A genome-wide association study with tissue transcriptomics identifies genetic drivers for classic bladder exstrophy.

Classic bladder exstrophy represents the most severe end of all human congenital anomalies of the kidney and urinary tract and is associated with bladder cancer susceptibility. Previous genetic studies identified one locus to be involved in classic bladder exstrophy, but were limited to a restrict number of cohort. Here we show the largest classic bladder exstrophy genome-wide association analysis to date where we identify eight genome-wide significant loci, seven of which are novel. In these regions reside ten coding and four non-coding genes. Among the coding genes is EFNA1, strongly expressed in mouse embryonic genital tubercle, urethra, and primitive bladder. Re-sequence of EFNA1 in the investigated classic bladder exstrophy cohort of our study displays an enrichment of rare protein altering variants. We show that all coding genes are expressed and/or significantly regulated in both mouse and human embryonic developmental bladder stages. Furthermore, nine of the coding genes residing in the regions of genome-wide significance are differentially expressed in bladder cancers. Our data suggest genetic drivers for classic bladder exstrophy, as well as a possible role for these drivers to relevant bladder cancer susceptibility.

Acute urinary retention in children.

BACKGROUND: Acute urinary retention is a common emergency in adult patients, foremost in older men. In childhood urinary retention is a rare entity with only sparse literature on the etiology. OBJECTIVE: To assess the etiology and treatment of acute urinary retention in the pediatric population and assess age and sex distribution. STUDY DESIGN: A retrospective analysis of all patients admitted to our emergency department with acute urinary retention between 2005 and 2019 was performed. Exclusion criteria were newborns (because of physiologic postnatal oliguria) and postoperative urinary retention during the same hospital stay. RESULTS: 113 children with acute urinary retention (ICD: R33) meeting the above criteria were identified. 16 Patients were excluded because of incomplete medical charts. 97 children were included into the study (age 0.5-18.3 years, mean age 5.3 years). 89 patients had one episode, 8 patients two episodes. A peak around the third year of age was observed. Sex ratio showed a 2:1 male to female distribution. Most common etiology was balanoposthitis (15.5%) and acute constipation/fecal impaction (15.5%). Traumatic urinary retention was found in 11.4% of the cases. Urinary tract infection were found 7.2%. No underlying reason could be found in 12.4% (idiopathic urinary retention). Other causes included febrile non-urinary infection (8.2%), subvesical obstruction (4.1%), vulvovaginitis (3.1%) and urethritis (2.1%). In 50% of the cases of urinary retention under 1 year of age (2 out of 4) an underlying tumor (rhabdomyosarcoma, sacral teratoma) was identified. DISCUSSION: Age and sex distribution were similar to previously published series; however, this study shows a marked difference concerning the etiology: e. g. we identified a significantly higher proportion of functional disorders as a reason for acute urinary retention in childhood. It is hypothesized that this is partly because previously published studies originate from areas (USA, Israel, Iran) with different socio-demographic and cultural background. CONCLUSION: AUR in children is a rare condition with very heterogeneous causes. Although the majority of cases exhibit mild underlying conditions, serious reasons, such as malignant diseases especially in the first year of life, must be excluded. AUR relief without catheterization is a child-friendly approach in cases of mild inflammatory or functional disorders and can help to minimize traumatization.

SLC20A1 Is Involved in Urinary Tract and Urorectal Development.

Previous studies in developing Xenopus and zebrafish reported that the phosphate transporter slc20a1a is expressed in pronephric kidneys. The recent identification of SLC20A1 as a monoallelic candidate gene for cloacal exstrophy further suggests its involvement in the urinary tract and urorectal development. However, little is known of the functional role of SLC20A1 in urinary tract development. Here, we investigated this using morpholino oligonucleotide knockdown of the zebrafish ortholog slc20a1a. This caused kidney cysts and malformations of the cloaca. Moreover, in morphants we demonstrated dysfunctional voiding and hindgut opening defects mimicking imperforate anus in human cloacal exstrophy. Furthermore, we performed immunohistochemistry of an unaffected 6-week-old human embryo and detected SLC20A1 in the urinary tract and the abdominal midline, structures implicated in the pathogenesis of cloacal exstrophy. Additionally, we resequenced SLC20A1 in 690 individuals with bladder exstrophy-epispadias complex (BEEC) including 84 individuals with cloacal exstrophy. We identified two additional monoallelic de novo variants. One was identified in a case-parent trio with classic bladder exstrophy, and one additional novel de novo variant was detected in an affected mother who transmitted this variant to her affected son. To study the potential cellular impact of SLC20A1 variants, we expressed them in HEK293 cells. Here, phosphate transport was not compromised, suggesting that it is not a disease mechanism. However, there was a tendency for lower levels of cleaved caspase-3, perhaps implicating apoptosis pathways in the disease. Our results suggest SLC20A1 is involved in urinary tract and urorectal development and implicate SLC20A1 as a disease-gene for BEEC.

Treatment Strategies and Outcome of the Exstrophy-Epispadias Complex in Germany: Data From the German CURE-Net.

Introduction: To evaluate the impact of reconstructive strategies and post-operative management on short- and long-term surgical outcome and complications of classical bladder exstrophy (CBE) patients' comprehensive data of the multicenter German-wide Network for Congenital Uro-Rectal malformations (CURE-Net) were analyzed. Methods: Descriptive analyses were performed between 34 prospectively collected CBE patients born since 2009, median 3 months old [interquartile range (IQR), 2-4 months], and 113 cross-sectional patients, median 12 years old (IQR, 6-21 years). Results: The majority of included individuals were males (67%). Sixty-eight percent of the prospectively observed and 53% of the cross-sectional patients were reconstructed using a staged approach (p = 0.17). Although prospectively observed patients were operated on at a younger age, the post-operative management did not significantly change in the years before and after 2009. Solely, in prospectively observed patients, peridural catheters were used significantly more often (p = 0.017). Blood transfusions were significantly more frequent in males (p = 0.002). Only half of all CBE individuals underwent inguinal hernia repair. Cross-sectional patients after single-stage reconstructions showed more direct post-operative complications such as upper urinary tract dilatations (p = 0.0021) or urinary tract infections (p = 0.023), but not more frequent renal function impairment compared to patients after the staged approach (p = 0.42). Continence outcomes were not significantly different between the concepts (p = 0.51). Self-reported continence data showed that the majority of the included CBE patients was intermittent or continuous incontinent. Furthermore, subsequent consecutive augmentations and catheterizable stomata did not significantly differ between the two operative approaches. Urinary diversions were only reported after the staged concept. Conclusions: In this German multicenter study, a trend toward the staged concept was observed. While single-stage approaches tended to have initially more complications such as renal dilatation or urinary tract infections, additional surgery such as augmentations and stomata appeared to be similar after staged and single-stage reconstructions in the long term.

Postoperative pain in small-for-gestational age infants after hernia repair, orchidopexy and urethral reconstruction surgery: A pilot study.

BACKGROUND: Small-for-gestational-age (SGA) birth bears an enhanced risk of developing hypertension, obesity, insulin resistance and mental health disorders in later life as a consequence of adaptive processes in utero. Only a small number of studies on pain perception in SGA infants exist. These are indicative of a blunted stress response to pain in SGA newborns. AIM: We initiated a pilot study investigating differences in postoperative pain perception between SGA and appropriate-for-gestational-age (AGA) infants. METHODS: Pain and alertness levels of 10 formerly SGA and 14 AGA infants at the age 0.5-2 years were evaluated by the FLACC scale, Steward and Aldrete Scores following hernia repair, reconstructive surgery of hypospadia and orchidopexy. In addition, the postoperative consumption of non-steroidal anti-inflammatory drugs was compared between SGA and AGA. RESULTS: Postoperative pain and alertness levels were not significantly different in SGA and AGA children. We did not observe significant group differences regarding the consumption of non-steroidal anti-inflammatory drugs. CONCLUSION: While previous studies were suggestive of a suppressed stress response to pain in SGA newborns, these findings did not fully translate into an altered response to pain beyond the newborn age. Further studies in a larger cohort seem necessary to verify this finding.

Association Between Exstrophy-epispadias Complex And Congenital Anomalies: A German Multicenter Study.

OBJECTIVE: To further investigate associated anomalies in exstrophy-epispadias complex (EEC) patients congenital uro-rectal malformations network (CURE-Net) database was systematically screened. In literature the EEC comprises a spectrum of anomalies, mainly occurring "isolated" without additional congenital defects. Nevertheless, previous epidemiological studies indicated a higher association with renal, anorectal, and lower neurotubular anomalies, which may originate from the same developmental morphogenetic fields. MATERIALS AND METHODS: Seventy-three prospectively (born since 2009) and 162 cross-sectional recruited EEC patients (born 1948-2008) were analyzed. Associated anomalies were derived from patient's medical data as well as from a physical examination during a physician's interview, classified according to the international statistical classification of diseases and related health problems and grouped with the London Dysmorphology Database. Descriptive statistical analyses were performed. RESULTS: Majority of participants were male (68%) and expressed the classical bladder exstrophy phenotype (71%). Exstrophy variants occurred significantly more often in newborns (21%, P < .0001). Anomalies such as inguinal hernias, skeleton, and joint anomalies were equally present in both groups (P = .65 and P = .67). Heart defects were seen more often in newborns (6%) than in the cross-sectional group (1%; P = .033) and the general German population (1%). In total, 59% of the prospective and 48% of the cross-sectional patients had associated anomalies outside the spectrum (P = .16). CONCLUSION: Phenomenological multicenter data confirmed the dimension of associated anomalies inside and outside the EEC spectrum. The detected anomalies are either important in preparing for the primary reconstruction or later in long-term follow-up. Associated anomalies of EEC should be spotlighted during routine check-up in all EEC patients.

Short-term adverse effects of testosterone used for priming in prepubertal boys before growth hormone stimulation test.

BACKGROUND: Despite the fact that priming with sex steroids in prepubertal children before growth hormone (GH) provocative tests is recommended, there is an ongoing controversial discussion about the appropriate age of the children, the drug used for priming, the dose and the period between priming and the GH test. Interestingly, there is no discussion on the safety of this procedure. To date, only little data have been available on the possible side effects of priming with testosterone. METHODS: We analyzed the outcome in 188 short-statured prepubertal boys who had been primed with testosterone enanthate (n=136: 50 mg; n=51: 125 mg, and accidentally one boy with 250 mg) 7 days prior to the GH test. Serum testosterone levels were measured on the day of the GH test in 99 boys. RESULTS: Overall, only five boys developed adverse side effects. Two boys (dose 125 mg) showed severe low-flow priapism and had to undergo decompression of the corpora cavernosa. One boy suffered from self-limiting priapism and testicular pain (dose 50 mg). Two patients reported testicular pain (each dose 50 mg). The single patient with 250 mg testosterone did not show any adverse effects. The total side effect rate was 2.7%. The serum testosterone levels of the boys with side effects were not different from the testosterone levels of the boys without any side effects. CONCLUSIONS: Parents and patients should be informed about the possible side effects of priming with testosterone such as priapism and testicular pain. However, the overall side effect rate is low. We found no correlation between the outcome and the testosterone dose used and/or the level of serum testosterone.

Sexual Function and Quality of Life in Adult Male Individuals with Exstrophy-Epispadias Complex-a Survey of the German CURE-Network.

OBJECTIVE: To investigate sexual function and quality of life (QoL) in adult male individuals with exstrophy-epispadias complex (EEC). Data from the German Network for Congenital Urorectal Malformations (CURE-Net) were used. PATIENTS AND METHODS: Fifty-one male participants (≥18 years) recruited by CURE-Net between 2009 and 2012 were re-contacted per mail and asked to fill out 4 questionnaires including International Index of Erectile Function (IIEF-5), Cologne Assessment of Erectile Dysfunction (KEED), the Short-Form 36 (SF-36), and one self-designed questionnaire about their medical history, current health status, and sexual experience. The SF-36 results were compared with general German population. RESULTS: Nineteen male participants (37%) completed all questionnaires (median age 26 years, 84% classical bladder exstrophy). The majority (68%) was reconstructed in a staged or single-staged approach; further 32% had a primary urinary diversion. Seventy-four percent of the participants reported a certain degree of urinary incontinence. Mean IIEF-15 results showed mild to moderate or moderate impairment in all domains. The SF-36 results revealed no difference in the German population. Subgroup analysis showed statistically significant lower results in certain SF-36 domains with regard to incontinence, dissatisfaction with genital appearance, and antihypertensive drug intake. CONCLUSION: Although there is no difference in overall QoL comparing male individuals with EEC to the general German population, incontinence, dissatisfaction with genital appearance, and taking antihypertensive medication seem to have a considerable impact on QoL. Furthermore, mild to moderate erectile dysfunction and moderate intercourse satisfaction were confirmed, suggesting the need for further improvement in care for adult male individuals with EEC.

[Diagnosis and Therapeutic Management in Kidney, Ureter and Bladder Trauma]. / Diagnose und Therapiemanagement bei Nieren-, Harnleiter- und Blasentrauma.

Trauma refers to the destruction of tissues or organs by external forces and it is the most common cause of mortality and morbidity in children (1, 2). Injuries of the genitourinary tract may be the result of blunt (falls, sport injuries, motor vehicle accidents and sexual abuse) or penetrating (stab wounds, gun shots, falling onto sharp objects) injuries. The genitourinary tract is significantly injured in 2.9% of paediatric trauma patients 4.In the paediatric population, the kidney is the most affected organ in the genitourinary tract (>60% of all genitourinary tract injuries) 4. Blunt renal trauma is the most common type of injury representing 80-90% 4. The paediatric kidney is more susceptible due to less abdominal and retroperitoneal fat, weaker trunk and abdominal muscles and a lower position in the abdomen. Preexisting renal abnormalities such as UPJ obstruction, hydronephrosis, horseshoe kidney or ectopic kidney make the kidney more vulnerable. Spiral computed tomography is the gold standard method for radiological assessment. Surgical intervention is needed only in the minority of children. Isolated ureteral injury due to trauma is very rare in children. Penetrating ureteral trauma is more common than blunt trauma in the paediatric population. Among all urological trauma cases, the incidence of ureteral injury is lower than 1% [4]. Ureteral injuries include contusion, laceration and avulsion. Because of their hyperextensible vertebral column, children are more likely to sustain deceleration injuries. Delayed films of IVP and CT are the main diagnostic tools whereas the gold standard is retrograde ureteropyelography. Ureteral injury treatment options depend on the location of injury. The bladder in children is a more abdominal organ than in adults. Lying in an exposed position above the pelvis, the bladder is more vulnerable in this age group as it is less well protected due to the less developed abdominal fat and rectus muscles. Here, too, the most common type of trauma is blunt injury. High percentages of bladder injuries are associated with pelvic fractures (70-90%) 4. The average rate of bladder injury in patients with pelvic fractures is 4% in the paediatric age group 4. Conventional or CT cystography is the gold standard method of imaging.

Evaluation of sexual function in females with exstrophy-epispadias-complex: A survey of the multicenter German CURE-Net.

OBJECTIVE: Standardized knowledge about genital function in adult female individuals with exstrophy-epispadias complex (EEC) is scarce. The aim of this study was to investigate sexual function using the standardized Female Sexual Function Index (FSFI), and to assess the influence of bladder and vaginal reconstruction and the presence of incontinence on FSFI results. METHOD: Sixty-one females (aged ≥18 years) recruited by the German multicenter network for congenital uro-rectal malformations (CURE-Net) were asked to complete the FSFI and a self-designed semi-structured questionnaire assessing comprehensive medical data, gynecological, and psychosocial items. Twenty-one eligible females (34%) returned both questionnaires (mean ± standard deviation [SD] age of 26 ± 5.1 years). RESULTS: In 43% of participants, a staged or single-staged approach had been used for reconstruction, and these had their bladder in use. A primary or secondary urinary diversion (UD) after cystectomy had been performed in 38% of participants. Of the participants, 57% lived in a committed partnership, and 62% had sexual intercourse on a regular basis, with a further 19% experiencing pain or discomfort thereby. Introitus plasty was done in 43%. Mean total FSFI for all participants was 21.3 (SD 1.9). Most domain scores of patients after introitus plasty were similar compared with those without an operative vaginal approach, except for satisfaction (p = 0.057) and pain (p = 0.024). Comparing incontinent with continent patients, significant differences were found for desire (mean 4.6 vs. 3.5, p = 0.021), lubrication (mean 3.1 vs. 4.2, p = 0.049), and satisfaction (mean 1.6 vs. 3.6, p = 0.0065). In contrast pain was not significant between groups. CONCLUSIONS: Sexual activity rate in the present study was similar to that reported in the literature (81% vs. 89%), whereas dyspareunia rate was lower in our cohort (19% vs. 24%). The risk for sexual dysfunction seems to be lower in patients reconstructed with primary or secondary UD than patients with bladder in use. It is surprising that lubrification was better after UD than after bladder neck surgery. Incontinence and in some parts the history of an introitus plasty may play an additional role in development of sexual dysfunction in EEC. Although most of the female EEC patients lived in a committed partnership and had sexual intercourse, total FSFI values <26.55 clearly indicate a risk of sexual dysfunction. Although continence itself played a major role, females reconstructed with UD seem to have better sexual function. Further evaluation of sexual outcome and improvement of care for these patients is mandatory.

CNV analysis in 169 patients with bladder exstrophy-epispadias complex.

BACKGROUND: The bladder exstrophy-epispadias complex (BEEC) represents the severe end of the congenital uro-rectal malformation spectrum. Initial studies have implicated rare copy number variations (CNVs), including recurrent duplications of chromosomal region 22q11.21, in BEEC etiology. METHODS: To detect further CNVs, array analysis was performed in 169 BEEC patients. Prior to inclusion, 22q11.21 duplications were excluded using multiplex ligation-dependent probe amplification. RESULTS: Following the application of stringent filter criteria, seven rare CNVs were identified: n = 4, not present in 1307 in-house controls; n = 3, frequency of <0.002 in controls. These CNVs ranged from 1 to 6.08 Mb in size. To identify smaller CNVs, relaxed filter criteria used in the detection of previously reported BEEC associated chromosomal regions were applied. This resulted in the identification of six additional rare CNVs: n = 4, not present in 1307 in-house controls; n = 2, frequency <0.0008 in controls. These CNVs ranged from 0.03-0.08 Mb in size. For 10 of these 13 CNVs, confirmation and segregation analyses were performed (5 of maternal origin; 5 of paternal origin). Interestingly, one female with classic bladder extrophy carried a 1.18 Mb duplication of 22q11.1, a chromosomal region that is associated with cat eye syndrome. CONCLUSIONS: A number of rare CNVs were identified in BEEC patients, and these represent candidates for further evaluation. Rare inherited CNVs may constitute modifiers of, or contributors to, multifactorial BEEC phenotypes.

Genome-wide association study and meta-analysis identify ISL1 as genome-wide significant susceptibility gene for bladder exstrophy.

The bladder exstrophy-epispadias complex (BEEC) represents the severe end of the uro-rectal malformation spectrum, and is thought to result from aberrant embryonic morphogenesis of the cloacal membrane and the urorectal septum. The most common form of BEEC is isolated classic bladder exstrophy (CBE). To identify susceptibility loci for CBE, we performed a genome-wide association study (GWAS) of 110 CBE patients and 1,177 controls of European origin. Here, an association was found with a region of approximately 220kb on chromosome 5q11.1. This region harbors the ISL1 (ISL LIM homeobox 1) gene. Multiple markers in this region showed evidence for association with CBE, including 84 markers with genome-wide significance. We then performed a meta-analysis using data from a previous GWAS by our group of 98 CBE patients and 526 controls of European origin. This meta-analysis also implicated the 5q11.1 locus in CBE risk. A total of 138 markers at this locus reached genome-wide significance in the meta-analysis, and the most significant marker (rs9291768) achieved a P value of 2.13 × 10-12. No other locus in the meta-analysis achieved genome-wide significance. We then performed murine expression analyses to follow up this finding. Here, Isl1 expression was detected in the genital region within the critical time frame for human CBE development. Genital regions with Isl1 expression included the peri-cloacal mesenchyme and the urorectal septum. The present study identified the first genome-wide significant locus for CBE at chromosomal region 5q11.1, and provides strong evidence for the hypothesis that ISL1 is the responsible candidate gene in this region.

Genome-wide association study and mouse expression data identify a highly conserved 32 kb intergenic region between WNT3 and WNT9b as possible susceptibility locus for isolated classic exstrophy of the bladder.

Bladder exstrophy-epispadias complex (BEEC), the severe end of the urorectal malformation spectrum, has a profound impact on continence as well as sexual and renal functions. It is widely accepted that for the majority of cases the genetic basis appears to be multifactorial. Here, we report the first study which utilizes genome-wide association methods to analyze a cohort comprising patients presenting the most common BEEC form, classic bladder exstrophy (CBE), to identify common variation associated with risk for isolated CBE. We employed discovery and follow-up samples comprising 218 cases/865 controls and 78 trios in total, all of European descent. Our discovery sample identified a marker near SALL1, showing genome-wide significant association with CBE. However, analyses performed on follow-up samples did not add further support to these findings. We were also able to identify an association with CBE across our study samples (discovery: P = 8.88 × 10(-5); follow-up: P = 0.0025; combined: 1.09 × 10(-6)) in a highly conserved 32 kb intergenic region containing regulatory elements between WNT3 and WNT9B. Subsequent analyses in mice revealed expression for both genes in the genital region during stages relevant to the development of CBE in humans. Unfortunately, we were not able to replicate the suggestive signal for WNT3 and WNT9B in a sample that was enriched for non-CBE BEEC cases (P = 0.51). Our suggestive findings support the hypothesis that larger samples are warranted to identify association of common variation with CBE.

Assisted reproductive techniques and risk of exstrophy-epispadias complex: a German case-control study.

PURPOSE: We assessed the risk of exstrophy-epispadias complex in children conceived by in vitro fertilization or intracytoplasmic sperm injection. MATERIALS AND METHODS: Data from the German Network for Congenital Uro-REctal malformations were compared to nationwide data from the German In Vitro Fertilization Register and the German Federal Statistical Office. Odds ratios (95% CI) were determined to quantify associations using logistic regression. RESULTS: A total of 123 patients with exstrophy-epispadias complex born in Germany between 1997 and 2011 were recruited through participating departments of pediatric urology and pediatric surgery throughout the country as well as the German self-help organizations Blasenekstrophie/Epispadie e.V. and Kloakenekstrophie. All German live births (10,069,986) between 1997 and 2010 comprised the controls. Overall, 12 subjects (10%) and 129,982 controls (1%) were conceived by in vitro fertilization or intracytoplasmic sperm injection. Conception by assisted reproductive technique was associated with a more than eightfold increased risk of exstrophy-epispadias complex compared to spontaneous conception (OR 8.3, 95% CI 4.6-15.0, p <0.001). Separate analyses showed a significantly increased risk of exstrophy-epispadias complex in children conceived by in vitro fertilization (OR 14.0, 95% CI 6.5-30.0, p <0.0001) or intracytoplasmic sperm injection (OR 5.3, 95% CI 2.2-12.9, p <0.0001). CONCLUSIONS: This study provides evidence that assisted reproductive techniques such as in vitro fertilization and intracytoplasmic sperm injection are associated with a markedly increased risk of having a child born with exstrophy-epispadias complex. However, it remains unclear whether this finding may be due to assisted reproduction per se and/or underlying infertility/subfertility etiology or parent characteristics.

Umbilical rotation: a new technique for the cutaneous fixation of continent catheterizable vesicostomies.

PURPOSE: For cutaneous fixation of the continent catheterizable vesicostomy we present a new technique, in which the umbilicus is rotated caudally by 180° and the catheterizable channel is sutured to the umbilical cone. This procedure reduces the distance between the stoma entrance and the bladder. MATERIALS AND METHODS: Between 2001 and 2008, 67 patients underwent construction of a continent catheterizable vesicostomy. In 82% (n = 55), this was an appendicovesicostomy according to the Mitrofanoff principle. For 21 of these patients, later in the series (2005 onwards), the procedure involved rotation of the umbilicus. We evaluated cosmetic outcome and channel-related complication rates and compared the results between the two groups, with and without umbilical rotation. RESULTS: The overall complication rate was 22.4% (n = 15); stoma stenosis occurred in eight cases. In the majority of cases with complications, endoscopic treatment was sufficient. The complication rate was significantly lower in the group with umbilical rotation compared to the other group (14.3% vs 26.1%, P < 0.02). CONCLUSIONS: Umbilical rotation always enables cutaneous implantation of the vesicostomy in the umbilical pit and is a safe and straightforward procedure.

Cdc42-dependent leading edge coordination is essential for interstitial dendritic cell migration.

Mature dendritic cells (DCs) moving from the skin to the lymph node are a prototypic example of rapidly migrating amoeboid leukocytes. Interstitial DC migration is directionally guided by chemokines, but independent of specific adhesive interactions with the tissue as well as pericellular proteolysis. Instead, the protrusive flow of the actin cytoskeleton directly drives a basal mode of locomotion that is occasionally supported by actomyosin contractions at the trailing edge to propel the cell's rigid nucleus. We here delete the small GTPase Cdc42 in DCs and find that actin flow and actomyosin contraction are still initiated in response to chemotactic cues. Accordingly, the cells are able to polarize and form protrusions. However, in the absence of Cdc42 the protrusions are temporally and spatially dysregulated, which leads to impaired leading edge coordination. Although this defect still allows the cells to move on 2-dimensional surfaces, their in vivo motility is completely abrogated. We show that this difference is entirely caused by the geometric complexity of the environment, as multiple competing protrusions lead to instantaneous entanglement within 3-dimensional extracellular matrix scaffolds. This demonstrates that the decisive factor for migrating DCs is not specific interaction with the extracellular environment, but adequate coordination of cytoskeletal flow.

Rapid leukocyte migration by integrin-independent flowing and squeezing.

All metazoan cells carry transmembrane receptors of the integrin family, which couple the contractile force of the actomyosin cytoskeleton to the extracellular environment. In agreement with this principle, rapidly migrating leukocytes use integrin-mediated adhesion when moving over two-dimensional surfaces. As migration on two-dimensional substrates naturally overemphasizes the role of adhesion, the contribution of integrins during three-dimensional movement of leukocytes within tissues has remained controversial. We studied the interplay between adhesive, contractile and protrusive forces during interstitial leukocyte chemotaxis in vivo and in vitro. We ablated all integrin heterodimers from murine leukocytes, and show here that functional integrins do not contribute to migration in three-dimensional environments. Instead, these cells migrate by the sole force of actin-network expansion, which promotes protrusive flowing of the leading edge. Myosin II-dependent contraction is only required on passage through narrow gaps, where a squeezing contraction of the trailing edge propels the rigid nucleus.