Mechanics of vaginal breech birth: Factors influencing obstetric maneuver rate, duration of active second stage of labor, and neonatal outcome

BACKGROUND

We investigated possible parameters that could predict the need for obstetric maneuvers, the duration of the active second stage of labor (i.e., the duration of active pushing), and short-term neonatal outcome in vaginal breech births.

MATERIALS AND METHODS

We performed a retrospective analysis of 268 successful singleton vaginal breech births in women without previous vaginal births from January 2015 to August 2022. Multivariable regression was used to investigate associations between maternal and fetal characteristics (including antepartum magnetic resonance (MR) pelvimetry) with obstetric maneuvers, the duration of active second stage of labor, pH values, and admission to the neonatal unit. Models for the prediction of obstetric maneuvers were built and internally validated.

RESULTS

Obstetric maneuvers were performed in a total of 130 women (48.5%). A total of 32 neonates (11.9%) had to be admitted to the neonatal unit. The intertuberous distance (ITD) (p < 0.001), epidural analgesia (p < 0.001), and birthweight (p = 0.026) were associated with the duration of active second stage of labor. ITD (p = 0.028) and birthweight (p = 0.011) were also independently associated with admission to the neonatal unit, while pH values below 7.10 dropped significantly (p = 0.0034) if ITD was ≥13 cm. Furthermore, ITD (p < 0.001) and biparietal diameter (p = 0.002) were independent predictors for obstetric maneuvers.

CONCLUSIONS

ITD is independently associated with the duration of active second stage of labor. Thus, it can predict suboptimal birth mechanics in the last stage of birth, which may lead to the need for obstetric maneuvers, lower arterial pH values, and admission to the neonatal unit. Consequently, MR pelvimetry gives additional information for practitioners and birthing people preferring a vaginal breech birth.

Novel Three-Dimensional Body Scan Anthropometry versus MR-Pelvimetry for Vaginal Breech Delivery Assessment

In this prospective, monocentric study, we investigated the potency of a novel three-dimensional (3D) body scanner for external pelvic assessment in birth planning for intended vaginal breech delivery. Between April 2021 and June 2022, 73 singleton pregnancies with intended vaginal birth from breech presentation (>36.0 weeks of gestation) were measured using a pelvimeter by Martin, a three-dimensional body scanner, and MR-pelvimetry. Measures were related to vaginal birth and intrapartum cesarean section. A total of 26 outer pelvic dimensions and 7 inner pelvic measurements were determined. The rate of successful vaginal breech delivery was 56.9%. The AUC (area under the curve) of the obstetric conjugate (OC) measured by MRI for predicting the primary outcome was 0.62 (OR 0.63; p = 0.22), adjusted for neonatal birth weight 0.66 (OR 0.60; p = 0.19). Of the 22 measured 3D body scanner values, the ratio of waist girth to maternal height showed the best prediction (AUC = 0.71; OR 1.27; p = 0.015). The best predictive pelvimeter value was the distantia spinarum with an AUC of 0.65 (OR = 0.80). The 3D body scanner technique is at least equal to predict successful vaginal breech delivery compared to MRI diagnostics. Further large-scale, prospective studies are needed to verify these results.

Angiography derived index of microvascular resistance (IMR) in Takotsubo syndrome

Background and purpose

Coronary microvascular dysfunction (CMD) has been proposed as a key driver in the etiopathogenesis of Takotsubo syndrome (TTS), likely related to an “adrenergic storm” upon a susceptible microvascular circulation. The aim of our manuscript was to assess and quantify CMD in patients with TTS through angiography-derived index of microcirculation (IMR) and evaluate its correlation with clinical presentation.

Methods

Coronary angiograms of 41 consecutive TTS patients were retrospectively offline analyzed to derive angiography-based indices of CMD. Three recently developed indices (NH-IMRangio, AngioIMR and A-IMR) were calculated and compared based on Quantitative Flow Reserve (QFR) analysis. CMD was defined as an IMRangio ≥25 units. The correlation between CMD and clinical presentation and outcomes was then assessed.

Results

Median age was 76 years, 85.7% were women and mean left ventricular ejection fraction (LVEF) at first echocardiogram was 41.2%. Angiography-derived IMR was higher in Left Anterior Descending artery (LAD) than Circumflex artery (LCX) and Right Coronary artery (RCA) with either NH-IMRangio (52.7 vs 35.3 vs 41.4), AngioIMR (47.2 vs 31.8 vs 37.3) or A-IMR (52.7 vs 36.1 vs 41.8). All patients presented CMD with angiography-derived IMR ≥25 in at least one territory with each formula. Angiography-derived IMR in LAD territory was significantly higher in patients presenting with LVEF impairment (≤40%) than in those with preserved ventricular global function (NH-IMRangio: 59.3 vs 46.3, p. value=0.030; AngioIMR: 52.9 vs 41.4, p-value=0.037; A-IMR: 59.2 vs 46.3, p-value=0.035).

Conclusion

CMD, assessed with angiography-derived IMR, is a common finding in TTS and it is inversely correlated with LV function. The available formulas have a substantial superimposable diagnostic performance in assessing coronary microvascular function.

Funding Acknowledgement

Type of funding sources: None.

P73 ANGIOGRAPHY–DERIVED INDEX OF MICROVASCULAR RESISTANCE (IMR–ANGIO) IN TAKOTSUBO SYNDROME

Introduction

Coronary microvascular dysfunction (CMD) has been proposed as a key driver in the etiopathogenesis of Takotsubo syndrome (TTS), likely related to an “adrenergic storm” upon a susceptible microvascular circulation. The aim of our manuscript was to assess and quantify CMD in patients with TTS through non–invasive angio–derived index of microcirculation (IMRangio) and evaluate its correlation with clinical and instrumental presentation.

Methods

41 consecutive TTS patients were retrospectively analyzed. Three different formulas for compute Non–Hyperemic IMRangio (NH–IMRangio) derived by 3D–Quantitative Coronary Angiography (3D–QCA) and Quantitative Flow Reserve (QFR) analysis were used according to each fluidodynamic mathematical expression as reported by respective authors. CMD was defined as an IMRangio ≥ 25. The correlation between NH–IMRangio and clinical presentation and the comparation between the three formulas were provided.

Results

Median age was 76 years, 85.7% were women and mean left ventricular ejection fraction (LVEF) at first echocardiogram was 41.2%. NH–IMRangio was higher in Left Anterior Descending artery (LAD) than Circumflex artery (CX) and Right Coronary artery (RCA) with either NH–IMRangio 1 (52.7 vs 35.3 vs 41.4), NH–IMRangio 2 (47.2 vs 31.8 vs 37.3) or NH–IMRangio 3 (52.7 vs 36.1 vs 41.8). All patients presented CMD with NH–IMR angio ≥ 25 in at least one territory with each formula. NH–IMRangio in LAD territory was significantly higher in patients presenting with LVEF impairment (≤40%) than in those with preserved ventricular global function (NH–IMRangio LAD 1: 59.3 vs 46.3, p. value=0.030; NH–IMRangio LAD 2: 52.9 vs 41.4, p–value=0.037; NH–IMRangio LAD 3: 59.2 vs 46.3, p–value=0–035). Association between NH–IMRangio computed in LAD and LVEF showed a moderate correlation (NH–IMRangio 1: r = –0,3485, Rho = 0,1214, p = 0,0256; NH–IMRangio 2: r = –0,3513; Rho = 0,1234, p = 0,0256; NH–IMRangio 3: r = –0,3326, Rho = 0,1106, p = 0,0336). Finally, Bland–Altman plot analysis showed good agreement between NH–IMRangio 1 and 3, while NH–IMRangio 2 showed a consistent bias of –5 units against both NH–IMRangio 1 and NH–IMRangio 2 with increasing difference at higher absolute values.

Conclusion

CMD, assessed with NH–IMRangio, is a common finding in TTS and it is inversely correlate with LVEF dysfunction. The available formulas for NH–IMRangio computation have a substantial superimposable diagnostic performance in assessing CMD.

Intrahepatic cholestasis of pregnancy resistant to both therapeutic plasma exchange and albumin dialysis

Intrahepatic cholestasis in pregnancy (ICP) represents, depending on its severity, a serious risk for the fetus. Those cases with unusually high bile acid levels may be resistant to pharmaceutical treatment and can be treated with plasma exchange or albumin dialysis. However, the success rate of these therapeutic options and the factors influencing therapeutic response are unknown. Furthermore, if these options fail to improve ICP and serum bile acid levels are very high (>200 μm/L), there are no clear recommendations when delivery should be planned. Here, we report a patient with severe ICP resistant to both therapeutic plasma exchange and albumin dialysis. Caesarean section was performed at 32 weeks of gestation followed by rapid remission of ICP.

The diagnostic value of core needle biopsy in cervical cancer: A retrospective analysis

Cervical carcinoma is a major cause of morbidity and mortality among women worldwide. Histological subtype, lymphovascular space invasion and tumor grade could have a prognostic and predictive value for patients’ outcome and the knowledge of these histologic characteristics may influence clinical decision making. However, studies evaluating the diagnostic value of various biopsy techniques regarding these parameters of cervical cancer are scarce. We reviewed 318 cases of cervical carcinoma with available pathology reports from preoperative core needle biopsy (CNB) assessment and from final postoperative evaluation of the hysterectomy specimen. Setting the postoperative comprehensive pathological evaluation as reference, we analysed CNB assessment of histological tumor characteristics. In addition, we performed multivariable logistic regression to identify factors influencing the accuracy in identifying LVSI and tumor grade. CNB was highly accurate in discriminating histological subtype. Sensitivity and specificity were 98.8% and 89% for squamous cell carcinoma, 92.9% and 96.6% for adenocarcinoma, 33.3% and 100% in adenosquamous carcinoma respectively. Neuroendocrine carcinoma was always recognized correctly. The accuracy of the prediction of LVSI was 61.9% and was positively influenced by tumor size in preoperative magnetic resonance imaging and negatively influenced by strong peritumoral inflammation. High tumor grade (G3) was diagnosed accurately in 73.9% of cases and was influenced by histological tumor type. In conclusion, CNB is an accurate sampling technique for histological classification of cervical cancer and represents a reasonable alternative to other biopsy techniques.

The Importance of Clinical Examination under General Anesthesia: Improving Parametrial Assessment in Cervical Cancer Patients

Simple Summary

In most cases, the treatment strategy (radiation or surgery) in cervical cancer patients depends on whether the parametrium shows tumor involvement. Traditionally, clinical pelvic examination under general anesthesia (EUA) has been used to determine whether tumor spread into the parametrium is present. During the recent decade, however, magnetic resonance imaging (MRI) has been increasingly used to determine whether parametrial tumor extension is present, and several studies have indicated that MRI might be superior to EUA. In this study, we demonstrate that EUA still plays an important role in pre-therapeutic evaluation of cervical cancer patients, and that display of MR images in the operating room (augmented EUA) achieves superior results in predicting parametrial tumor spread when comparted to MRI alone, especially in larger tumors. Best predictive results were observed in cases when radiologists and gynecological oncologists agreed on parametrial status, highlighting the importance of interdisciplinary patient assessment.

Abstract

Background: Parametrial tumor involvement is an important prognostic factor in cervical cancer and is used to guide management. Here, we investigate the diagnostic value of clinical examination under general anesthesia (EUA) and magnetic resonance imaging (MRI) in determining parametrial tumor spread. Methods: Post-operative pathological findings of 400 patients with primary cervical cancer were compared to the respective MRI data and the results from EUA. The gynecological oncologist had access to the MR images during clinical assessment (augmented EUA, aEUA). Results: Pathologically proven parametrial tumor invasion was present in 165 (41%) patients. aEUA exhibited a higher accuracy than MRI alone (83% vs. 76%; McNemar’s odds ratio [OR] = 2.0, 95%CI 1.25–3.27, p = 0.003). Although accuracy was not affected by tumor size in aEUA, MRI was associated with a lower accuracy in tumors ≥2.5 cm (OR for a correct diagnosis compared to smaller tumors 0.22, p < 0.001). There was also a decrease in specificity when evaluating parametrial invasion by MRI in tumors ≥2.5 cm in diameter (p < 0.0001) compared to smaller tumors (< 2.5 cm). Body mass index had no influence on performance of either method. Conclusions: aEUA has the potential to increase the diagnostic accuracy of MRI in determining parametrial tumor involvement in cervical cancer patients.

The diagnostic value of core needle biopsy in cervical cancer: A retrospective analysis

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Background: The aim of this retrospective study was to evaluate the accuracy, sensitivity, specificity, and predictive values of preoperative core needle biopsy (CNB) assessment of histological characteristics in primary cervical cancer. Methods: We reviewed 318 cases of primary cervical carcinoma with available pathology reports from preoperative CNB assessment and from final postoperative evaluation of the hysterectomy specimen. Setting the postoperative comprehensive pathological evaluation as reference, we analysed CNB assessment of histological tumor characteristics. In addition, we performed multivariable logistic regression to identify factors influencing the accuracy in identifying lymphovascular space invasion (LVSI) and tumor grade. Results: CNB was highly accurate in discriminating histological subtype. Sensitivity and specificity were 98.8% and 89% for squamous cell carcinoma (SCC), 92.9% and 96.6% for adenocarcinoma (AC), 33.3% and 100% in adenosquamous carcinoma respectively. Neuroendocrine carcinoma was always recognized correctly. The accuracy of the prediction of lymphovascular space invasion (LVSI) was 61.9% and was positively influenced by tumor size in preoperative MRI and negatively influenced by strong peritumoral inflammation. High tumor grade was diagnosed accurately in 73.9% of cases and was influenced by histological tumor type. Conclusions: CNB is an accurate sampling technique for histological classification of cervical cancer and represents a reasonable alternative to other biopsy techniques. Factors such as peritumoral inflammation, tumor size or tumor subtype may influence the accuracy of histologic Evaluation and should be taken into account when interpreting the results.

Parametrial evaluation in cervical cancer by magnetic resonance imaging and clinical examination: Analysis of data from the prospective Leipzig School MMR study

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Parametrial evaluation in cervical cancer by magnetic resonance imaging and clinical examination Background: In cervical cancer patients, assessment of parametrial tumor extension is important for staging and treatment planning. The 2019 cervical cancer guideline published by the Féderation Internationale de Gynécologie et d’Obstétrique (FIGO) for the first time includes recommendations for usage of magnetic resonance imaging (MRI) in this setting. However, valid data regarding the accuracy of this method, especially in patients with advanced disease, are sparce. The objective of this investigation was to compare the accuracy of parametrial assessment in cervical cancer patients using MRI and clinical examination under general anesthesia. Methods: A retrospective cohort study based on data from the prospective monocentric observational Leipzig School Mesometrial Resection study was conducted. Cervical cancer patients staged FIGO IB1 to FIGO IVA who underwent primary surgery between 1999 and 2017 were included. Data from pathological specimen of these patients was compared to the MRI findings and the results from clinical examination under general anesthesia. The gynecological oncologist had access to the MR images during clinical assessment. We calculated sensitivities, specificities, and predictive values for both examination methods. We performed logistic regression modelling to determine factors influencing the accuracy of either method. Results: 400 women were included. Pathologically proven parametrial tumor invasion was present in 165 (41%) patients. Examination under anesthesia augmented by intraoperative display of MR images exhibited a higher accuracy (83%) as compared to MRI alone (76%; McNemar’s odds ratio = 2.0, 95%CI 1.25 – 3.27, p = 0.003). While accuracy was not affected by tumor size in clinical examination, MRI was associated with a significant drop in accuracy in tumors ≥ 2.5 cm (univariable logistic regression, OR for a correct diagnosis compared to smaller tumors 0.22, p < 0.001). This association remained significant in a multivariable model. There was also a significant decrease in specificity when evaluating parametrial invasion by MRI in tumors ≥ 2.5 cm in diameter (p < 0.0001). Body mass index had no influence on performance of either method. Accuracy was significantly higher when test results were concordant (OR 7.5 and 6.0 on univariable and multivariable regression modelling, respectively, p < 0.0001 in both cases). Conclusions: Clinical evaluation of the parametrium by pelvic examination under anesthesia in conjunction with intraoperative presentation of MR images leads to more accurate staging in cervical cancer patients as compared to magnetic resonance imaging alone. Clinical examination should therefore remain an integral part of parametrial assessment in cervical cancer patients.

Recommended pre-analytical plasma glucose sampling methodology may distort gestational diabetes mellitus prevalence: implications for diagnostic thresholds

AIM

Current International Association of the Diabetes and Pregnancy Study Groups/World Health Organization gestational diabetes mellitus (GDM) diagnostic thresholds are based on a landmark study in which the pre-analytical plasma glucose sampling methodology is unclear. Worldwide, plasma glucose pre-analytical sampling methodology practices are divergent. We considered the effects of pre-analytical plasma glucose sampling methodology on GDM prevalence and gestational outcomes.

METHODS

This is a retrospective observational cohort study of 1178 pregnant women undergoing an oral glucose tolerance test (OGTT). Of the 1178 pregnant women, a subset of 892 non-GDM women with singleton births undergoing OGTT between 24 and 28 weeks' gestation were investigated for large for gestation age (LGA) outcomes. OGTT were determined using traditional methods (sodium fluoride tubes batched at roomed temperature). We modelled the potential effects of using a recommended pre-analytical plasma glucose methodology (lyophilized citrate tubes) on GDM prevalence.

RESULTS

The GDM prevalence in our cohort was 13.5%. The incidence of LGA showed a linear association with maternal plasma glucose that was similar to the association observed in the Hyperglycemia and Adverse Pregnancy Outcome study. Frequency of LGA exceeded 10% at HAPO glucose category 4 (fasting, 4.8 to 4.9 mmol/l; 1-h, 8.7 to 9.5 mmol/l) for fasting and 1-h plasma glucose. The use of a recommended pre-analytical method is projected to increase the prevalence of GDM to 39.2%.

CONCLUSION

We challenge the consensus that recommended pre-analytical plasma glucose methodologies are optimal for the accurate diagnosis of GDM. Recommended pre-analytical plasma glucose methods may profoundly over-diagnose GDM. Centres using recommended pre-analytical plasma glucose methodologies may need to reappraise their diagnostic thresholds.

Activity and safety of crizotinib in patients with advanced clear-cell sarcoma with MET alterations: European Organization for Research and Treatment of Cancer phase II trial 90101 'CREATE'

Background

Clear-cell sarcoma (CCSA) is an orphan malignancy, characterized by a specific t(12;22) translocation, leading to rearrangement of the EWSR1 gene and overexpression of MET. We prospectively investigated the efficacy and safety of the tyrosine kinase inhibitor crizotinib in patients with advanced or metastatic CCSA.

Patients and methods

Patients with CCSA received oral crizotinib 250 mg twice daily. Primary end point was objective response rate (ORR), secondary end points included duration of response, disease control rate (DCR), progression-free survival (PFS), progression-free rate (PFR), overall survival (OS), OS rate and safety. The study design focused on MET+ disease with documented rearrangement of the EWSR1 gene by fluorescence in situ hybridization.

Results

Among 43 consenting patients with the local diagnosis of CCSA, 36 had centrally confirmed CCSA, 28 of whom were eligible, treated and assessable. Twenty-six out of the 28 patients had MET+ disease, of whom one achieved a confirmed partial response and 17 had stable disease (SD) (ORR 3.8%, 95% confidence interval: 0.1-19.6). Further efficacy end points in MET+ CCSA were DCR: 69.2% (48.2% to 85.7%), median PFS: 131 days (49-235), median OS: 277 days (232-442). The 3-, 6-, 12- and 24-month PFR was 53.8% (34.6-73.0), 26.9% (9.8-43.9), 7.7% (1.3-21.7) and 7.7% (1.3-21.7), respectively. Among two assessable MET- patients, one had stable disease and one had progression. The most common treatment-related adverse events were nausea [18/34 (52.9%)], fatigue [17/34 (50.0%)], vomiting [12/34 (35.3%)], diarrhoea [11/34 (32.4%)], constipation [9/34 (26.5%)] and blurred vision [7/34 (20.6%)].

Conclusions

The PFS with crizotinib in MET+ CCSA is similar to results achieved first-line in non-selected metastatic soft tissue sarcomas with single-agent doxorubicin. The PFS is similar to results achieved with pazopanib in previously treated sarcoma patients.

Clinical trial number

EORTC 90101, EudraCT number 2011-001988-52, NCT01524926.

TBX1 is responsible for cardiovascular defects in velo-cardio-facial/DiGeorge syndrome

Velo-cardio-facial syndrome (VCFS)/DiGeorge syndrome (DGS) is a human disorder characterized by a number of phenotypic features including cardiovascular defects. Most VCFS/DGS patients are hemizygous for a 1.5-3.0 Mb region of 22q11. To investigate the etiology of this disorder, we used a cre-loxP strategy to generate mice that are hemizygous for a 1.5 Mb deletion corresponding to that on 22q11. These mice exhibit significant perinatal lethality and have conotruncal and parathyroid defects. The conotruncal defects can be partially rescued by a human BAC containing the TBX1 gene. Mice heterozygous for a null mutation in Tbx1 develop conotruncal defects. These results together with the expression patterns of Tbx1 suggest a major role for this gene in the molecular etiology of VCFS/DGS.

The DNA mismatch repair genes Msh3 and Msh6 cooperate in intestinal tumor suppression

Repair of mismatches in DNA in mammalian cells is mediated by a complex of proteins that are members of two highly conserved families of genes referred to as MutS and MutL homologues. Germline mutations in several members of these families, MSH2, MSH6, MLH1, and PMS2, but not MSH3, are responsible for hereditary non-polyposis colorectal cancer. To examine the role of MSH3, we generated a mouse with a null mutation in this gene. Cells from Msh3-/- mice are defective in repair of insertion/ deletion mismatches but can repair base-base mismatches. Msh3-/- mice develop tumors at a late age. When the Msh3-/- and Msh6-/- mutations are combined, the tumor predisposition phenotype is indistinguishable from Msh2-/- or Mlh1-/- mice. These results suggest that MSH3 cooperates with MSH6 in tumor suppression.

Postgastrulation Smad2-deficient embryos show defects in embryo turning and anterior morphogenesis

SMAD2 is a member of the transforming growth factor beta and activin-signaling pathway. To examine the role of Smad2 in postgastrulation development, we independently generated mice with a null mutation in this gene. Smad2-deficient embryos die around day 7.5 of gestation because of failure of gastrulation and failure to establish an anterior-posterior (A-P) axis. Expression of the homeobox gene Hex (the earliest known marker of the A-P polarity and the prospective head organizer) was found to be missing in Smad2-deficient embryos. Homozygous mutant embryos and embryonic stem cells formed mesoderm derivatives revealing that mesoderm induction is SMAD2 independent. In the presence of wild-type extraembryonic tissues, Smad2-deficient embryos developed beyond 7.5 and up to 10.5 days postcoitum, demonstrating a requirement for SMAD2 in extraembryonic tissues for the generation of an A-P axis and gastrulation. The rescued postgastrulation embryos showed malformation of head structures, abnormal embryo turning, and cyclopia. Our results show that Smad2 expression is required at several stages during embryogenesis.

Tumorigenesis in Mlh1 and Mlh1/Apc1638N mutant mice

An3 1 KAL I MutL homologue 1 (MLH1) is a member of the family of proteins required for DNA mismatch repair. Germ-line mutations in MLH1 lead to the cancer susceptibility syndrome hereditary nonpolyposis colorectal cancer (HNPCC). We generated mice carrying a null mutation in the Mlh1 gene. We showed that mice heterozygous and homozygous for the Mlh1 gene are predisposed to developing tumors of the gastrointestinal (GI) tract, lymphomas, and a number of other tumor types. We also examined the role of adenomatous polyposis coli gene (Apc) gene mutations in the GI tumors of Mlh1 mutant mice by different methods and showed that the GI tumors in Mlh1 mice express little or no adenomatous polyposis coli protein. When an Apc gene mutation was bred into the Mlh1 mutant mice, the GI tumor incidence increased 40-100-fold. The wild-type Apc allele in these tumors was found to contain mutations. Together, these results show that we have developed two mouse models for human HNPCC and that the mechanisms of tumor development in the GI tract of these mice involve loss of Apc gene function in a manner very similar to that seen in the GI tumors of HNPCC.

Mammalian MutS homologue 5 is required for chromosome pairing in meiosis

MSH5 (MutS homologue 5) is a member of a family of proteins known to be involved in DNA mismatch repair. Germline mutations in MSH2, MLH1 and GTBP (also known as MSH6) cause hereditary non-polyposis colon cancer (HNPCC) or Lynch syndrome. Inactivation of Msh2, Mlh1, Gtmbp (also known as Msh6) or Pms2 in mice leads to hereditary predisposition to intestinal and other cancers. Early studies in yeast revealed a role for some of these proteins, including Msh5, in meiosis. Gene targeting studies in mice confirmed roles for Mlh1 and Pms2 in mammalian meiosis. To assess the role of Msh5 in mammals, we generated and characterized mice with a null mutation in Msh5. Msh5-/- mice are viable but sterile. Meiosis in these mice is affected due to the disruption of chromosome pairing in prophase I. We found that this meiotic failure leads to a diminution in testicular size and a complete loss of ovarian structures. Our results show that normal Msh5 function is essential for meiotic progression and, in females, gonadal maintenance.

Chromosomal deletions around the albino locus in the mouse cause loss of hormone-inducible expression of the unlinked structural gene encoding cytosolic aspartate aminotransferase

A group of genes in the mouse encoding liver-specific gluconeogenic enzymes and mapping on different chromosomes lose their normal competence for hormone-inducible expression in animals homozygous for chromosomal deletions around the albino locus on chromosome 7. The basal expression of these same genes remains normal. In previous investigations, glucocorticoid hormones as well as their receptors were found to be normal in the deletion homozygotes. The results reported here identify an additional unlinked structural gene whose regulation appears to be affected by the deletions--i.e., that encoding cytosolic aspartate aminotransferase, a housekeeping gene that participates in gluconeogenesis in the liver. In normal mice, its mRNA level increases sharply at birth, specifically in the liver, and can be increased even further by dexamethasone and cAMP treatment. These increases fail to occur in mice homozygous for the specific deletions in chromosome 7. Interestingly, prenatally at 18-19 days of gestation, the gene is expressed at the same basal level in liver and brain of both normal and mutant mice. These observations strengthen the evidence implicating the deleted gene(s) as an essential factor(s) in the normal mechanisms of hormone-inducible expression of particular unlinked structural genes.

Selective loss of a DNase I hypersensitive site upstream of the tyrosine aminotransferase gene in mice homozygous for lethal albino deletions

Several overlapping chromosomal deletions spanning the albino locus in the mouse cause perinatal lethality when homozygous and a block in the transcriptional induction of various unlinked hepatocyte-specific genes. Studies of such lethal albino deletion homozygotes in perinatal stages revealed a deficiency in the transcriptional inducibility of the tyrosine aminotransferase (TAT) gene by glucocorticoids; yet, glucocorticoid receptor and hormone levels were shown to be unaffected. To identify a molecular defect underlying the failure of inducible expression, we examined the chromatin structure of the TAT gene. Whereas in wild-type animals the TAT promoter becomes DNase I hypersensitive at birth, such hypersensitivity fails to develop in lethal albino deletion homozygotes. By contrast, the deletions do not affect the appearance of three DNase I-hypersensitive sites upstream of the TAT promoter in the liver, nor do they affect two hypersensitive sites upstream of the expressed alpha-fetoprotein gene. These findings demonstrate that the abnormality of chromatin structure identified in lethal albino deletion homozygotes occurs on a highly selective basis. Specifically, normal differentiation of the TAT promoter chromatin appears to depend directly or indirectly on the action and product of a gene mapping within the deleted region.

Regulatory genes linked to the albino locus in the mouse confer competence for inducible expression on the structural gene encoding serine dehydratase

A cluster of unlinked genes encoding gluconeogenic enzymes in the mouse is characterized by the failure of normal hormone-inducible expression in animals homozygous for one of several overlapping deletions mapping on chromosome 7 near the albino locus. Previous investigations have shown hormones and their receptors to be normal in the mutants and therefore not responsible for the abnormalities of inducibility. Instead, these studies have implicated a possible failure of the affected structural enzyme genes themselves to attain during prenatal development the competence for inducible gene expression. The results reported here add serine dehydratase (EC 4.2.1.13) and its structural gene to the affected group of gluconeogenic enzymes and their genes. Even though, in deletion homozygotes, serine dehydratase is expressed normally on the constitutive level, hormone-inducible expression fails to develop. The abnormality appears to reside in a defect of prenatal differentiation of cis-acting regulatory elements of the structural gene essential in the pathway of inducible gene expression.