and healthcare professionals involved in day-to-day care. The Kidney Transplant Priority Setting Partnership (PSP) was established with the aim of involving all stakeholders in prioritising future research in the field.

METHODS

The PSP methodology is as outlined by the James Lind Alliance. An initial survey collected unanswered research questions from patients, carers and clinicians. Duplicate and out-of-scope topics were excluded and the existing literature searched to identify topics answered by current evidence. An interim prioritisation survey asked patients and professionals to score the importance of the remaining questions to create a ranked long-list. These were considered at a final consensus workshop using a modified nominal group technique to agree a final top ten.

RESULTS

The initial survey identified 497 questions from 183 respondents, covering all aspects of transplantation from assessment through to long-term follow-up. These were grouped into 90 unanswered "indicative" questions. The interim prioritisation survey received 256 responses (34.8% patients/carers, 10.9% donors and 54.3% professionals), resulting in a ranked list of 25 questions that were considered during the final workshop. Participants agreed a top ten priorities for future research that included optimisation of immunosuppression (improved monitoring, choice of regimen, personalisation), prevention of sensitisation and transplanting the sensitised patient, management of antibody-mediated rejection, long-term risks to live donors, methods of organ preservation, induction of tolerance and bioengineering of organs. There was evidence that patient and carer involvement had a significant impact on shaping the final priorities.

CONCLUSIONS

The final list of priorities relates to all stages of the transplant process, including access to transplantation, living donation, organ preservation, post-transplant care and management of the failing transplant. This list of priorities will provide an invaluable resource for researchers and funders to direct future activity.

Antisense Activity across the Nesp Promoter is Required for Nespas-Mediated Silencing in the Imprinted Gnas Cluster

Macro long non-coding RNAs (lncRNAs) play major roles in gene silencing in inprinted gene clusters. Within the imprinted Gnas cluster, the paternally expressed Nespas lncRNA downregulates its sense counterpart Nesp. To explore the mechanism of action of Nespas, we generated two new knock-in alleles to truncate Nespas upstream and downstream of the Nesp promoter. We show that Nespas is essential for methylation of the Nesp differentially methylated region (DMR), but higher levels of Nespas are required for methylation than are needed for downregulation of Nesp. Although Nespas is transcribed for over 27 kb, only Nespas transcript/transcription across a 2.6 kb region that includes the Nesp promoter is necessary for methylation of the Nesp DMR. In both mutants, the levels of Nespas were extraordinarily high, due at least in part to increased stability, an effect not seen with other imprinted lncRNAs. However, even when levels were greatly raised, Nespas remained exclusively cis-acting. We propose Nespas regulates Nesp methylation and expression to ensure appropriate levels of expression of the protein coding transcripts Gnasxl and Gnas on the paternal chromosome. Thus, Nespas mediates paternal gene expression over the entire Gnas cluster via a single gene, Nesp.

Gene Dosage Effects at the Imprinted Gnas Cluster

Genomic imprinting results in parent-of-origin-dependent monoallelic gene expression. Early work showed that distal mouse chromosome 2 is imprinted, as maternal and paternal duplications of the region (with corresponding paternal and maternal deficiencies) give rise to different anomalous phenotypes with early postnatal lethalities. Newborns with maternal duplication (MatDp(dist2)) are long, thin and hypoactive whereas those with paternal duplication (PatDp(dist2)) are chunky, oedematous, and hyperactive. Here we focus on PatDp(dist2). Loss of expression of the maternally expressed Gnas transcript at the Gnas cluster has been thought to account for the PatDp(dist2) phenotype. But PatDp(dist2) also have two expressed doses of the paternally expressed Gnasxl transcript. Through the use of targeted mutations, we have generated PatDp(dist2) mice predicted to have 1 or 2 expressed doses of Gnasxl, and 0, 1 or 2 expressed doses of Gnas. We confirm that oedema is due to lack of expression of imprinted Gnas alone. We show that it is the combination of a double dose of Gnasxl, with no dose of imprinted Gnas, that gives rise to the characteristic hyperactive, chunky, oedematous, lethal PatDp(dist2) phenotype, which is also hypoglycaemic. However PatDp(dist2) mice in which the dosage of the Gnasxl and Gnas is balanced (either 2∶2 or 1∶1) are neither dysmorphic nor hyperactive, have normal glucose levels, and are fully viable. But PatDp(dist2) with biallelic expression of both Gnasxl and Gnas show a marked postnatal growth retardation. Our results show that most of the PatDp(dist2) phenotype is due to overexpression of Gnasxl combined with loss of expression of Gnas, and suggest that Gnasxl and Gnas may act antagonistically in a number of tissues and to cause a wide range of phenotypic effects. It can be concluded that monoallelic expression of both Gnasxl and Gnas is a requirement for normal postnatal growth and development.

Loss of Gnas imprinting differentially affects REM/NREM sleep and cognition in mice

It has been suggested that imprinted genes are important in the regulation of sleep. However, the fundamental question of whether genomic imprinting has a role in sleep has remained elusive up to now. In this work we show that REM and NREM sleep states are differentially modulated by the maternally expressed imprinted gene Gnas. In particular, in mice with loss of imprinting of Gnas, NREM and complex cognitive processes are enhanced while REM and REM-linked behaviors are inhibited. This is the first demonstration that a specific overexpression of an imprinted gene affects sleep states and related complex behavioral traits. Furthermore, in parallel to the Gnas overexpression, we have observed an overexpression of Ucp1 in interscapular brown adipose tissue (BAT) and a significant increase in thermoregulation that may account for the REM/NREM sleep phenotypes. We conclude that there must be significant evolutionary advantages in the monoallelic expression of Gnas for REM sleep and for the consolidation of REM-dependent memories. Conversely, biallelic expression of Gnas reinforces slow wave activity in NREM sleep, and this results in a reduction of uncertainty in temporal decision-making processes.

Survivorship of Conserve® Plus monoblock metal-on-metal hip resurfacing sockets: radiographic midterm results of 580 patients

Resurfacing systems use press-fit, monoblock, cobalt chrome alloy acetabular sockets because of the material's ability to withstand stresses while accommodating a large femoral head. Despite the widespread use of these types of sockets for both hip resurfacing and total hip replacement, there is a paucity of literature assessing the outcomes of these cups in particular. The 10 year survivorship of the Conserve® Plus monoblock acetabular component used in this study was 98.3% with small pelvic osteolytic lesions suspected in only 2.3%. This study highlights the excellent radiographic survivorship profile of the Conserve® Plus socket.

Uncoupling antisense-mediated silencing and DNA methylation in the imprinted Gnas cluster

There is increasing evidence that non-coding macroRNAs are major elements for silencing imprinted genes, but their mechanism of action is poorly understood. Within the imprinted Gnas cluster on mouse chromosome 2, Nespas is a paternally expressed macroRNA that arises from an imprinting control region and runs antisense to Nesp, a paternally repressed protein coding transcript. Here we report a knock-in mouse allele that behaves as a Nespas hypomorph. The hypomorph mediates down-regulation of Nesp in cis through chromatin modification at the Nesp promoter but in the absence of somatic DNA methylation. Notably there is reduced demethylation of H3K4me3, sufficient for down-regulation of Nesp, but insufficient for DNA methylation; in addition, there is depletion of the H3K36me3 mark permissive for DNA methylation. We propose an order of events for the regulation of a somatic imprint on the wild-type allele whereby Nespas modulates demethylation of H3K4me3 resulting in repression of Nesp followed by DNA methylation. This study demonstrates that a non-coding antisense transcript or its transcription is associated with silencing an overlapping protein-coding gene by a mechanism independent of DNA methylation. These results have broad implications for understanding the hierarchy of events in epigenetic silencing by macroRNAs.

Genomic imprinting is a process resulting in expression of genes according to parental origin. Some imprinted genes are expressed when paternally derived and others when maternally derived. Thus imprinted genes are monoallelically expressed and one copy has to be silenced. There is evidence that some long non-coding RNAs, acting in cis, have a role in silencing. We investigated the role of Nespas, a gene for a non-coding RNA that is only expressed from the paternally derived chromosome in the Gnas cluster and runs antisense to its sense counterpart, Nesp. Expression of Nespas is associated with silencing of Nesp and a repressive methylation mark on the Nesp DNA. We generated a Nespas mutant with reduced levels of activity and showed that it down-regulated its sense counterpart Nesp, in the absence of a DNA methylation mark, but in the presence of an altered chromatin mark. We conclude that Nespas can repress Nesp by a mechanism independent of DNA methylation, by modulating a chromatin mark.

Collagen dysregulation in the dermis of the Sagg/+ mouse: a loose skin model

The Sagg/+ mouse is an ethylnitrosourea-derived mutant with a dermal phenotype similar to some of the subtypes of Ehlers-Danlos syndrome (EDS) and cutis laxa. The dermis of the Sagg/+ mouse has less dense and more disorganized collagen fibers compared to controls. The size of extracted Type I dermal collagen was the same as that observed in normal skin; however, more collagen could be extracted from Sagg/+ skin, which also showed decreased collagen content and decreased steady-state levels of alpha1(I), alpha2(I), alpha1(V), and alpha2(V) procollagen mRNAs. The biomechanical properties of Sagg/+ skin were significantly decreased relative to normal skin. However, there were no significant differences in the quantities of the major collagen cross-links, that is, dehydrohydroxylysinonorleucine and dehydrohistidinohydroxymerodesmosine between Sagg/+ and normal skin. Electron microscopic evaluation of Sagg/+ skin indicated that the mutation interferes with the proper formation of collagen fibrils and the data are consistent with a mutation in Type V collagen leading to haploinsufficiency with the formation of two sub-populations of collagen fibrils, one normal and one with irregular shape and a larger diameter. Further study of this novel mutation will allow the identification of new mechanisms involved in the regulation of normal and pathologic collagen gene expression.

Identification of an imprinting control region affecting the expression of all transcripts in the Gnas cluster

Genomic imprinting results in allele-specific silencing according to parental origin. Silencing is brought about by imprinting control regions (ICRs) that are differentially marked in gametogenesis. The group of imprinted transcripts in the mouse Gnas cluster (Nesp, Nespas, Gnasxl, Exon 1A and Gnas) provides a model for analyzing the mechanisms of imprint regulation. We previously identified an ICR that specifically regulates the tissue-specific imprinted expression of the Gnas gene. Here we identify a second ICR at the Gnas cluster. We show that a paternally derived targeted deletion of the germline differentially methylated region (DMR) associated with the antisense Nespas transcript unexpectedly affects both the expression of all transcripts in the cluster and methylation of two DMRs. Our results establish that the Nespas DMR is the principal ICR at the Gnas cluster and functions bidirectionally as a switch for modulating expression of the antagonistically acting genes Gnasxl and Gnas. Uniquely, the Nespas DMR acts on the downstream ICR at exon 1A to regulate tissue-specific imprinting of the Gnas gene.

A cis-acting control region is required exclusively for the tissue-specific imprinting of Gnas

Genomic imprinting brings about allele-specific silencing according to parental origin. Silencing is controlled by cis-acting regulatory regions that are differentially marked during gametogenesis and can act over hundreds of kilobases to silence many genes. Two candidate imprinting control regions (ICRs) have been identified at the compact imprinted Gnas cluster on distal mouse chromosome 2, one at exon 1A upstream of Gnas itself and one covering the promoters for Gnasxl and the antisense Nespas (ref. 8). This imprinted cluster is complex, containing biallelic, maternally and paternally expressed transcripts that share exons. Gnas itself is mainly biallelically expressed but is weakly paternally repressed in specific tissues. Here we show that a paternally derived targeted deletion of the germline differentially methylated region at exon 1A abolishes tissue-specific imprinting of Gnas. This rescues the abnormal phenotype of mice with a maternally derived Gnas mutation. Imprinting of alternative transcripts, Nesp, Gnasxl and Nespas (ref. 13), in the cluster is unaffected. The results establish that the differentially methylated region at exon 1A contains an imprinting control element that specifically regulates Gnas and comprises a characterized ICR for a gene that is only weakly imprinted in a minority of tissues. There must be a second ICR regulating the alternative transcripts.

Urinary retinol binding protein in Indo-Asian patients with idiopathic interstitial nephritis

BACKGROUND

Idiopathic interstitial nephritis (IIN) is common in the UK Indo-Asian population. Lack of systemic involvement and unremarkable urinalysis on stick testing suggest that it may underlie some cases of end-stage renal failure of undetermined cause. If IIN is diagnosed early, prompt initiation of treatment can improve long-term outcome.

AIMS

To investigate whether urinary retinol binding protein (RBP) is elevated more commonly than urinary albumin in IIN, and might be useful in the early detection of renal disease in Indo-Asian patients.

DESIGN

Preliminary observational study

METHODS

We measured urinary RBP and urinary albumin in 19 Indo-Asian patients in whom a renal biopsy had shown IIN, 10 of whom had already been treated with corticosteroids at the time of specimen collection. A further 28 Indo-Asian patients with glomerular disease, and six with normal light-microscopic renal biopsy, were assessed in parallel.

RESULTS

Urinary RBP/creatinine ratio (RCR) was elevated in all 19 cases of IIN, compared to 12/19 in whom the albumin/creatinine ratio (ACR) was elevated. Elevated urinary RBP was thus significantly more common than albuminuria in this group (p<0.01). Twelve of the 19 cases also satisfied the criteria for tubular proteinuria. RCR was elevated to >30 times the upper limit of normal in 7/9 who had not previously received corticosteroids, of whom four had normal ACR; none had ACR >5 times the upper limit of normal.

DISCUSSION

These data suggest that measurement of urinary RBP should be explored as an adjunct to albuminuria, if screening for renal disease in the Indo-Asian population is contemplated.

Biochemical and recessive visible specific locus responses of C3H/HeH to fractionated, acute radiation

The recessive visible specific locus test has been widely used for many years to investigate the genetic effects of radiation in mice. We devised an electrophoretic-specific locus test so that biochemical mutations leading to alterations in the activity or amount of four enzymes and proteins, as well as charge changes could be detected. We measured the yield of recessive visible and electrophoretic mutations in the same experiment so that a direct comparison of mutation incidence could be made. Dominant visible mutations were also scored. The recessive visible specific locus response of male C3H/HeH to a fractionated dose of 3 + 3 Gy X-irradiation separated by 24 h was similar to that previously reported for the F1 hybrid widely used in mutagenesis studies, and other strains. The response of C3H/HeH was significantly greater for the recessive visible mutations than for the biochemical mutations, supporting the contention that the recessive visible loci are more mutable than others. Mutational analysis of some of the mutants showed that the lesions ranged from a very deletion (30% of chromosome 14 deleted) to a point mutation. The number of loci scored in the electrophoretic test has been reassessed, and it is now considered that six, not four were scored, and this has implications for the calculation of the doubling dose.

A morphologic, biochemical, and biomechanical assessment of short-term effects of osteochondral autograft plug transfer in an animal model

PURPOSE

The objective of this study was to assess the short-term changes that occur after an osteochondral autograft plug transfer from the femoral trochlea to the medial femoral condyle in a goat model.

TYPE OF STUDY

Articular cartilage repair animal study.

METHODS

Six adult male goats were used in this study. Two 4.5-mm osteochondral plugs were transferred from the superolateral femoral trochlea to 2 recipient sites in the central portion of the medial femoral condyle for a survival period of 12 weeks. Postmortem, the global effects of the procedure were assessed by gross morphologic inspection and by analyzing the synovial DNA for inflammatory response. The recipient sites were also evaluated histologically and biomechanically. Metabolic activity was determined by (35)SO(4) uptake, and viability was assessed using a live/dead stain and by confocal laser microscopy.

RESULTS

There was no evidence of significant gross morphologic or histologic changes in the operative knee as a result of the osteochondral donor or recipient sites. The patella, tibial plateau, and medial meniscus did not show any increased degenerative changes as a result of articulating against the donor or recipient sites of the osteochondral autografts. Analysis of synovial DNA revealed no inflammatory response. Biomechanically, 6- to 7-fold greater stiffness was noted in the cartilage of the transferred plugs compared with the control medial femoral condyle. Furthermore, on histologic examination, the healing subchondral bone interface at the recipient site had increased density. Glycosaminoglycan synthesis as determined by (35)SO(4) uptake was upregulated in the transplanted cartilage plug relative to the contralateral control, showing a repair response at the site of implantation. And finally, confocal microscopy showed 95% viability of the transferred plugs in the medial femoral condyle region.

CONCLUSIONS

Our findings demonstrate the ability to successfully transfer an osteochondral autograft plug with maintenance of chondrocyte cellular viability. The transferred cartilage is stiffer than the control medial femoral condyle cartilage, and there is concern regarding the increased trabecular mass in the healing subchondral plate, but these do not result in increased degenerative changes of the opposing articular surfaces in the short term.

The spatial and temporal expression pattern of Nesp and its antisense Nespas, in mid-gestation mouse embryos

We describe the spatiotemporal expression pattern of Nesp, and its antisense transcript, Nespas. We found non-complementary expression of these two oppositely imprinted transcripts during mouse embryogenesis, in a number of forming embryonic structures. Nesp expression was primarily seen in the somites and vasculature, whereas Nespas was mainly detected in the progress zone, mesenchyme and ectoderm of the limb, and the neural tube.

Localisation of the imprinted gene neuronatin, Nnat, confirms and refines the location of a second imprinting region on mouse chromosome 2

Nine regions on six mouse autosomes are subject to imprinting and uniparental inheritance of any one of these regions results in mice with phenotypic anomalies. So far on distal Chromosome (Chr) 2 there is a unique imprinting region between 2H3 and 2H4 associated with two behavioural disorders and neonatal lethality. A maternally imprinted gene, Nnat, has been identified which is expressed in the nervous system and maps to distal Chr 2. Nnat has been excluded as a candidate for either or both the behavioural phenotypes as it lies proximal to the 2H3-2H4 imprinting region. Here we have mapped Nnat to band 2H1 which is at least 18 Mb proximal to the previously described imprinting region. It maps close to agouti, some alleles of which show differential expression according to parental origin. The localisation of Nnat to band H1 confirms and refines the map location of a second imprinting region on mouse Chr 2.

Injuries of the thoracolumbar spine associated with restraint use in head-on motor vehicle accidents

Many authors have described spinal and bodily injuries associated with seat belt use. However, most reports have focused primarily on lap seat belts and resultant flexion-distraction injuries. This retrospective chart review studies the relation between the specific type of restraint or air bag and the resultant thoracolumbar spinal injury subtype and associated bodily injuries. The charts of 221 patients who had sustained thoracolumbar fractures in motor vehicle accidents during a 10-year period were reviewed, and 37 patients were identified whose accidents were clearly described as a frontal collision and whose specific form of restraint was recorded. Among the 15 patients who used a shoulder strap and lap belt device (three-point restraint), 12 patients sustained burst fractures (80%) compared with 4 of the 14 patients (28.6%) restrained with lap seat belts alone. Life-threatening intraabdominal injuries occurred in 57.1% of lap-belted victims and in 26.7% of patients who used three-point restraints, and the character of these injuries also differed. No patients in an automobile in which an air bag deployed sustained major associated bodily injuries. Among restrained occupants of head-on motor vehicle accidents who have sustained a thoracolumbar fracture, patients using lap belts are more likely to sustain the classic flexion-distraction injury patterns, whereas patients using three-point restraints may sustain a higher incidence of burst fractures. In addition, three-point restraints are associated with a decreased risk of intraabdominal injury compared with lap seat belts.

An imprinted transcript, antisense to Nesp, adds complexity to the cluster of imprinted genes at the mouse Gnas locus

The Gnas locus in distal mouse chromosome (Chr) 2 is emerging as a complex genomic region. It contains three imprinted genes in the order Nesp-Gnasxl-Gnas. Gnas encodes a G protein alpha-subunit, and Nesp and Gnasxl encode proteins of unknown function expressed in neuroendocrine tissue. Together, these genes form a single transcription unit because transcripts of Nesp and Gnasxl are alternatively spliced onto exon 2 of Gnas. Nesp and Gnasxl are expressed from opposite parental alleles, with Nesp encoding a maternal-specific transcript and Gnasxl encoding a paternal-specific transcript. We now identify a further imprinted transcript in this cluster. Reverse transcription-PCR analysis of Nesp expression in 15. 5-days-postcoitum embryos carrying only maternal or paternal copies of distal Chr 2 revealed an isoform that is exclusively paternally, rather than maternally, expressed. Strand-specific reverse transcription-PCR showed that this form is an antisense transcript. The existence of a paternally expressed antisense transcript was confirmed by Northern blot analysis. The sequence is contiguous with genomic sequence downstream of Nesp and encompasses Nesp exons 1 and 2 and an intervening intron. We propose that Nespas is an additional control element in the imprinting region of mouse distal Chr 2; it adds further complexity to the Gnas-imprinted gene cluster.

Management of ureteral strictures in renal transplants by antegrade balloon dilatation and temporary internal stenting

PURPOSE

To evaluate the efficacy of percutaneous balloon dilatation and temporary internal stenting in the treatment of transplant ureteral strictures.

METHODS

Nine patients presenting with obstructed renal transplants were treated by antegrade nephrostomy insertion, ureteroplasty, and temporary internal stenting. Following stent removal, patients were divided into two groups for analysis according to whether the obstruction occurred less than (group A) or more than (group B) 3 months following transplantation.

RESULTS

All procedures were technically successful. In group A (n = 6), all patients were successfully treated by one or two dilatations with stenting. In group B (n = 3), two patients were successfully treated by one dilatation with stenting. Overall, eight patients (89%) have had their primary or secondary stent removed successfully at a mean interval of 97.5 days after insertion, and remain well at a mean follow-up interval of 22 months.

CONCLUSION

Balloon dilatation and temporary internal stenting is a useful method for treating transplant ureteral strictures.

Genetic and functional analysis of neuronatin in mice with maternal or paternal duplication of distal Chr 2

Functional differences between parental genomes are due to differential expression of parental alleles of imprinted genes. Neuronatin (Nnat) is a recently identified paternally expressed imprinted gene that is initially expressed in the rhombomeres and pituitary gland and later more widely in the central and peripheral nervous system mainly in postmitotic and differentiating neuroepithelial cells. Nnat maps to distal chromosome (Chr) 2, which contains an imprinting region that causes morphological abnormalities and early neonatal lethality. More detailed mapping analysis of Nnat showed that it is located between the T26H and T2Wa translocation breakpoints which is, surprisingly, proximal to the reported imprinting region between the T2Wa and T28H translocation breakpoints, suggesting that there may be two distinct imprinting regions on distal chromosome 2. To investigate the potential role of Nnat, we compared normal embryos with those which were PatDp.dist2.T26H (paternal duplication/maternal deficiency of chromosome 2 distal to the translocation breakpoint T26H) and MatDp.dist2.T26H. Expression of Nnat was detected in the PatDp.dist2.T26H embryos, where both copies of Nnat are paternally inherited, and normal embryos but no expression was detected in the MatDp.dist2.T26H embryos with the two maternally inherited copies. The differential expression of Nnat was supported by DNA methylation analysis with the paternally inherited alleles being unmethylated and the maternal alleles fully methylated. Although experimental embryos appeared grossly similar phenotypically in the structures where expression of Nnat was detected, differences in folding of the cerebellum were observed in neonates, and other more subtle developmental or behavioral effects due to gain or loss of Nnat cannot be ruled out.

Cloning and characterization of a sialidase from the murine histocompatibility-2 complex: low levels of mRNA and a single amino acid mutation are responsible for reduced sialidase activity in mice carrying the Neu1a allele

The Neu1 locus, in the S region of the murine histocompatibility-2 complex, regulates the sialic acid content of several liver lysosomal enzymes. Three alleles, Neu1a, Neu1b, and Neu1c, have been described on the basis of differential sialylation of the enzyme liver acid phosphatase. The Neu1a allele occurs in a small number of mouse strains, e.g., SM/J and is associated with sialidase deficiency. We recently described G9, a sialidase gene in the human major histocompatibility complex (Milner et al. (1997) J. Biol. Chem., 272, 4549-4558), and we now report the characterization of the equivalent gene in mouse. The protein product of the murine G9 gene is 409 amino acids in length and is 83% identical to its human orthologue. Expression of the murine G9 protein in insect cells has confirmed that it is a sialidase, with optimal activity at pH 5. To elucidate the basis of sialidase deficiency in mouse strains carrying the Neu1a allele, we have sequenced the G9 coding regions from mice carrying the three Neu1 alleles and hence defined the amino acid sequence characteristic of each allotype. Of particular interest is a Leu-209 to Ile mutation that is unique to the Neu1a allotype and is associated with reductions in sialidase activity of approximately 68% and approximately 88% compared to the Neu1b and Neu1c allotypes, respectively, when these three protein variants are expressed in insect cells. Additional factors, such as differential expression, may also influence the activities of the Neu1 allotypes in vivo. We have observed that the level of G9 mRNA is substantially reduced in mice carrying the Neu1a allele compared to the Neu1b (85-95% reduction) and Neu1c (approximately 70% reduction) alleles.

The mouse chromosome 7 distal imprinting domain maps to G-bands F4/F5

Mouse Chromosome (Chr) 7 distal to band F3 on the physical map is known to be subject to imprinting, maternal duplication (MatDp) of the region leading to a late embryonic lethality, while paternal duplication (PatDp) causes death in utero before 11.5 dpc. Using a new mouse reciprocal translocation T(7;11)65H to produce MatDp for distal Chr 7, we have mapped the region subject to imprinting more precisely to bands 7F4/F5 on the cytogenetic map. Fluorescence in situ hybridization (FISH) studies on mitotic and meiotic chromosomes of a T65H heterozygote show that the imprinted gene Igf2 is located in the same region. This was confirmed by the finding that embryos with MatDp of bands 7F4/F5 did not express Igf2. We suggest that other members of the imprinted domain containing Igf2, namely Mash2, H19, Ins2, and p57(K1P2), are also located in 7F4/F5 and that some or all of these genes may be responsible for the two imprinting lethalities seen with MatDp and PatDp for this region.

Transplantation immunology

The success of transplantation is such that it is now the treatment of choice for many of those requiring renal replacement therapy. The use of other solid organs, including liver, pancreas, heart and lung, continues to progress. This article reviews some recent advances in our understanding of the immunological response to alloantigen and xenoantigen.

Thirteen genes (Cebpb, E2f1, Tcf4, Cyp24, Pck1, Acra4, Edn3, Kcnb1, Mc3r, Ntsr, Cd40, Plcg1 and Rcad) that probably lie in the distal imprinting region of mouse chromosome 2 are not monoallelically expressed

Seven imprinted genes are currently known in the mouse but none have been identified yet in the distal imprinting region of mouse Chromosome (Chr) 2, a region which shows striking linkage conservation with human chromosome 20q13. Both maternal duplication/paternal deficiency and its reciprocal for distal Chr 2 lead to mice with abnormal body shapes and behavioural abnormalities. We have tested a number of candidate genes, that are either likely or known to lie within the distal imprinting region, for monoallelic expression. These included 3 genes (Cebpb, E2f1 and Tcf4) that express transcription factors, 2 genes (Cyp24 and Pck1) that are involved in growth, 5 genes (Acra4, Edn3, Kcnb1, Mc3r and Ntsr) where a defect could lead to neurological and probably behavioural problems, and 3 genes (Cd40, Plcg1 and Rcad) that are less obvious candidates but sequence information was available for designing primers to test their expression. On/off expression of each gene was tested by reverse transcription-polymerase chain reaction (RT-PCR) analysis of RNA extracted from tissues of mice with maternal duplication/paternal deficiency and its reciprocal for the distal region of Chr 2. None of the 13 genes is monoallelically expressed in the appropriate tissues before and shortly after birth which suggests that these genes are not imprinted later in development. This study has narrowed down the search for imprinted genes, and valuable information on which genes have been tested for on/off expression is provided. Since there is considerable evidence of conservation of imprinting between mouse and human, we would predict that the 13 genes are not imprinted in human. Five of the genes: E2f1, Tcf4, Kcnb1, Cd40 and Rcad, have not yet been mapped in human. However, because of the striking linkage conservation observed between mouse Chr 2 and human chromosome 20, we would expect these genes to map on human chromosome 20q13.

Mapping studies of the distal imprinting region of mouse chromosome 2

The known limits of the distal imprinting region of mouse Chromosome (Chr) 2 are defined by the breakpoints of the translocations T(2;8)2Wa, (T2Wa), and T(2;16)28H, (T28H), in distal H3, and proximal H4 respectively. We have shown that T2Wa and T(2;4)1Go, (T1Go), which has a breakpoint in central H3 map close to a, non-agouti. Ada, adenosine deaminase, lies very near the proximal boundary and Ra, ragged, maps very close to the distal boundary, and is less than 0.2 cM from wasted, wst. From the current data Ada can be taken as the proximal, and Ra as the distal gene marker of the imprinting region on the linkage map. From consensus maps twenty three other markers, including fourteen genes, lie between Ada and Ra, some of which may be useful in investigations of imprinting. Of the markers included in the study reported here, four, Ada, ls, lethal spotting, Ra and wst lie or probably lie within the region but none display any evidence of imprinting. We suggest that recombination frequency is elevated in distal Chr 2, because in none of the crosses could the most closely linked marker be ordered in relation to the translocation breakpoint due to the high frequency of double crossovers.

Adenosine deaminase, Ada, is in mouse chromosome 2H3, and is not allelic with wasted, wst

The adenosine deaminase locus (Ada) in the mouse has been localized by in situ hybridization to band 2H3. Linkage analysis of backcross data has shown that Ada is 13.8 +/- 2.7 cM from the coat texture mutant, ragged, Ra. From the results of earlier work (Abbott, C. M., et al., Proc. Natl. Acad. Sci. USA 83:693, 1986), it had been suggested that wst was a low-activity allele of Ada, but this cannot be so because Ada and wst have been found to be nonallelic.

Parental influences on expression of glucose-6-phosphate dehydrogenase, G6pd, in the mouse; a case of imprinting

Glucose-6-phosphate dehydrogenase (G6PD) activity was measured in blood from heterozygotes for the normal allele G6pda and the low activity allele G6pda-mlNeu. In adult mice lower activity was found in G6pda/G6pda-mlNeu than in the reciprocal heterozygote G6pda-mlNeu/G6pda (the maternal allele being listed first). Thus, either the paternally derived allele was over-expressed or the maternally derived allele was under-expressed. By contrast, in younger mice the difference in G6PD activity in reciprocal crosses was less marked. The findings are interpreted in terms of differential imprinting of maternally and paternally inherited information. The explanation offered for age related differences is that, as a consequence of imprinting, either the paternal X-chromosome is preferentially reactivated, or cells in which the paternally derived allele is active are at a selective advantage, and proliferate better than those in which the maternally inherited allele is active.

Death of mouse embryos that lack a functional gene for glucose phosphate isomerase

A null allele of the Gpi-1s structural gene, that encodes glucose phosphate isomerase (GPI-1; E.C. 5.3.1.9), arose in a mutation experiment and was designated Gpi-1sa-m1H. The viability of homozygotes has been investigated. No offspring homozygous for the null allele were produced by intercrossing two heterozygotes, so the homozygous condition was presumed to be embryonic lethal. Embryos were produced by crossing Gpi-1sa/null heterozygous females and Gpi-1sb/null heterozygous males. Homozygous null embryos were identified at different stages of development by electrophoresis and staining either for GPI-1 alone or GPI-1 plus phosphoglycerate kinase (PGK) activity. At 6 1/2 and 7 1/2 days post coitum homozygous null embryos were present at approximately the expected 25% frequency (37/165; 22.4% overall) although at 7 1/2 days the homozygous null embryos tended to be small. By 8 1/2 days most homozygous null embryos were developmentally retarded and had not developed significantly further than at 7 1/2 days; some were dead or dying. By 9 1/2 days the homozygous null conceptus was characterised by a small implantation site that contained trophoblast and often a small amount of extraembryonic membrane. Surviving trophoblast tissue was also detectable at 10 1/2 days. Previous studies have shown that oocyte-coded GPI-1 persists only until 5 1/2 or 6 1/2 days. Survival of homozygous null embryos to 7 1/2 or 8 1/2 days and survival of certain extraembryonic tissue to 10 1/2 days suggests that the homozygous null condition may not be cell-lethal although it is certainly embryo-lethal. Mutant cells that are deficient in glycolysis may use the pentose phosphate shunt to bypass the block in glycolysis created by the deficiency of glucose phosphate isomerase, and/or might be rescued by the transport, from the maternal blood, of energy sources other than glucose (such as glutamine). Either strategy may only permit slow cell growth that would not be adequate to support normal embryogenesis. Transport of maternal nutrients would be more efficient to the trophoblast and extraembryonic membranes and this may help to explain why these tissues survive for longer than the embryo itself. The morphological similarity between homozygous nulls and androgenetic conceptuses, where the trophoblast also survives better than the embryo, is discussed.

Localization of Blvr, biliverdin reductase, on mouse chromosome 2

Biliverdin reductase, Blvr, has been mapped on mouse chromosome 2, using an electrophoretic variant. The gene order obtained from a five-point cross and calculating genetic distance as percentage recombination +/- SE was Blvr-3.7 +/- 1.8-pa-0.9 +/- 0.9-we-5.6 +/- 2.2-un-2.8 +/- 1.6-a. Thus, Blvr must be closely linked to several genes, limb deformity (ld), Strong's luxoid, (1st), and small eye (Sey), involved in limb and/or craniofacial development. In man, GCPS, Greig cephalopolysyndactyly syndrome, associated with limb anomalies and craniofacial dysmorphism has been assigned to 7p13. Thus GCPS probably maps near to BLVR, the human homolog of Blvr, and also to TCRG, T-cell receptor gamma. However, in mouse, Blvr and Tcrg are asyntenic, and the proposed murine homolog of GCPS is extra toes (Xt), closely linked to Tcrg on chromosome 13. Possibly in the common ancestor of man and mouse there was a cluster of genes for craniofacial and limb development, which remains linked to BLVR and TCRG in man, but has become broken up in the mouse with the loss of synteny of Blvr and Tcrg, although linkage of some genes in the cluster to Blvr and Tcrg has been retained.

The localization of G6pd, glucose-6-phosphate dehydrogenase, and mdx, muscular dystrophy in the mouse X chromosome

A low activity mutant of glucose-6-phosphate dehydrogenase,G6pda-m1Neuhas been used to positionG6pdin the mouseXchromosome. Linkage tests withtabby,Taandharlequin,Hq, indicate a likely gene order ofHq–G6pd–Ta. Muscular dystrophy,mdx, has been located by two-and three-point crosses usingHprt,Pgk-1andMobloand suggest a gene order ofHprt–mdx–Pgk-1–Moblo. Together with existing linkage data a tentative order for the seven loci isHq–Hprt–G6pd–mdx–Ta–Pgk-1–Moblo. The relative positions ofG6pdandmdxhave not been directly tested andG6pdis assigned provisionally proximal tomdx. In the three point test usingHq,G6pdandTathe recombination frequency found betweenHqandTawas 9·9 ± 2·6%, substantially less than the value of 20·5 ± 2·1% reported by Isaacsonet al.(1974).

An allele at the triose phosphate isomerase, Tpi-1 locus on chromosome 6 recovered from feral mice

An animal with low erythrocyte triose phosphate isomerase (TPI) activity was found amongst mice trapped on a farm in Leicestershire. The low TPI activity was caused by the segregation of a single co-dominant gene which also affected theKmfor glyceraldehyde-3-phosphate and heat stability of the enzyme. We designate the geneTpi-1, the structural locus for TPI, with theaallele in the common inbred strains and theballele derived from the wild-caught mouse.Tpi-1was known to be on chromosome 6 by somatic cell techniques and, as shown in a preliminary report (Peters & Bulfield, 1984), we have confirmed and extended this finding using three chromosome-6 marker genes giving the order:Sig-28-Lc-11-Miwh-16-Tpi-1.