Urogenital syndrome (us): a developmental mutation on chromosome 2 of the mouse

Development, Pathogenesis, and Regeneration of the Intervertebral Disc: Current and Future Insights Spanning Traditional to Omics Methods

The intervertebral disc (IVD) is the fibrocartilaginous joint located between each vertebral body that confers flexibility and weight bearing capabilities to the spine. The IVD plays an important role in absorbing shock and stress applied to the spine, which helps to protect not only the vertebral bones, but also the brain and the rest of the central nervous system. Degeneration of the IVD is correlated with back pain, which can be debilitating and severely affects quality of life. Indeed, back pain results in substantial socioeconomic losses and healthcare costs globally each year, with about 85% of the world population experiencing back pain at some point in their lifetimes. Currently, therapeutic strategies for treating IVD degeneration are limited, and as such, there is great interest in advancing treatments for back pain. Ideally, treatments for back pain would restore native structure and thereby function to the degenerated IVD. However, the complex developmental origin and tissue composition of the IVD along with the avascular nature of the mature disc makes regeneration of the IVD a uniquely challenging task. Investigators across the field of IVD research have been working to elucidate the mechanisms behind the formation of this multifaceted structure, which may identify new therapeutic targets and inform development of novel regenerative strategies. This review summarizes current knowledge base on IVD development, degeneration, and regenerative strategies taken from traditional genetic approaches and omics studies and discusses the future landscape of investigations in IVD research and advancement of clinical therapies.

Spontaneous one-kidney rats are more susceptible to develop hypertension by DOCA-NaCl and subsequent kidney injury compared with uninephrectomized rats

There is little clinical data of how hypertension may influence individuals with nephron deficiency in the context of being born with a single kidney. We recently developed a new rat model (the heterogeneous stock-derived model of unilateral renal agenesis rat) that is born with a single kidney and exhibits progressive kidney injury and decline in kidney function with age. We hypothesized that DOCA-salt would induce a greater increase in blood pressure and therefore accelerate the progression of kidney injury in rats born with a solitary kidney compared with rats that have undergone unilateral nephrectomy. Time course evaluation of blood pressure, kidney injury, and renal hemodynamics was performed in the following six groups of animals from weeks 13 to 18: 1) DOCA-treated rats with a solitary kidney (DOCA+S group), 2) placebo-treated rats with a solitary kidney, 3) DOCA-treated control rats with two kidneys (DOCA+C group), 4) placebo-treated control rats with two kidneys, 5) DOCA-treated rats with two kidneys that underwent uninephrectomy (DOCA+UNX8 group), and 6) placebo-treated rats with two kidneys that underwent uninephrectomy. DOCA+S rats demonstrated a significant rise (P < 0.05) in blood pressure (192 ± 4 mmHg), proteinuria (205 ± 31 mg/24 h), and a decline in glomerular filtration rate (600 ± 42 μl·min(-1)·g kidney weight(-1)) relative to the DOCA+UNX8 (173 ± 3 mmHg, 76 ± 26 mg/24 h, and 963 ± 36 μl·min(-1)·g kidney weight(-1)) and DOCA+C (154 ± 2 mmHg, 7 ± 1 mg/24 h, and 1,484 ± 121 μl·min(-1)·g kidney weight(-1)) groups. Placebo-treated groups showed no significant change among the three groups. An assessment of renal injury markers via real-time PCR/Western blot analysis and histological analysis was concordant with the measured physiological parameters. In summary, congenital solitary kidney rats are highly susceptible to the induction of hypertension compared with uninephrectomized rats, suggesting that low nephron endowment is an important driver of elevated blood pressure, hastening nephron injury through the transmission of elevated systemic blood pressure and thereby accelerating decline in kidney function.

Nephron Deficiency and Predisposition to Renal Injury in a Novel One-Kidney Genetic Model

Some studies have reported up to 40% of patients born with a single kidney develop hypertension, proteinuria, and in some cases renal failure. The increased susceptibility to renal injury may be due, in part, to reduced nephron numbers. Notably, children who undergo nephrectomy or adults who serve as kidney donors exhibit little difference in renal function compared with persons who have two kidneys. However, the difference in risk between being born with a single kidney versus being born with two kidneys and then undergoing nephrectomy are unclear. Animal models used previously to investigate this question are not ideal because they require invasive methods to model congenital solitary kidney. In this study, we describe a new genetic animal model, the heterogeneous stock-derived model of unilateral renal agenesis (HSRA) rat, which demonstrates 50%-75% spontaneous incidence of a single kidney. The HSRA model is characterized by reduced nephron number (more than would be expected by loss of one kidney), early kidney/glomerular hypertrophy, and progressive renal injury, which culminates in reduced renal function. Long-term studies of temporal relationships among BP, renal hemodynamics, and renal function demonstrate that spontaneous single-kidney HSRA rats are more likely than uninephrectomized normal littermates to exhibit renal impairment because of the combination of reduced nephron numbers and prolonged exposure to renal compensatory mechanisms (i.e., hyperfiltration). Future studies with this novel animal model may provide additional insight into the genetic contributions to kidney development and agenesis and the factors influencing susceptibility to renal injury in individuals with congenital solitary kidney.

Ectopic expression of Ptf1a induces spinal defects, urogenital defects, and anorectal malformations in Danforth's short tail mice

Danforth's short tail (Sd) is a semidominant mutation on mouse chromosome 2, characterized by spinal defects, urogenital defects, and anorectal malformations. However, the gene responsible for the Sd phenotype was unknown. In this study, we identified the molecular basis of the Sd mutation. By positional cloning, we identified the insertion of an early transposon in the Sd candidate locus approximately 12-kb upstream of Ptf1a. We found that insertion of the transposon caused overexpression of three neighboring genes, Gm13344, Gm13336, and Ptf1a, in Sd mutant embryos and that the Sd phenotype was not caused by disruption of an as-yet-unknown gene in the candidate locus. Using multiple knockout and knock-in mouse models, we demonstrated that misexpression of Ptf1a, but not of Gm13344 or Gm13336, in the notochord, hindgut, cloaca, and mesonephros was sufficient to replicate the Sd phenotype. The ectopic expression of Ptf1a in the caudal embryo resulted in attenuated expression of Cdx2 and its downstream target genes T, Wnt3a, and Cyp26a1; we conclude that this is the molecular basis of the Sd phenotype. Analysis of Sd mutant mice will provide insight into the development of the spinal column, anus, and kidney.

Caudal regression syndrome (CRS) is a congenital heterogeneous constellation of caudal anomalies that includes varying degrees of agenesis of the spinal column, anorectal malformations, and genitourinary anomalies. Its pathogenesis is unclear. However, it could be the result of excessive physiologic regression of the embryonic caudal region based on analyses of the various mouse mutants carrying caudal agenesis. Among the mouse mutants, the Danforth's short tail (Sd) mouse is considered a best model for human CRS. Sd is a semidominant mutation, characterized by spinal defects, urogenital defects, and anorectal malformations, thus showing phenotypic similarity to human CRS. Although Sd is known to map to mouse chromosome 2, little is known about the molecular nature of the mutation. Here, we demonstrate an insertion of one type of retrotransposon near the Ptf1a gene. This resulted in ectopic expression of Ptf1a gene in the caudal region of the embryo and downregulation of Cdx2 and its downstream targets, leading to characteristic phenotypes in Sd mouse. Thus, Sd mutant mice will provide insight into the development of the spinal column, anus, and kidney.

The Skt gene, required for anorectal development, is a candidate for a molecular marker of the cloacal plate

BACKGROUND AND AIMS

It has been reported that a dorsal cloacal plate defect is associated with anorectal malformations (ARMs); however, there has been very little information reported about the developmental mechanisms involved with cloacal plate formation. Danforth's short tail (Sd) mutant mice show ARMs. In our previous study, the co-presence of Skt ( Gt ) mutation, in which Skt gene is disrupted by the gene-trap vector (p-U8), increased the incidence of ARMs in Sd mutant to 100%. Our aims in this study are determining the Skt expression around the cloaca during the anorectal development and demonstrating the role of Skt gene in ARMs.

METHODS

Embryos, normal controls [+Skt ( Gt )/+Skt ( Gt )] and ARMs models [Sd Skt ( Gt )/+Skt ( Gt )], from embryonic day (E) 9.5 to E12.5, were evaluated with X-gal staining.

RESULTS

In control embryos, Skt expression was detected both in the endoderm and ectoderm of the cloacal plate from E9.5 onward. At E12.5, Skt expression was also detected in the mesenchyme neighboring the dorsal cloacal plates. In [Sd Skt ( Gt )/+Skt ( Gt )] mutant embryos, the cloacal plates failed to extend proximodistally and, consequently, the dorsal part of cloacal plate was defective at E11.5. Skt expressing cells were detected in the shortened cloacal plate and in the thickened mesenchyme dorsal to it.

CONCLUSIONS

We showed the spatial and temporal expression of Skt gene in the cloacal plate formation. This gene could be a marker for the cloacal plate during the anorectal development. Furthermore, Skt was considered to be associated with the embryogenesis of ARMs.

The floor plate is sufficient for development of the sclerotome and spine without the notochord

Danforth'sshort-tail (Sd) mouse is a semi-dominant mutation affecting the development of the vertebral column. Although the notochord degenerates completely by embryonic day 9.5, the vertebral column exists up to the lumber region, suggesting that the floor plate can substitute for notochord function. We previously established the mutant mouse line, Skt(Gt), through gene trap mutagenesis and identified the novel gene, Skt, which was mapped 0.95cM distal to the Sd locus. Taking advantage of the fact that monitoring notochordal development and genotyping of the Sd locus can be performed using the Skt(Gt) allele, we assessed the development of the vertebra, notochord, somite, floor plate and sclerotome in +-+/+-Skt(Gt), Sd-+/+-+, Sd-Skt(Gt)/+-+, Sd-Skt(Gt)/+-Skt(Gt), Sd-+/Sd-+ and Sd-Skt(Gt)/Sd-Skt(Gt) embryos. In Sd homozygous mutants with a C57BL/6 genetic background, the vertebral column was truncated in the 6th thoracic vertebra, which was more severe than previously reported. The floor plate and sclerotome developed to the level of somite before notochord degeneration and the number of remaining vertebrae corresponded well with the level of development of the floor plate and sclerotome. Defects to the sclerotome and subsequent vertebral development were not due to failure of somitogenesis. Taken together, these results suggest that the notochord induced floor plate development before degeneration, and that the remaining floor plate is sufficient for maintenance of differentiation of the somite into the sclerotome and vertebra in the absence of the notochord.

Paraxial mesoderm contributes stromal cells to the developing kidney

The development of most, if not all, tubular organs is dependent on signaling between epithelial and stromal progenitor populations. Most often, these lineages derive from different germ layers that are specified during gastrulation, well in advance of organ condensation. Thus, one of the first stages of organogenesis is the integration of distinct progenitor populations into a single embryonic rudiment. In contrast, the stromal and epithelial lineages controlling renal development are both believed to derive from the intermediate mesoderm and to be specified as the kidney develops. In this study we directly analyzed the lineage of renal epithelia and stroma in the developing chick embryo using two independent fate mapping techniques. Results of these experiments confirm the hypothesis that nephron epithelia derive from the intermediate mesoderm. Most importantly, we discovered that large populations of renal stroma originate in the paraxial mesoderm. Collectively, these studies suggest that the signals that subdivide mesoderm into intermediate and paraxial domains may play a role in specifying nephron epithelia and a renal stromal lineage. In addition, these fate mapping data indicate that renal development, like the development of all other tubular organs, is dependent on the integration of progenitors from different embryonic tissues into a single rudiment.

Genitopatellar syndrome: Expanding the phenotype and excluding mutations inLMX1B andTBX4

Genitopatellar syndrome is a newly described disorder characterized by absent/hypoplastic patellae, lower extremity contractures, urogenital anomalies, dysmorphic features, skeletal anomalies, and agenesis of the corpus callosum. More recently, cardiac anomalies and ectodermal dysplasia have been suggested as additional features of this syndrome. We report on two additional patients with genitopatellar syndrome and expand the spectrum of anomalies to include radio-ulnar synostosis. Since there exists significant overlap in the skeletal phenotype between genitopatellar syndrome and both the nail-patella and short patella syndromes, mutation screening of their causative genes, LMX1B and TBX4, was performed. Although there still does not appear to be an identifiable molecular etiology in genitopatellar syndrome, mutations in these two candidate genes have been excluded in our patients. Since both LMX1B and TBX4 are involved in a common molecular pathway, it is likely that the causative gene of genitopatellar syndrome functions within the same developmental process.

A novel murine gene, Sickle tail, linked to the Danforth's short tail locus, is required for normal development of the intervertebral disc

We established the mutant mouse line, B6;CB-SktGtAyu8021IMEG (SktGt), through gene-trap mutagenesis in embryonic stem cells. The novel gene identified, called Sickle tail (Skt), is composed of 19 exons and encodes a protein of 1352 amino acids. Expression of a reporter gene was detected in the notochord during embryogenesis and in the nucleus pulposus of mice. Compression of some of the nuclei pulposi in the intervertebral discs (IVDs) appeared at embryonic day (E) 17.5, resulting in a kinky-tail phenotype showing defects in the nucleus pulposus and annulus fibrosus of IVDs in SktGt/Gt mice. These phenotypes were different from those in Danforth's short tail (Sd) mice in which the nucleus pulposus was totally absent and replaced by peripheral fibers similar to those seen in the annulus fibrosus in all IVDs. The Skt gene maps to the proximal part of mouse chromosome 2, near the Sd locus. The genetic distance between them was 0.95 cM. The number of vertebrae in both [Sd +/+ SktGt] and [Sd SktGt/+ +] compound heterozygotes was less than that of Sd heterozygotes. Furthermore, the enhancer trap locus Etl4lacZ, which was previously reported to be an allele of Sd, was located in the third intron of the Skt gene.

Genomewide scan for anal atresia in swine identifies linkage and association with a chromosome region on Sus scrofa chromosome 1

Anal atresia is a rare and severe disorder in swine occurring with an incidence of 0.1-1.0%. A whole-genome scan based on affected half-sibs was performed to identify susceptibility loci for anal atresia. The analysis included 27 families with a total of 95 animals and 65 affected piglets among them. Animals were genotyped for 126 microsatellite markers distributed across the 18 autosomal porcine chromosomes and the X chromosome, covering an estimated 2080 cM. Single-point and multipoint nonparametric linkage scores were calculated using the computer package ALLEGRO 1.0. Significant linkage results were obtained for chromosomes 1, 3, and 12. Markers on these chromosomes and additionally on chromosomes for which candidate genes have been postulated in previous studies were subjected to the transmission disequilibrium test (TDT). The test statistic exceeded the genomewide significance level for adjacent markers SW1621 (P = 7 x 10(-7)) and SW1902 (P = 3 x 10(-3)) on chromosome 1, supporting the results of the linkage analysis. A specific haplotype associated with anal atresia that could prove useful for selection against the disorder was revealed. Suggestive linkage and association were also found for markers S0081 on chromosome 9 and SW957 on chromosome 12.

Failure of ureteric bud invasion: a new model of renal agenesis in mice

FUBI (failure of ureteric bud invasion) is a highly inbred strain of mouse with a high spontaneous incidence of uni- or bilateral renal agenesis (60%). Bilateral renal agenesis is lethal within 2 days after birth. The primary defect of FUBI is failure of the ureteric bud to penetrate into the metanephric mesenchyme at around embryonic day 11, resulting in apoptosis of metanephric cells and leading to renal agenesis on the affected side. The metanephros seemed to be normal because co-culturing of the FUBI metanephros with homologous spinal cord induced differentiation of the rudiment, but co-culturing with the homologous ureteric bud frequently did not. Genetic analysis revealed that more than two genes were involved in this malformation and we mapped one of the modifier loci, fubi1, on chromosome 2, at approximately 65 cM from the centromere. In this region, there are two possible candidate genes, Wilms' tumor 1 and formin, that play important roles in kidney development. Some of formin mutants shared a similar phenotype with FUBI; however, there was no difference in the expression of formin in embryonic kidneys between FUBI and control NFS/N mice. Studies of fubi1 congenic mice indicated that interaction of two or more loci is essential for the FUBI phenotype.

Anorectal malformations associated with enteric dysganglionosis in Danforth's short tail (Sd) mice

BACKGROUND

The spontaneous mutant Danforth's short tail (Sd) mouse has been studied over the last 60 years from the morphological, embryological, and genetic point of view. The Sd mutation affects a gene essential to notochordal development, and the Sd mouse phenotype represents an analogue of human caudal regression syndrome. The Sd/Sd mouse presents different types of anorectal malformations (ARM) and was suggested as a simple and cheap model of investigation of ARM morphology and embryology. In the current study, the Sd mouse enteric nervous system (ENS) was thoroughly investigated with specific immunohistochemical markers.

METHODS

Macroscopic analysis, normal histology, and immunohistochemical techniques for detecting neurofilaments (NF) and NOS1 were used to study ENS of 138 Sd mice and 25 controls.

RESULTS

The surprising results of this study showed that Sd mutation is associated with different degrees of hypoganglionosis and aganglionosis. In 41% of Sd/SD-affected mice, the rectal pouch was aganglionic and in the remaining 58% was severely hypoganglionic. In addition, 4.1% of heterozygous mice presented a distal aganglionosis and 8.3% hypoganglionosis.

CONCLUSIONS

These results suggest that Sd mutation independently affects distinct cell lines during early organogenesis, as notochord cells, ventral hingut endoderm, and neuroblasts migrating from neural crest cells. Comparing the Sd murine model with human pathology, this study confirms that the association between ARM and intestinal dysganglionosis is not rare and underlines the importance of detecting in every ARM patient the innervation abnormalities of rectal pouch and fistulas.

Genomic organization and chromosomal localization of the murine epididymal retinoic acid-binding protein (mE-RABP) gene

The murine epididymal retinoic acid-binding protein (mE-RABP) is specifically synthesized in the mouse mid/distal caput epididymidis and secreted in the lumen. In this report, we have demonstrated by Southern blot analysis of genomic DNA that mE-RABP is encoded by a single-copy gene. A mouse 129/SvJ genomic bacterial artificial chromosome (BAC) library was screened using a cDNA encoding the minor form of mE-RABP. One positive BAC clone was characterized and sequenced to determine the nucleotide sequence of the entire mE-RABP gene. The molecular cloning of the mE-RABP gene completes the characterization of the 20.5-kDa-predicted preprotein leading to the minor and major forms of mE-RABP. Comparison of the DNA sequence of the promoter and coding regions with that of the rat epididymal secretory protein I (ESP I) gene showed that the mE-RABP gene is the orthologue of the ESP I gene that encodes a rat epididymal retinoic acid-binding protein. Several regulatory elements, including a putative androgen receptor binding site, "CACCC-boxes," NF-1, Oct-1, and SP-1 recognition sites, are conserved in the proximal promoter. Analysis of the nucleotide sequence of the mE-RABP gene revealed the presence of seven exons and showed that the genomic organization is highly related to other genes encoding lipocalins. The mE-RABP gene was mapped by fluorescent in situ hybridization to the [A3-B] region of the murine chromosome 2. Our data, combined with that of others, suggest that the proximal segment of the mouse chromosome 2 may be a rich region for genes encoding lipocalins with a genomic organization highly related to the mE-RABP gene.

Brain spectrin: of mice and men

This article reviews our current knowledge of the structure of alpha spectrins and beta spectrins in the brain, as well as their location and expression within neural tissue. We discuss the known protein interactions of brain spectrin isoforms, and then describe results that suggest an important role for spectrin (alpha SpII sigma 1/beta SpII sigma 1) in the Ca(2+)-regulated release of neurotransmitters. Evidence that supports a role for spectrin in the docking of synaptic vesicles to the presynaptic plasma membrane and as a Ca2+ sensor protein that unclamps the fusion machinery is described, along with the Casting the Line model, which summarizes the information. We finish with a discussion of the value of spectrin and ankyrin-deficient mouse models in deciphering spectrin function in neural tissue.