Disruption of Gen1 Causes Congenital Anomalies of the Kidney and Urinary Tract in Mice

GEN1 as a risk factor for human congenital anomalies of the kidney and urinary tract

BACKGROUND

Congenital anomalies of the kidney and urinary tract (CAKUT) are prevalent birth defects. Although pathogenic CAKUT genes are known, they are insufficient to reveal the causes for all patients. Our previous studies indicated GEN1 as a pathogenic gene of CAKUT in mice, and this study further investigated the correlation between GEN1 and human CAKUT.

METHODS

In this study, DNA from 910 individuals with CAKUT was collected; 26 GEN1 rare variants were identified, and two GEN1 (missense) variants in a non-CAKUT group were found. Mainly due to the stability results of the predicted mutant on the website, in vitro, 10 variants (eight CAKUT, two non-CAKUT) were selected to verify mutant protein stability. In addition, mainly based on the division of the mutation site located in the functional region of the GEN1 protein, 8 variants (six CAKUT, two non-CAKUT) were selected to verify enzymatic hydrolysis, and the splice variant GEN1 (c.1071 + 3(IVS10) A > G) was selected to verify shear ability. Based on the results of in vitro experiments and higher frequency, three sites with the most significant functional change were selected to build mouse models.

RESULTS

Protein stability changed in six variants in the CAKUT group. Based on electrophoretic mobility shift assay of eight variants (six CAKUT, two non-CAKUT), the enzymatic hydrolysis and DNA-binding abilities of mutant proteins were impaired in the CAKUT group. The most serious functional damage was observed in the Gen1 variant that produced a truncated protein. A mini-gene splicing assay showed that the variant GEN1 (c.1071 + 3(IVS10) A > G) in the CAKUT group significantly affected splicing function. An abnormal exon10 was detected in the mini-gene splicing assay. Point-mutant mouse strains were constructed (Gen1: c.1068 + 3 A > G, p.R400X, and p.T105R) based on the variant frequency in the CAKUT group and functional impairment in vitro study and CAKUT phenotypes were replicated in each.

CONCLUSION

Overall, our findings indicated GEN1 as a risk factor for human CAKUT.

Whole exome sequencing reveals novel candidate variants for endometriosis utilizing multiple affected members in a single family

BACKGROUND

Endometriosis is an estrogen-dependent, chronic inflammatory disease that affects 10% of women during the reproductive ages. Despite the estimated 50% heritability for the condition, only 26% was associated with common genetic variants. Thus, necessity of identifying rare variants for the missing heritability is implicated in the literature. Therefore, our study aimed to identify novel rare genetic variants involved in the pathogenesis of endometriosis utilizing a family of multiple affected members.

METHODS

A family composed of four affected women along with their two unaffected mothers were recruited at a single gynecology and infertility clinic specialized in endometriosis. All patients presented with endometriomas, which was visualized by transvaginal ultrasonography. Two affected individuals had received laparoscopic endometrioma excision and therefore were diagnosed with recurrent disease. One mother had a history of endometrial serous adenocarcinoma (ESC) for which she underwent hysterectomy with bilateral oophorectomy. Three endometriosis cases were whole exome sequenced on Illumina NextSeq 550 platform with an average of 90% coverage. Candidate genes were confirmed by Sanger sequencing and followed-up with family segregation.

RESULTS

Novel rare variants were identified in TNFRSF1B (NM_001066.3: c.1072G>A, p.(Ala358Thr)) and GEN1 (NM_001130009.3: c.1574C>T, p.(Ser525Leu)) as possible genetic causes of endometriosis. A third novel rare variant was identified in CRABP1 (NM_004378.3:c.54G>C, p.(Glu18Asp)) only on the mother with ESC history and her daughters.

CONCLUSION

Novel candidate genetic variants that might contribute to endometriosis were suggested that need replication through independent cohorts or validation by functional studies. The family has also received genetic counseling and that the affected daughters are on clinical follow-up, accordingly.

The genetics and pathogenesis of CAKUT

Congenital anomalies of the kidney and urinary tract (CAKUT) comprise a large variety of malformations that arise from defective kidney or urinary tract development and frequently lead to kidney failure. The clinical spectrum ranges from severe malformations, such as renal agenesis, to potentially milder manifestations, such as vesicoureteral reflux. Almost 50% of cases of chronic kidney disease that manifest within the first three decades of life are caused by CAKUT. Evidence suggests that a large number of CAKUT are genetic in origin. To date, mutations in ~54 genes have been identified as monogenic causes of CAKUT, contributing to 12-20% of the aetiology of the disease. Pathogenic copy number variants have also been shown to cause CAKUT and can be detected in 4-11% of patients. Furthermore, environmental and epigenetic factors can increase the risk of CAKUT. The discovery of novel CAKUT-causing genes is challenging owing to variable expressivity, incomplete penetrance and variable genotype-phenotype correlation. However, such a discovery could ultimately lead to improvements in the accurate molecular genetic diagnosis, assessment of prognosis and multidisciplinary clinical management of patients with CAKUT, potentially including personalized therapeutic approaches.

Inhibition of MAPK/ERK pathway activation rescues congenital anomalies of the kidney and urinary tract (CAKUT) in Robo2PB/+ Gen1PB/+ mice

Congenital anomalies of the kidney and urinary tract (CAKUT) have been attributed to genetic and environmental factors. However, monogenic and copy number variations cannot sufficiently explain the cause of the majority of CAKUT cases. Multiple genes through various modes of inheritance may lead to CAKUT pathogenesis. We previously showed that Robo2 and Gen1 coregulated the germination of ureteral buds (UB), significantly increasing CAKUT incidence. Furthermore, MAPK/ERK pathway activation is the central mechanism of these two genes. Thus, we explored the effect of the MAPK/ERK inhibitor U0126 in the CAKUT phenotype in Robo2^PB/+Gen1^PB/+ mice. Intraperitoneal injection of U0126 during pregnancy prevented the development of the CAKUT phenotype in Robo2^PB/+Gen1^PB/+ mice. Additionally, a single dose of 30 mg/kg U0126 on day 10.5 embryos (E10.5) was most effective for reducing CAKUT incidence and ectopic UB outgrowth in Robo2^PB/+Gen1^PB/+ mice. Furthermore, embryonic kidney mesenchymal levels of p-ERK were significantly decreased on day E11.5 after U0126 treatment, along with decreased cell proliferation index PHH3 and ETV5 expression. Collectively, Gen1 and Robo2 exacerbated the CAKUT phenotype in Robo2^PB/+Gen1^PB/+ mice through the MAPK/ERK pathway, increasing proliferation and ectopic UB outgrowth.

Robo2 and Gen1 Coregulate Ureteric Budding by Activating the MAPK/ERK Signaling Pathway in Mice

Congenital anomalies of the kidney and urinary tract (CAKUT) are some of the most common developmental defects and have a complicated etiology, indicating an interaction of (epi-) genetic and environmental factors. Single gene mutations and copy number variations (CNVs) do not explain most cases of CAKUT, and simultaneous contributions of more than one gene (di-, oligo-, or polygenic effects; i.e., complex genetics) may lead to the pathogenesis of CAKUT. Robo2 plays a key role in regulating ureteric bud (UB) formation in the embryo, with mutations leading to supernumerary kidneys. Gen1 is a candidate gene associated with CAKUT because of its important role in early metanephric development in mice. We established a mouse model with double disruption of Robo2 and Gen1 using a piggyBac transposon and found that double gene mutation led to significantly increased CAKUT phenotypes in Robo2^PB/+Gen1^PB/+ mouse offspring, especially a duplicated collecting system. Increased ectopic UB formation was observed in the Robo2^PB/+Gen1^PB/+ mice during the embryonic period. Robo2 and Gen1 exert synergistic effects on mouse kidney development, promoting cell proliferation by activating the GDNF/RET pathway and downstream MAPK/ERK signaling. Our findings provide a disease model for CAKUT as an oligogenic disorder.

Disruption of Gen1 causes ectopic budding and kidney hypoplasia in mice

Congenital anomalies of the kidney and urinary tract (CAKUT) are a family of often-concurrent diseases with various anatomical spectra. Null-mutant Gen1 mice frequently develop multiple urinary phenotypes, most commonly duplex kidneys, and are ideal subjects for research on ectopic budding in CAKUT development. The upper and lower kidney poles of the Gen1^PB/PB mouse were examined by histology, immunofluorescence, and immunohistochemistry. The newborn Gen1^PB/PB mouse lower poles were significantly more hypoplastic than the corresponding upper poles, with significantly fewer glomeruli. On embryonic day 14.5, immediately before first urine formation, the upper pole kidney was already larger than the lower pole kidney. In vivo and in vitro, embryonic kidney upper poles had more ureteric buds than lower poles. Gen1^PB/PB embryos exhibited ectopic ureteric buds, usually near the original budding site, occasionally far away, or, rarely, derived from the primary budding site. Therefore, ectopia of the ureteric buds is the core of CAKUT formation. Further studies will be needed to investigate the regulatory roles of these genes in initial ureteric budding and subsequent ontogenesis during metanephros development.

Intrauterine Low-Protein Diet Exacerbates Abnormal Development of the Urinary System in Gen1-Mutant Mice

BACKGROUND

Gen1 mutation can cause various phenotypes of congenital anomaly of the kidney and urinary tract (CAKUT). An intrauterine low-protein isocaloric diet can also cause CAKUT phenotypes in offspring. However, single factors such as gene mutation or abnormal environmental factor during pregnancy can only explain part of the pathogenesis of CAKUT.

OBJECTIVES

A low-protein isocaloric diet was fed to Gen1-mutant mice throughout pregnancy to establish a Gen1-mutant mouse model exposed to a low-protein isocaloric intrauterine environment. The mice were divided into 4 groups: normal (22%) protein diet (ND) + wild-type mice (CON group), ND + Gen1^PB/+ mice (Gen1^PB/+ group), low (6%)-protein isocaloric diet (LD) + wild-type mice (LD group), and the LD + Gen1^PB/+ groups.

METHODS

The experimental design included observing proportion and distribution of CAKUT phenotypes of neonatal mice; evaluating the number of ureteric buds (UBs) on embryonic day (E) 11.5, the location of UBs on E11.5, and length of the common nephric duct (CND); isolating embryonic kidneys on E11.5 from the Gen1^PB/+ group and culturing embryonic kidneys in medium containing 10% serum or serum-free medium to observe the branching of UBs; and detecting the p-PLCγ, p-Akt, and p-ERK1/2 in UBs and CND on E11.5, as well as the apoptosis and proliferation of tissues by immunofluorescence staining.

RESULTS

We found that the incidence of CAKUT in offspring of Gen1^PB/+ mice under an intrauterine low-protein isocaloric diet environment was significantly increased, and a duplicated collecting system was the dominant phenotype of CAKUT. During the early stage of metanephric development, ectopic protrusion of UBs may appear and lower locations of UBs in Gen1^PB/+ mice under an intrauterine low-protein isocaloric diet environment and the number of UB branches in the serum-free culture condition significantly decreased. Further examination revealed that p-PLCγ signaling and tissue apoptosis were abnormal in UBs and the CND at the early stage of kidney development.

CONCLUSIONS

The aforementioned findings suggest that an intrauterine low-protein isocaloric diet can aggravate the occurrence of CAKUT in Gen1-mutant mice, which might affect key steps in the metanephric development, such as the protrusion of UBs, which might be related to mediate UBs and CND apoptosis through p-PLCγ signaling.

Mouse Models for Deciphering the Impact of Homologous Recombination on Tumorigenesis

Homologous recombination (HR) is a fundamental evolutionarily conserved process that plays prime role(s) in genome stability maintenance through DNA repair and through the protection and resumption of arrested replication forks. Many HR genes are deregulated in cancer cells. Notably, the breast cancer genes BRCA1 and BRCA2, two important HR players, are the most frequently mutated genes in familial breast and ovarian cancer. Transgenic mice constitute powerful tools to unravel the intricate mechanisms controlling tumorigenesis in vivo. However, the genes central to HR are essential in mammals, and their knockout leads to early embryonic lethality in mice. Elaborated strategies have been developed to overcome this difficulty, enabling one to analyze the consequences of HR disruption in vivo. In this review, we first briefly present the molecular mechanisms of HR in mammalian cells to introduce each factor in the HR process. Then, we present the different mouse models of HR invalidation and the consequences of HR inactivation on tumorigenesis. Finally, we discuss the use of mouse models for the development of targeted cancer therapies as well as perspectives on the future potential for understanding the mechanisms of HR inactivation-driven tumorigenesis in vivo.

Gen1 mutation caused kidney hypoplasia and defective ureter-bladder connections in mice

Limited genetic factors were uncovered for the development of congenital anomalies of the kidney and urinary tract (CAKUT). We previously reported that a Holliday junction resolvase Gen1 was essential for early metanephric development in mice. This comprehensive follow-up study focused on the roles of Gen1 in late metanephric development. We found that Gen1 mutation impaired the late development of both kidney and urinary tract. In vivo and ex-vivo kidney primordia culture confirmed decreased ureteric bud branching in Gen1 mutants, which consequently caused hypoplasia. We also observed abnormal urinary tract development. Programmed apoptosis at the end of nephric duct disappeared in Gen1 mutants, which caused abnormal ureter-bladder connections, leading to vesicoureteral reflux (VUR) or ureterovesical junction obstruction (UVJO). Mechanistically, RNA-seq analysis proved that Gen1 mutation impaired the expression of multiple regulatory genes for the metanephric development, including Six2. Taken together, our study provides more insight into the roles of Gen1 in the development of the kidney and urinary tract, which may have potential clinical significance in the treatment and/or prevention of CAKUT.

Gen1 Modulates Metanephric Morphology Through Retinoic Acid Signaling

Congenital anomalies of the kidney and urinary tract (CAKUT) are the leading cause of end-stage renal disease in children. Our group has discovered that Holliday Junction resolvase gene Gen1 is a potential candidate gene for CAKUT. Gen1 mutant mice showed CAKUT phenotypes similar to those observed in retinoic acid (RA)-deficient models. The expression of Raldh2, which encodes the key enzyme in RA synthesis, was reduced in Gen1 mutant metanephros through RNA sequencing. By real-time reverse transcription-PCR, the expression of both Raldh2 and downstream Ret was reduced in embryonic day (E) 11.5 Gen1 mutant ureters and E13.5 kidneys, and expression of RA receptor alpha was decreased in E13.5 Gen1 mutant ureters and kidneys. Further studies showed that all-trans retinoic acid (ATRA) rescued solitary kidney phenotype and improved ureteric branching; ATRA should be administered after ureteric budding to avoid increasing the incidence of ectopic budding in Gen1 mutants. Luciferase intensity of RA response element was lower in CHO-K1 cells transfected with Gen1 siRNA than in those transfected with scrambled RNA, and this inhibitory effect could be reversed by ATRA. These findings indicate that Gen1 mutation can result in renal malformation through RA signaling and Gen1-loss-induced CAKUT can be partly rescued by ATRA.