Skeletal defects in paternal uniparental disomy for chromosome 14 are re-capitulated in the mouse model (paternal uniparental disomy 12)

Temple syndrome and Kagami-Ogata syndrome: clinical presentations, genotypes, models and mechanisms

Temple syndrome (TS) and Kagami-Ogata syndrome (KOS) are imprinting disorders caused by absence or overexpression of genes within a single imprinted cluster on human chromosome 14q32. TS most frequently arises from maternal UPD14 or epimutations/deletions on the paternal chromosome, whereas KOS most frequently arises from paternal UPD14 or epimutations/deletions on the maternal chromosome. In this review, we describe the clinical symptoms and genetic/epigenetic features of this imprinted region. The locus encompasses paternally expressed protein-coding genes (DLK1, RTL1 and DIO3) and maternally expressed lncRNAs (MEG3/GTL2, RTL1as and MEG8), as well as numerous miRNAs and snoRNAs. Control of expression is complex, with three differentially methylated regions regulating germline, placental and tissue-specific transcription. The strong conserved synteny between mouse chromosome 12aF1 and human chromosome 14q32 has enabled the use of mouse models to elucidate imprinting mechanisms and decipher the contribution of genes to the symptoms of TS and KOS. In this review, we describe relevant mouse models and highlight their value to better inform treatment options for long-term management of TS and KOS patients.

The Genetic Etiology Diagnosis of Fetal Growth Restriction Using Single-Nucleotide Polymorphism-Based Chromosomal Microarray Analysis

Background: An increase in pathogenic copy number variants (pCNVs) has been recognized to associate with fetal growth restriction (FGR). Here, we aim to explore the application value of chromosomal microarray analysis (CMA) in prenatal diagnosis of FGR. Methods: Prenatal ultrasound was applied to identify FGR. A total of 149 pregnant women with FGR were enrolled in our study. All subjects underwent karyotype analysis and CMA to reveal the chromosomal abnormalities. Results: In this study, all subjects were successfully detected by karyotype and CMA analyses. Of these subjects, the chromosomal abnormalities detection rate was 5.37% (8/149) for karyotyping and 13.42% (20/149) for CMA, respectively. Among them, an 8.05% (12/149) incremental yield of CMA over karyotype analysis was observed (p = 0.004). In addition, a significant difference of pCNV detection rate was observed between the groups with different high-risk factors (p = 0.005). The FGR with structural anomalies group showed the highest pCNV detection rate (33.33%), followed by the FGR with non-structural anomalies group (8.77%) and the isolated FGR group (8.06%). Conclusion: In conclusion, CMA technology showed an effective application value in etiology diagnosis of FGR. We believe that CMA should be recommended as first-line detection technology for prenatal diagnosis in FGR.

Expression of miRNAs from the Imprinted DLK1/DIO3 Locus Signals the Osteogenic Potential of Human Pluripotent Stem Cells

Substantial variations in differentiation properties have been reported among human pluripotent cell lines (hPSC), which could affect their utility and clinical safety. We characterized the variable osteogenic capacity observed between different human pluripotent stem cell lines. By focusing on the miRNA expression profile, we demonstrated that the osteogenic differentiation propensity of human pluripotent stem cell lines could be associated with the methylation status and the expression of miRNAs from the imprinted DLK1/DIO3 locus. More specifically, quantitative analysis of the expression of six different miRNAs of that locus prospectively identified human embryonic stem cells and human-induced pluripotent stem cells with differential osteogenic differentiation capacities. At the molecular and functional levels, we showed that these miRNAs modulated the expression of the activin receptor type 2B and the downstream signal transduction, which impacted osteogenesis. In conclusion, miRNAs of the imprinted DLK1/DIO3 locus appear to have both a predictive value and a functional impact in determining the osteogenic fate of human pluripotent stem cells.

Interchromosomal template-switching as a novel molecular mechanism for imprinting perturbations associated with Temple syndrome

Background

Intrachromosomal triplications (TRP) can contribute to disease etiology via gene dosage effects, gene disruption, position effects, or fusion gene formation. Recently, post-zygotic de novo triplications adjacent to copy-number neutral genomic intervals with runs of homozygosity (ROH) have been shown to result in uniparental isodisomy (UPD). The genomic structure of these complex genomic rearrangements (CGRs) shows a consistent pattern of an inverted triplication flanked by duplications (DUP-TRP/INV-DUP) formed by an iterative DNA replisome template-switching mechanism during replicative repair of a single-ended, double-stranded DNA (seDNA), the ROH results from an interhomolog or nonsister chromatid template switch. It has been postulated that these CGRs may lead to genetic abnormalities in carriers due to dosage-sensitive genes mapping within the copy-number variant regions, homozygosity for alleles at a locus causing an autosomal recessive (AR) disease trait within the ROH region, or imprinting-associated diseases.

Methods

Here, we report a family wherein the affected subject carries a de novo 2.2-Mb TRP followed by 42.2 Mb of ROH and manifests clinical features overlapping with those observed in association with chromosome 14 maternal UPD (UPD(14)mat). UPD(14)mat can cause clinical phenotypic features enabling a diagnosis of Temple syndrome. This CGR was then molecularly characterized by high-density custom aCGH, genome-wide single-nucleotide polymorphism (SNP) and methylation arrays, exome sequencing (ES), and the Oxford Nanopore long-read sequencing technology.

Results

We confirmed the postulated DUP-TRP/INV-DUP structure by multiple orthogonal genomic technologies in the proband. The methylation status of known differentially methylated regions (DMRs) on chromosome 14 revealed that the subject shows the typical methylation pattern of UPD(14)mat. Consistent with these molecular findings, the clinical features overlap with those observed in Temple syndrome, including speech delay.

Conclusions

These data provide experimental evidence that, in humans, triplication can lead to segmental UPD and imprinting disease. Importantly, genotype/phenotype analyses further reveal how a post-zygotically generated complex structural variant, resulting from a replication-based mutational mechanism, contributes to expanding the clinical phenotype of known genetic syndromes. Mechanistically, such events can distort transmission genetics resulting in homozygosity at a locus for which only one parent is a carrier as well as cause imprinting diseases.

Electronic supplementary material

The online version of this article (10.1186/s13073-019-0633-y) contains supplementary material, which is available to authorized users.

Aberrant expression of MICO1 and MICO1OS in deceased somatic cell nuclear transfer calves

Incomplete reprogramming of a donor nucleus following somatic cell nuclear transfer (SCNT) results in aberrant expression of developmentally important genes, and is the primary source of the phenotypic abnormalities observed in cloned animals. Expression of non-coding RNAs in the murine Dlk1-Dio3 imprinted domain was previously shown to correlate with the pluripotency of mouse induced pluripotent stem cells. In this study, we examined the transcription of the bovine orthologs from this locus, MICO1 (Maternal intergenic circadian oscillating 1) and MICO1OS (MICO1 opposite strand), in tissues from artificially inseminated and SCNT calves that died during the perinatal period. A single-nucleotide polymorphism (SNP), a T-to-C transition, was used to analyze the allelic transcription of MICO1. Our results indicate monoallelic expression of the MICO1C allele among the six analyzed tissues (heart, liver, spleen, lung, kidney, and brain) of artificially inseminated calves, indicating that this gene locus may be imprinted in bovine. Conversely, we observed variable allelic transcription of MICO1 in SCNT calves. We asked if DNA methylation regulated the monoallelic expression of MICO1 and MICO1OS by evaluating the methylation levels of six regions within or around this locus in tissues with normal or aberrant MICO1 transcription; all of the samples from either artificially inseminated or SCNT calves exhibited hypermethylation, implying that DNA methylation may not be involved in regulating its monoallelic expression. Furthermore, three imprinted genes (GTL2, MEG9, and DIO3) nearby MICO1 showed monoallelic expression in SCNT calves with aberrant MICO1 transcription, indicating that not all of the genes in the bovine DLK1-DIO3 domain are mis-regulated.

In Pursuit of New Imprinting Syndromes by Epimutation Screening in Idiopathic Neurodevelopmental Disorder Patients

Alterations of epigenetic mechanisms, and more specifically imprinting modifications, could be responsible of neurodevelopmental disorders such as intellectual disability (ID) or autism together with other associated clinical features in many cases. Currently only eight imprinting syndromes are defined in spite of the fact that more than 200 genes are known or predicted to be imprinted. Recent publications point out that some epimutations which cause imprinting disorders may affect simultaneously different imprinted loci, suggesting that DNA-methylation may have been altered more globally. Therefore, we hypothesised that the detection of altered methylation patterns in known imprinting loci will indirectly allow identifying new syndromes due to epimutations among patients with unexplained ID. In a screening for imprinting alterations in 412 patients with syndromic ID/autism we found five patients with altered methylation in the four genes studied: MEG3, H19, KCNQ1OT1, and SNRPN. Remarkably, the cases with partial loss of methylation in KCNQ1OT1 and SNRPN present clinical features different to those associated with the corresponding imprinting syndromes, suggesting a multilocus methylation defect in accordance with our initial hypothesis. Consequently, our results are a proof of concept that the identification of epimutations in known loci in patients with clinical features different from those associated with known syndromes will eventually lead to the definition of new imprinting disorders.

MicroRNAs of the miR379-410 cluster: New players in embryonic neurogenesis and regulators of neuronal function

The imprinted miR379–410 cluster contains 38 microRNAs (miRNAs) that are involved in diverse neurodevelopmental processes and are important regulators of neuronal function. The implications of these miRNAs in neurological diseases have been recently recognized.In the present minireview, the current findings regarding the brain-specific functions of miR379–410 cluster miRNAs are summarized and discussed.

Loss of non-coding RNA expression from the DLK1-DIO3 imprinted locus correlates with reduced neural differentiation potential in human embryonic stem cell lines

INTRODUCTION

Pluripotent stem cells are increasingly used to build therapeutic models, including the transplantation of neural progenitors derived from human embryonic stem cells (hESCs). Recently, long non-coding RNAs (lncRNAs), including delta-like homolog 1 gene and the type III iodothyronine deiodinase gene (DLK1-DIO3) imprinted locus-derived maternally expressed gene 3 (MEG3), were found to be expressed during neural development. The deregulation of these lncRNAs is associated with various neurological diseases. The imprinted locus DLK1-DIO3 encodes abundant non-coding RNAs (ncRNAs) that are regulated by differential methylation of the locus. We aim to study the correlation between the DLK1-DIO3-derived ncRNAs and the capacity of hESCs to differentiate into neural lineages.

METHODS

We classified hESC sublines into MEG3-ON and MEG3-OFF based on the expression levels of MEG3 and its downstream microRNAs as detected by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). A cDNA microarray was used to analyze the gene expression profiles of hESCs. To investigate the capacity of neural differentiation in MEG3-ON and MEG3-OFF hESCs, we performed neural lineage differentiation followed by neural lineage marker expression and neurite formation analyses via qRT-PCR and immunocytochemistry, respectively. MEG3-knockdown via small interfering RNA (siRNA) and small hairpin RNA (shRNA) was used to investigate the potential causative effect of MEG3 in regulating neural lineage-related gene expression.

RESULTS

DLK1-DIO3-derived ncRNAs were repressed in MEG3-OFF hESCs compared with those in the MEG3-ON hESCs. The transcriptome profile indicated that many genes related to nervous system development and neural-type tumors were differentially expressed in MEG3-OFF hESCs. Three independent MEG3-knockdown assays using different siRNA and shRNA constructs consistently resulted in downregulation of some neural lineage genes. Lower expression levels of stage-specific neural lineage markers and reduced neurite formation were observed in neural lineage-like cells derived from MEG3-OFF-associated hESCs compared with those in the MEG3-ON groups at the same time points after differentiation.

CONCLUSIONS

Repression of ncRNAs derived from the DLK1-DIO3 imprinted locus is associated with reduced neural lineage differentiation potential in hESCs.

Genomic imprinting of the type 3 thyroid hormone deiodinase gene: regulation and developmental implications

BACKGROUND

In recent years, findings in a number of animal and human models have ignited renewed interest in the type 3 deiodinase (D3), the main enzyme responsible for the inactivation of thyroid hormones. The induction of D3 in models of illness and injury has raised critical questions about the physiological significance of reduced thyroid hormone availability in those states. Phenotypes in transgenic mice lacking this enzyme also point to important developmental roles for D3. A critical determinant of D3 expression is genomic imprinting, an epigenetic phenomenon that regulates a small number of dosage-critical genes in the mammalian genome. The D3 gene (Dio3) is imprinted and preferentially expressed from one of the alleles in most tissues.

SCOPE OF REVIEW

In the context of the physiological significance of D3 and the characteristics and purported origins of genomic imprinting, we review the current knowledge about the epigenetic mechanisms specifying gene dosage in the Dio3 locus.

MAJOR CONCLUSIONS

Altered Dio3 dosage is detrimental to development, suggesting that the level of thyroid hormone action needs to be exquisitely tailored in a timely fashion to the requirements of particular tissues. An appropriate Dio3 dosage is the result of the coordinated action of certain genomic elements and epigenetic marks in the Dlk1-Dio3 domain.

GENERAL SIGNIFICANCE

The imprinting of Dio3 prompts intriguing questions about why the level of thyroid hormone signaling should be regulated in this rare epigenetic manner, and to what extent altered Dio3 expression due to aberrant imprinting may be implicated in human conditions. This article is part of a Special Issue entitled Thyroid hormone signalling.

Spatiotemporal expression pattern of Mirg, an imprinted non-coding gene, during mouse embryogenesis

Recent research has revealed that the maternal non-coding RNA genes (Gtl2, Rian and Mirg) from the Dlk1-Dio3 imprinted cluster are closely related to the full development potential of the induced pluripotent stem cells (iPSCs). Transcriptional silencing of these genes failed to generate all-iPSC mice, indicating their significant contribution to embryogenesis. However, except for Gtl2, little information regarding these genes has been acquired in this cluster. In the present study, we analyzed the spatiotemporal expression patterns of Mirg during mouse embryogenesis. Using in situ hybridization and quantitative PCR, we demonstrated that Mirg non-coding RNA exhibited sustained expression throughout mouse embryogenesis from E8.5 to E18.5. Strong expression was detected in the central nervous system (E9.5-E15.5) and various skeletal muscles (E13.5 and E15.5), and the subcellular localization appeared to be in the nuclei. The pituitary and adrenal gland also showed high expression of Mirg, but, unlike the skeletal muscles and the neural circuitry, the signals were not concentrated in the nuclei. In the major internal organs, Mirg maintained low expression during embryogenesis (E12.5-E18.5) whereas in the liver and the developing lung, Mirg was expressed with a gradually decreasing trend and a gradually raising trend, respectively. These findings indicate that temporal regulation of Mirg expression may be required during specific stages and in specific tissues during embryonic development.

Radiological evaluation of dysmorphic thorax of paternal uniparental disomy 14

BACKGROUND

The "coat-hanger" sign of the ribs with a bell-shaped thorax has been known as a radiological hallmark of the paternal uniparental disomy 14 (upd(14)pat).

OBJECTIVE

To quantitatively determine the differences in thoracic deformity between upd(14)pat and other bone diseases with thoracic hypoplasia and to establish the age-dependent evolution.

MATERIALS AND METHODS

The subjects comprised 11 children with upd(14)pat. The angle between the 6th posterior rib and the horizontal axis was measured (coat hanger angle; CHA). The ratio of the mid- to widest thorax diameter (M/W ratio) was calculated for the bell-shaped thorax.

RESULTS

CHA ranged from +28.5 to 45° (mean; 35.1° ± 5.2) in upd(14)pat, and from -19.8 to 21° (-3.3 ± 13°) in bone dysplasias (p < 0.01). The M/W ratio ranged from 58% to 93% (75.4 ± 10) in upd(14)pat, and from 80% to 92% (86.8 ± 3.3) in bone dysplasias (p < 0.05). Serial radiographs revealed that CHA remained constant during early childhood, while the M/W ratio gradually increased with age.

CONCLUSION

The "coat-hanger" sign of upd(14)pat provides a distinctive radiological gestalt that makes it possible to differentiate the disorder from other skeletal dysplasias. By contrast, the bell-shaped thorax is significant only in the neonatal period.

Segmental paternal uniparental disomy (patUPD) of 14q32 with abnormal methylation elicits the characteristic features of complete patUPD14

Uniparental disomy (UPD) for chromosome 14 is associated with well-recognized phenotypes, depending on the parent of origin. Studies in mouse models and human patients have implicated the involvement of the distal region of the long arm of chromosome 14 in the distinctive phenotypes. This involvement is supported by the identification of an imprinting cluster at chromosome 14q32, encompassing the differentially methylated regions (DMRs), IG-DMR and MEG3-DMR, as well as the maternally expressed genes GTL2, DIO3, and RTL1 and the paternally expressed genes DLK1, RTL1as, and MEG8. Here we report on a preterm female infant with distal segmental paternal UPD14 (upd(14)pat) of 14q32-14q32.33, which resulted in thoracic deformity secondary to rib abnormalities ("coat-hanger" rib sign), polyhydramnios, and other congenital abnormalities characteristically described in cases of complete upd(14)pat. Microsatellite investigation demonstrated UPD of markers D14S250 and D14S1010, encompassing a approximately 3.5 Mb region of distal 14q and involving the imprinting cluster. This case provided insight into the etiology of the phenotypic effects of upd(14)pat, prompting methylation analysis of the GTL2 promoter and the DMR between GTL2 and DLK1. We compare the physical findings seen in this case with those of patients with other causes of abnormal methylation of 14q32, which consistently result in certain distinct clinical features, regardless of the cytogenetic and molecular etiology.

Guidelines for the prenatal diagnosis of fetal skeletal dysplasias

The osteochondrodysplasias, or skeletal dysplasias are a genetically heterogeneous group of over 350 distinct disorders, and many of them can present in the prenatal period as demonstrated by ultrasound. Differentiating these disorders in the prenatal period can be challenging because they are rare and many of the ultrasound findings are not necessarily pathognomic for a specific disorder. However, differentiating known lethal disorders from nonlethal disorders, providing differential diagnoses before delivery, determining postdelivery management plans and ultimately determining accurate recurrences risks to the at-risk couples improves patient care. These guidelines provide an approach to a fetus suspected of manifesting a skeletal dysplasia.

Genomic imprinting at the mammalian Dlk1-Dio3 domain

Genomic imprinting causes genes to be expressed or repressed depending on their parental origin. The majority of imprinted genes identified to date map in clusters and much of our knowledge of the mechanisms, function and evolution of imprinting have emerged from their analysis. The cluster of imprinted genes delineated by the delta-like homolog 1 gene and the type III iodothyronine deiodinase gene (Dlk1-Dio3) is located on distal mouse chromosome 12 and human chromosome 14. Its developmental importance is exemplified by severe phenotypes associated with altered dosage of these genes in mice and humans. The domain contains three imprinted protein-coding genes, Dlk1, Rtl1 and Dio3, expressed from the paternally inherited chromosome and several imprinted large and small noncoding RNA genes expressed from the maternally inherited homolog. Here, we discuss the function and regulation of imprinting at this domain.

Evaluation of prenatal-onset osteochondrodysplasias by ultrasonography: a retrospective and prospective analysis

The osteochondrodysplasias or skeletal dysplasias are a heterogenous group of over 350 distinct disorders of skeletogenesis. Many manifest in the prenatal period, making them amenable to ultrasound prenatal diagnosis. A retrospective analysis evaluated 1,500 cases referred to the International Skeletal Dysplasia Registry (ISDR) to determine the relative frequency of specific osteochondrodysplasias and correlation of ultrasound versus radiographic diagnoses for these disorders. Within the retrospective cohort of 1,500 cases, 85% of the referred cases represented well-defined skeletal dysplasias, and the other 15% of cases were a mixture of genetic syndromes and probable early-onset intrauterine growth restriction. The three most common prenatal-onset skeletal dysplasias were osteogenesis imperfecta type 2, thanatophoric dysplasia and achondrogenesis 2, accounting for almost 40% of the cases. In a prospective analysis of 500 cases using a standardized ultrasound approach to the evaluation of these disorders, the relative frequencies of osteogenesis imperfecta type 2, thanatophoric dysplasia and achondrogenesis 2 were similar to the retrospective analysis. This study details the relative frequencies of specific prenatal-onset osteochondrodysplasias, their heterogeneity of prenatal-onset skeletal disorders and provides a standardized prenatal ultrasound approach to these disorders which should aid in the prenatal diagnosis of fetuses suspected of manifesting skeletal dysplasias.

DNA methylation imprints on the IG-DMR of the Dlk1-Gtl2 domain in mouse male germline

Mouse genomes show a large cluster of imprinted genes at the Dlk1-Gtl2 domain in the distal region of chromosome 12. An intergenic-differentially methylated region (IG-DMR) located between Dlk1 and Gtl2 is specifically methylated in the male germline; IG-DMR regulates the parental allele-specific expression of imprinted genes. Here, we show the resetting of IG-DMR methylation marks during male germ-cell differentiation. For parental allele-specific methylation analysis, polymorphisms were detected in a 2.6-kb IG-DMR in three mouse strains. Bisulfite methylation analysis showed erasure of the marks by E14 and re-establishment before birth. The IG-DMR methylation status was maintained in spermatogonia and spermatocytes of mature testes. The IG-DMR methylation status established before birth is thus maintained throughout the lifetime in the male germline.

Paternal uniparental isodisomy for chromosome 14 with mosaicism for a supernumerary marker chromosome 14

Uniparental disomy (UPD) describes the inheritance of two homologous chromosomes from a single parent. Disease phenotypes associated with UPD and chromosomal imprinting, rather than with mutations, include Beckwith-Wiedemann syndrome (paternal UPD11p), Angelman syndrome (paternal UPD15), Prader-Willi syndrome (maternal UPD15), and transient neonatal diabetes (paternal UPD6). Here we report on the first case of paternal uniparental isodisomy of chromosome 14 with a mosaicism for a supernumerary marker chromosome 14. The patient demonstrated a small thorax with a 'coat hanger' shape of the ribs, kyphoscoliosis, hypoplasia of the maxilla and mandible, a broad nasal bridge with anteverted nares, contractures of the wrists with ulnar deviation bilaterally, diastasis recti, and marked muscle hypotonia. Vertical skin creases under the chin and stippled epiphyses of the humeri were features not previously described in patients with paternal UPD14. This case illustrates that as with the finding of an isochromosome, a supernumerary marker chromosome can be an important clue to the presence of UPD14.

Differential regulation of imprinting in the murine embryo and placenta by the Dlk1-Dio3 imprinting control region

Genomic imprinting is an epigenetic mechanism controlling parental-origin-specific gene expression. Perturbing the parental origin of the distal portion of mouse chromosome 12 causes alterations in the dosage of imprinted genes resulting in embryonic lethality and developmental abnormalities of both embryo and placenta. A 1 Mb imprinted domain identified on distal chromosome 12 contains three paternally expressed protein-coding genes and multiple non-coding RNA genes, including snoRNAs and microRNAs, expressed from the maternally inherited chromosome. An intergenic, parental-origin-specific differentially methylated region, the IG-DMR, which is unmethylated on the maternally inherited chromosome, is necessary for the repression of the paternally expressed protein-coding genes and for activation of the maternally expressed non-coding RNAs: its absence causes the maternal chromosome to behave like the paternally inherited one. Here, we characterise the developmental consequences of this epigenotype switch and compare these with phenotypes associated with paternal uniparental disomy of mouse chromosome 12. The results show that the embryonic defects described for uniparental disomy embryos can be attributed to this one cluster of imprinted genes on distal chromosome 12 and that these defects alone, and not the mutant placenta, can cause prenatal lethality. In the placenta, the absence of the IG-DMR has no phenotypic consequence. Loss of repression of the protein-coding genes occurs but the non-coding RNAs are not repressed on the maternally inherited chromosome. This indicates that the mechanism of action of the IG-DMR is different in the embryo and the placenta and suggests that the epigenetic control of imprinting differs in these two lineages.

Analysis of mouse conceptuses with uniparental duplication/deficiency for distal chromosome 12: comparison with chromosome 12 uniparental disomy and implications for genomic imprinting

Distal mouse chromosome 12 is imprinted. Phenotypic analysis of mouse embryos with maternal or paternal uniparental disomy for the whole of chromosome 12 has characterized the developmental defects associated with the altered dosage of imprinted genes on this chromosome. Here we conduct a characterization of maternal and paternal Dp(dist12) mice using the reciprocal translocation T(4;12)47H. This limits the region analysed to the chromosomal domain distal to the T47H breakpoint in B3 on mouse chromosome 12. Both MatDp(dist12)T47H and PatDp(dist12)T47H conceptuses are non-viable and the frequency of recovery of Dp(dist12) conceptuses by 10.5 days post coitum (dpc) was lower than expected after normal adjacent-1 disjunction. A subset of MatDp(dist12) embryos can survive up to one day post partum. In contrast to paternal uniparental disomy 12 embryos, no live PatDp (dist12) embryos were recovered after 16.5 days of gestation. Other phenotypes observed in maternal and paternal chromosome 12 uniparental disomy mice are recapitulated in the Dp(dist12) mice and include placental, muscle and skeletal defects. Additional defects were also noted in the skin of both MatDp(dist12) and maternal uniparental disomy 12 embryos. This study shows that the developmental abnormalities associated with the altered parent of origin for mouse chromosome 12 can be attributed to the genomic region distal to the T47H breakpoint.

Imprinted genes and their role in human fetal growth

Growth is defined as the progressive increase in size and is listed as one of the eight main characteristics of life. In human gestation the most rapid growth phase is from 16 to 32 weeks when first there is both cell number and size increase and then from 32 weeks onwards there is continued size increase (Pollack and Divon, 1992). The mechanism of growth in utero is of fundamental interest to clinicians and scientists because of its implications for neonatal health. Growth is multifactorial in origin with both genetics and environment contributing equally large parts. Despite this complexity analysis of the candidate genes involved is possible using simple tissue biopsies at the relevant stages of development. Of particular interest in understanding fetal growth is the analysis of a group of genes that show a parent-of-origin effect known as genomic imprinting. Imprinted genes are not only found in eutherian (placental) and metatherian (marsupial) mammals but surprisingly also in plants. Nevertheless, their evolution in mammals appears to be linked primarily to placentation. It is thought to result from a potential conflict between the parents in terms of the drive to successfully propagate their own separate genes and the mother's added drive for her survival through the pregnancy to reproduce again. This means that the mother wants to restrict fetal growth and the father to enhance it.

Comparative phylogenetic analysis reveals multiple non-imprinted isoforms of opossum Dlk1

Imprinted genes are monoallelically expressed in a parent-of-origin manner and were previously identified in both marsupials and eutherians, but not in monotremes. Phylogenetic comparison of imprinted domains is a powerful tool for investigating the molecular and adaptive evolution of this unique gene regulatory mechanism. Herein, we report that multiple transcripts of Dlk1 (Delta, Drosophila, Homolog-like 1) are expressed in the opossum, but none are imprinted. Thus, we provide the first example of a reciprocally imprinted gene domain in which imprinting evolved in a common ancestor to eutherian rather than therian mammals. Moreover, the reciprocally imprinted Meg3 (Maternally Expressed Gene 3), found downstream of Dlk1 in eutherian mammals, is absent in the opossum. We propose that the Meg3 sequence integrated into the eutherian Dlk1 domain via a LINE-1 element and that Dlk1 became imprinted in eutherian mammals only after this downstream integration. These findings clearly demonstrate that imprinted genes did not all evolve before the divergence of marsupials and eutherians.

Segmental and full paternal isodisomy for chromosome 14 in three patients: Narrowing the critical region and implication for the clinical features

We report on segmental and full paternal isodisomy for chromosome 14 in three previously unreported Japanese patients. Patient 1 was a 5(6/12)-year-old girl, Patient 2 was a male neonate, and Patient 3 was a -year-old girl. Physical examination at birth showed various somatic features characteristic of paternal uniparental disomy for chromosome 14 (upd(14)pat) such as hairy forehead, protruding philtrum, micrognathia, small thorax, and abdominal wall defects in Patients 1-3, and the constellation of somatic features was persistently observed in Patients 1 and 3. Radiological studies at birth delineated unique bell-shaped thorax with coat-hanger appearance of the ribs in Patients 1-3, but the thoracic deformity ameliorated in Patients 1 and 3 by mid childhood. Chromosome analysis showed a 46,XX karyotype in Patients 1 and 3 and was not performed in Patient 2. Microsatellite analysis indicated full paternal isodisomy for chromosome 14 in Patients 1 and 2 and segmental paternal isodisomy for chromosome 14 distal to D14S981 at 14q23.3 in Patient 3. Methylation specific PCR assay for the differentially methylated region (DMR) of GTL2 at 14q32 yielded positive products with methylated allele specific primers and no products with unmethylated allele specific primers in Patients 1-3. Since clinical phenotype was similar between Patient 3 with segmental upd(14)pat and Patients 1 and 2 with full upd(14)pat, the results are keeping with the 14q32 localized imprinted genes as the critical components of the phenotype observed in upd(14)pat and help narrow the search for additional genes to the approximately 40 Mb region distal to D14S981. Furthermore, it is likely that the characteristic thoracic deformity ameliorates with age.

Paternal uniparental disomy of chromosome 14: confirmation of a clinically-recognizable phenotype

We report on a girl with a dicentric chromosome 14 [45,XX,inv(9)(p11q13),dic(14;14)(p11.1;p11.1)] with paternal uniparental disomy (UPD) for chromosome 14. Clinical findings include severe hypotonia, thoracic dystrophy, diastasis recti, swallowing difficulties with aspiration, developmental delay, and multiple minor anomalies. UPD for chromosome 14 has been documented with paternal UPD much less commonly than with maternal UPD. There have been ten cases of paternal UPD for chromosome 14 and one case of segmental paternal isodisomy of chromosome 14. Many of the findings are nonspecific, but the radiographic rib findings (referred to as the "coat-hanger" sign) are characteristic for this condition. UPD 14 studies should be performed in children thought to have Jeune asphyxiating thoracic dystrophy or other related osteochondrodysplasias when the diagnosis is in question. Our patient and the previously reported cases support a discrete recognizable phenotype for paternal UPD for chromosome 14.