What could health technology assessment learn from living clinical practice guidelines?

A "living" approach to clinical practice guidelines is when the identification, appraisal and synthesis of evidence is maintained and repeated at an agreed frequency, with a clear process for when and how new evidence is to be incorporated. The value of a living approach to guidelines was emphasised during the COVID-19 pandemic when health professionals and policymakers needed to make decisions regarding patient care in the context of a nascent but rapidly evolving evidence base. In this perspective, we draw on our recent experience developing Australian and international living guidelines and reflect on the feasibility of applying living guideline methods and processes to a lifecycle approach to health technology assessment (HTA). We believe the opportunities and challenges of adopting a living approach in HTA fall into five key themes: identification, appraisal and synthesis of evidence; optimising the frequency of updates; embedding ongoing multi-stakeholder engagement; linking the emergence of new evidence to reimbursement; and system capacity to support a living approach. We acknowledge that the suitability of specific living approaches to HTA will be heavily influenced by the type of health technology, its intended use in the health system, local reimbursement pathways, and other policy settings. But we believe that the methods and processes applied successfully to guideline development to manage evidentiary uncertainty could be applied in the context of HTA and reimbursement decision-making to help manage similar sources of uncertainty.

A Retrospective Case Control Study Examining Procalcitonin as a Biomarker for Necrotizing Enterocolitis.

Background: Procalcitonin (PCT) is a biomarker for sepsis, but its utility has not been investigated in necrotizing enterocolitis (NEC). Necrotizing enterocolitis is a devastating multisystem disease of infants that in severe cases requires surgical intervention. We hypothesize that an elevated PCT will be associated with surgical NEC. Patients and Methods: After obtaining Institutional Review Board (IRB) approval (#12655), we performed a single institution retrospective case control study between 2010 and 2021 of infants up to three months of age. Inclusion criteria was PCT drawn within 72 hours of NEC or sepsis diagnosis. Control infants had a PCT drawn in the absence of infectious symptoms. Recursive partitioning (RP) identified PCT cutoffs. Categorical variable associations were tested using Fisher exact or χ2 tests. Continuous variables were tested using Wilcoxon rank sum test, Student t-test, and Kruskal-Wallis test. Adjusted associations of PCT and other covariables with NEC or sepsis versus controls were obtained via multinomial logistic regression analysis. Results: We identified 49 patients with NEC, 71 with sepsis, and 523 control patients. Based on RP, we selected two PCT cutoffs: 1.4 ng/mL and 3.19 ng/ml. A PCT of ≥1.4 ng/mL was associated with surgical (n = 16) compared with medical (n = 33) NEC (87.5% vs. 39.4%; p = 0.0015). A PCT of ≥1.4 ng/mL was associated with NEC versus control (p < 0.0001) even when adjusting for prematurity and excluding stage IA/IB NEC (odds ratio [OR], 28.46; 95% confidence interval [CI], 11.27-71.88). A PCT of 1.4-3.19 ng/mL was associated with both NEC (adjusted odds ratio [aOR], 11.43; 95% CI, 2.57-50.78) and sepsis (aOR, 6.63; 95% CI, 2.66-16.55) compared with controls. Conclusions: A PCT of ≥1.4 ng/mL is associated with surgical NEC and may be a potential indicator for risk of disease progression.

No prostate? No problem: robotic inguinal hernia repair after prostatectomy.

Traditional teaching suggests that prior pelvic operations, including prostatectomy, are a contraindication to laparoscopic inguinal hernia repair. Despite the growing use of robotic platforms in inguinal hernia repair, there are few studies describing robotic-assisted inguinal hernia repairs (RIHR) in this patient population. This study aims to demonstrate that RIHR is safe and effective in repairing inguinal hernias in patients who had previously undergone prostatectomy. We retrospectively reviewed RIHR cases performed from March 2017 to October 2021 by a single surgeon at our university-affiliated community hospital. Cases were reviewed for preoperative considerations, operative times and complications, and postoperative outcomes. A total of 30 patients with prior prostatectomy underwent transabdominal preperitoneal (TAPP) RIHR with mesh. Sixteen of the 30 patients had undergone robot-assisted laparoscopic prostatectomy (RALP), while 14 patients underwent open resection. Seven of the patients had received post-resection radiation and 12 had previous non-urologic abdominal operations. When compared to all RIHRs performed over the same period, duration of surgery was increased. There were no conversions to open surgery. Postoperatively, one patient developed a repair site seroma which resolved after 1 month. Mean follow-up time was 8.0 months. At follow-up, one patient reported experiencing intermittent non-debilitating pain at the repair site and one patient developed an inguinoscrotal abscess of unknown relation to the repair. No patients reported hernia recurrences nor mesh infection. This review suggests that TAPP RIHR can be a safe and effective approach to inguinal hernia repair in patients who have previously undergone prostatectomy, including those who received radiation and those who underwent either open or robotic resections.

G-CSF Is a Novel Mediator of T-Cell Suppression and an Immunotherapeutic Target for Women with Colon Cancer.

PURPOSE: G-CSF enhances colon cancer development. This study defines the prevalence and effects of increased G-CSF signaling in human colon cancers and investigates G-CSF inhibition as an immunotherapeutic strategy against metastatic colon cancer. EXPERIMENTAL DESIGN: Patient samples were used to evaluate G-CSF and G-CSF receptor (G-CSFR) levels by IHC with sera used to measure G-CSF levels. Peripheral blood mononuclear cells were used to assess the rate of G-CSFR+ T cells and IFNγ responses to chronic ex vivo G-CSF. An immunocompetent mouse model of peritoneal metastasis (MC38 cells in C57Bl/6J) was used to determine the effects of G-CSF inhibition (αG-CSF) on survival and the tumor microenvironment (TME) with flow and mass cytometry. RESULTS: In human colon cancer samples, the levels of G-CSF and G-CSFR are higher compared to normal colon tissues from the same patient. High patient serum G-CSF is associated with increases in markers of poor prognosis, (e.g., VEGF, IL6). Circulating T cells from patients express G-CSFR at double the rate of T cells from controls. Prolonged G-CSF exposure decreases T cell IFNγ production. Treatment with αG-CSF shifts both the adaptive and innate compartments of the TME and increases survival (HR, 0.46; P = 0.0237) and tumor T-cell infiltration, activity, and IFNγ response with greater effects in female mice. There is a negative correlation between serum G-CSF levels and tumor-infiltrating T cells in patient samples from women. CONCLUSIONS: These findings support G-CSF as an immunotherapeutic target against colon cancer with greater potential benefit in women.

Association of Age and Overall Survival in Surgically Resected Colorectal Cancer Patients.

INTRODUCTION: Incidence of colorectal cancer (CRC) among young patients has increased in the last 20 y often with more aggressive tumor biology. It is unclear if age < 50 y is an independent factor for shorter overall survival in CRC patients. Our objective was to determine if younger age at diagnosis was associated with worse overall survival. METHODS: This study used the National Cancer Data Base (2004-2016), retrospectively reviewing patients who underwent surgical resection for CRC. Patients were limited to only those without comorbidities and primary outcome was overall survival for all patients. RESULTS: Older patients have worse overall survival as compared to younger patients at a lower stage of disease (I and II) after adjusting for tumor location, gender, histology, stage, and systemic chemotherapy (< 36 y old versus 36-55 y old hazard ratio [HR] 1.16, confidence interval [CI] 1.03-1.29). This survival benefit is eliminated at a higher stage of disease, stage III in 36-55 y old versus < 36 y old (HR 0.96 [CI 0.90-1.03.99]) and stage IV (HR 0.94 [CI 0.89-0.99]). CONCLUSIONS: Older patients (aged > 36 y) have worse overall survival at a lower stage of disease, but the survival among all age groups was similar for stage III or IV disease in CRC.

Retrospective Cohort Analysis of the Effect of Age on Lymph Node Harvest, Positivity, and Ratio in Colorectal Cancer.

Introduction: Colon cancer among young patients has increased in incidence and mortality over the past decade. Our objective was to determine if age-related differences exist for total positive nodes (TPN), total lymph node harvest (TLH), and lymph node ratio (LNR). Material and Methods: A retrospective review of stage III surgically resected colorectal cancer patient data in the National Cancer Database (2004−2016) was performed, reviewing TPN, TLH, and LNR (TPN/TLH). Results: Unadjusted analyses suggested significantly higher levels of TLH and TPN (p < 0.0001) in younger patients, while LNR did not differ by age group. On adjusted analysis, TLH remained higher in younger patients (<35 years 1.56 (CI 95 1.54, 1.59)). The age-related effect was less pronounced for LNR (<35 years 1.16 (CI 95 1.13, 1.2)). Conclusion: Younger patients have increased TLH, even after adjusting for known confounders, while age does not have a strong independent impact on LNR.

Retrospective review of intervention for traumatic blunt spleen injuries in adolescents by trauma center type.

BACKGROUND: Management guidelines for pediatric blunt spleen injuries (BSI) include adolescent patients but few studies have compared current management of adolescents with respect to other age groups by center type. METHODS: A retrospective review of 2017-2018 National Trauma Quality Improvement (TQIP) data of children (6-12), adolescents (13-17) and young adults (18-24) with BSI presenting to an adult, pediatric only, or adult/pediatric trauma center, comparing the rate of splenic intervention for adolescents by trauma center was performed. RESULTS: Children had lower odds of spleen intervention than adolescents at both adult (OR 0.61 95%CI 0.39, 0.95) and adult/pediatric (OR 0.55 95%CI 0.35, 0.87) centers but did not differ at pediatric centers (OR 0.94 95%CI 0.39, 2.2) (n = 10,494). Adolescents adjusted odds of intervention was equal to adults at adult trauma centers (OR 1.2 95%CI 0.95, 1.4). CONCLUSION: Adolescents are more likely to undergo interventions for BSI as compared to children at both adult and adult/pediatric trauma centers.

Traumatic Pediatric Fatalities: Are They Preventable?

INTRODUCTION: Trauma related injury remains the leading cause of mortality in pediatric patients, many of which are preventable. The goal of our study was to identify the mechanism of injury (MOI) in pediatric trauma-related fatalities and determine if these injuries were preventable to direct future injury prevention efforts within trauma programs. METHODS: After IRB approval, a retrospective, single-institution review of pediatric (age ≤18) trauma fatalities from 2010 to 2019 was performed. MOI, use of protective devices, demographics, and whether the injury was preventable were collected. Patients were divided into five age cohorts, and frequencies and proportions were used to summarize data. Bivariate testing was done using Fisher's exact and Monte Carlo estimates for the exact test. RESULTS: MOI was found to vary by age with non-accidental trauma found to be the most common cause of trauma related deaths in children <1 (88.5%) and 1-4 (33.3%). MVC was the most common MOI in children >5 y, with 68.4% in the 5-9, 34.4% in the 10-14, and 45.8% in the 15-18 age group. The majority of fatalities resulted from a preventable injury (P < 0.0001) in the younger children with a negative association as age increased: 92.3% <1, 53.3% in 1-4, 36.8% in 5-9, 46.9% in 10-14 and 48.6% in 15-18. Of the preventable injuries, non-accidental trauma was the most common MOI in children <5, while GSW was the most common MOI in children >10. CONCLUSIONS: This study demonstrates many pediatric fatalities are the result of a preventable traumatic injury. This data can guide focused traumatic injury prevention efforts.

This is Our Lane: A Pilot Study Examining the Surgeon's Role in Social Justice Advocacy.

BACKGROUND: Despite the importance of social justice advocacy, surgeon attitudes toward individual involvement vary. We hypothesized that the majority of surgeons in this study, regardless of gender or training level, believe that surgeons should be involved in social justice movements. METHODS: A survey was distributed to surgical faculty and trainees at three academic tertiary care centers. Participation was anonymous with 123 respondents. Chi-square and Fisher's exact test were used for analysis with significance accepted when p < 0.05. Thematic analysis was performed on free responses. RESULTS: The response rate was 46%. Compared to men, women were more likely to state that surgeons should be involved (86% vs 64%, p = 0.01) and were personally involved in social justice advocacy (86% vs 51%, p = 0.0002). Social justice issues reported as most important to surgeons differed significantly by gender (p = 0.008). Generated themes for why certain types of advocacy involvement were inappropriate were personal choices, professionalism and relationships. CONCLUSIONS: Social justice advocacy is important to most surgeons in this study, especially women. This emphasizes the need to incorporate advocacy into surgical practice.

Correlation of Supervised Independence and Performance with Procedure Difficulty amongst Surgical Residents Stratified by Post Graduate Year.

PURPOSE: This study investigates the role of procedure difficulty on attending ratings of supervised levels of independence and procedural performance amongst general surgery residents, while accounting for case complexity. METHODS: Attending ratings for residents were obtained from System for Improving and Measuring Procedural Learning (SIMPL) database. Current procedural terminology (CPT) codes were used to match procedures to a corresponding work relative value unit (wRVU) as a surrogate for procedure difficulty. Three categories of wRVU (<13.07, 13.07-22, >22) were identified using recursive partitioning. Procedures were also divided into 'Core' or 'Advanced' as defined by the American Board of Surgery Surgical Council on Resident Education (SCORE). Temporal advancement in resident skill was accounted for through academic quarterly analysis. A generalized estimating equations (GEE) approach was used to form separate multivariable logistic regression models for meaningful autonomy (MA) and satisfactory performance (SP) adjusted for potential clustering by program, subject, and rater. Models were further adjusted for core/advanced procedures, attending rated complexity, and academic quarter. RESULTS: A total of 33,281 ratings were analyzed. Overall, 51.6% were rated as MA and 44.4% as SP. For core procedures, surgical residents rated as MA (53.5%) and SP (45.7%), which was twice as high as those for advance procedures (MA-29.2%, SP-29.0%). MA and SP both decreased with increasing wRVU (Figure 2 &3). Using a wRVU<13.07 as a reference, the adjusted odds ratios of MA and SP were significantly lower with increasing procedure difficulty, 0.44 for wRVU 13.07-22.0 and 0.24 for wRVU >22.00 (Table 3). Post graduate year (PGY) 5 residents in the final quarter of training obtain MA in 95.5% and SP 92.9% for core procedures with wRVU <13.07 (Table 4). CONCLUSION: Increasing procedural difficulty is independently associated with decreases in meaningful autonomy and satisfactory performance. As residents approach graduation the level of meaningful autonomy and satisfactory performance both reach high levels for common core procedures but decrease as procedural difficulty increases.

Pediatric Snakebites: Comparing Patients in Two Geographic Locations in the United States.

BACKGROUND: Management of children with snakebites may vary based on subjective criteria, geographic, and climatic factors. We reviewed the incidence and management of snakebite injuries in children at two tertiary referral centers in separate geographic and climatic location to assess differences in management and outcomes of these patients. METHODS: After institutional review board approval, a retrospective chart review was performed for patients ≤18 years with snakebite injuries at emergency departments (ED) of two American College of Surgeons verified trauma centers (2006-2013). One center is in southeast US and experiences a sub-tropical climate whereas the other is in southwest US and experiences a semi-arid climate. Demographic and clinical parameters were extracted. RESULTS: A total of 108 patients (59% male), median age of 9 y (1 y-17 y), were included. Snake type was identified by bystanders in 55.5% cases; copperhead was the most common (37%) subtype. Approximately 30% of patients received antivenom. One quarter of all patients were discharged from the ED. Two patients received surgical intervention in the first 48 hours after presentation. Compared to patients who sustained a snakebite in semi-tropical regions, patients in semi-arid areas had shorter bite-to-ED time, presented directly to the referral center, were more frequently bitten by a rattlesnake, had longer lengths of hospital stay, required antivenom more frequently and at higher doses, and were more frequently admitted to the ICU. No differences were seen in gender, age at presentation, severity of wound, location of bite, abnormalities in coagulation profile or rate of admission to hospital amongst the two sites. CONCLUSIONS: Patients sustaining snakebites in semi-arid climates were more commonly exposed to dangerous snake types, resulting in higher antivenom requirement, as well as longer hospital stays and need for intensive monitoring. Although no fatalities were reported in our study, our data supports early transfer of snakebite victims to higher levels of care, especially in semi-arid or high-risk areas.

Women survive longer than men undergoing cytoreductive surgery and HIPEC for appendiceal cancer.

BACKGROUND: We hypothesize that women undergoing cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) for peritoneal carcinomatosis from appendiceal cancer will have a survival advantage compared to men. METHODS: The National Cancer Database (NCDB) public user file (2004-2014) was used to select patients with PC undergoing CRS and HIPEC from appendiceal cancer. Univariate and multivariable analyses were performed. RESULTS: 1,190 patients with PC from appendiceal cancer underwent HIPEC and CRS. OS was significantly longer for women than for men, with mean and median OS being 73.8 months and 98.2 months for women vs 58.7 months and 82.5 months for men, respectively (p = 0.0032). On multivariable analysis, male sex (HR: 1.444, 95% CI: 1.141-1.827, p = 0.0022) and increasing age (HR: 1.017, 95% CI: 1.006-1.027, p = 0.0017) were both found to be independent risk factors for worse OS. CONCLUSION: Women undergoing CRS and HIPEC for PC from appendiceal origin live longer than men undergoing the same treatment. Increasing age was also found to be independent risk factors for worse survival.

Feasibility of robotic-assisted minimally invasive inguinal hernia repair in patients with urologic considerations including artificial urinary sphincters and bladder herniation.

Robotic surgical technology has the potential to broaden the applicability of minimally invasive approaches into more complex, technically challenging inguinal hernia repairs. A unique patient population requiring inguinal hernia repair are those patients who either have artificial urinary sphincters (AUS) or inguinal bladder herniation (IBH). Traditionally, these patients have not been considered candidates for minimally invasive inguinal hernia repairs. Through this retrospective series, we aim to contribute to the growing body of literature on robotic-assisted inguinal hernia repair (RIHR) by describing our experience with RIHR in this patient subset. We performed a retrospective chart review of RIHR cases performed from June 2017 to April 2019 by a single surgeon at our university-affiliated community hospital. Charts were reviewed for preoperative considerations, operative complications, and postoperative outcomes. A total of three patients with an AUS and six patients with IBH were included, all of whom were male. All the patients received transabdominal preperitoneal (TAPP) approaches, and all received placement of mesh. There were no intraoperative complications and no conversions to open surgery. Postoperatively, one patient with IBH had persistent surgical site pain that resolved after 3 weeks and one patient, also with IBH, had a surgical site seroma that resolved without further intervention. Mean follow-up time was 10.71 and 12.13 months for patients with AUS and IBH, respectively. No patients reported hernia recurrence during this time. This review suggests that the use of robotic assistance for laparoscopic inguinal hernia repair is safe and effective and may provide additional benefits for patients with concurrent urological considerations such as AUS and IBH.

Infant Essential Fatty Acid Status Is Not Associated With Postoperative Wound Complication Severity.

BACKGROUND: Neonates are susceptible to postoperative wound complications (POWCs), as prematurity, hypoxia, steroid use, immunosuppression, and malnutrition are all common comorbidities. Critically ill infants, dependent on parenteral nutrition, are at even further risk of developing essential fatty acid deficiency (EFAD). We hypothesized that POWC severity and EFAD were associated because of increased susceptibility to infections and impaired wound healing seen with EFAD. METHODS: Institutional review board-approved (OUHSC10554), retrospective review from our academic Level IV Neonatal Intensive Care Unit. Infants aged <1 y who underwent a fascial-compromising gastrointestinal surgery from June 1, 2015, to March 15, 2019, and who had essential fatty acids (EFAs) measured ±2 wk from surgery were included. Three blinded investigators independently categorized POWC using the World Union of Wound Healing Society Surgical Wound Grading System. Infants were categorized into three groups: no POWC, POWC Grades 1 and 2 (superficial tissue nonintegrity), and POWC Grades 3 and 4 (deep tissue nonintegrity and complete dehiscence). EFA status and other possible POWC-associated factors were analyzed to determine any association with wound severity. RESULTS: Fifty infants met the inclusion criteria. Half (25/50) had no POWC, 30% (15/50) had Grade 1 or 2, and 20% (10/50) had Grade 3 or 4. We found no association between EFAD and POWC severity. CONCLUSIONS: In our cohort, EFA status did not predict POWC severity. At this time, we cannot suggest delaying elective surgical procedures to correct EFAD as an approach to preventing POWC.

Context-specific function of the LIM homeobox 1 transcription factor in head formation of the mouse embryo.

Lhx1 encodes a LIM homeobox transcription factor that is expressed in the primitive streak, mesoderm and anterior mesendoderm of the mouse embryo. Using a conditional Lhx1 flox mutation and three different Cre deleters, we demonstrated that LHX1 is required in the anterior mesendoderm, but not in the mesoderm, for formation of the head. LHX1 enables the morphogenetic movement of cells that accompanies the formation of the anterior mesendoderm, in part through regulation of Pcdh7 expression. LHX1 also regulates, in the anterior mesendoderm, the transcription of genes encoding negative regulators of WNT signalling, such as Dkk1, Hesx1, Cer1 and Gsc. Embryos carrying mutations in Pcdh7, generated using CRISPR-Cas9 technology, and embryos without Lhx1 function specifically in the anterior mesendoderm displayed head defects that partially phenocopied the truncation defects of Lhx1-null mutants. Therefore, disruption of Lhx1-dependent movement of the anterior mesendoderm cells and failure to modulate WNT signalling both resulted in the truncation of head structures. Compound mutants of Lhx1, Dkk1 and Ctnnb1 show an enhanced head truncation phenotype, pointing to a functional link between LHX1 transcriptional activity and the regulation of WNT signalling. Collectively, these results provide comprehensive insight into the context-specific function of LHX1 in head formation: LHX1 enables the formation of the anterior mesendoderm that is instrumental for mediating the inductive interaction with the anterior neuroectoderm and LHX1 also regulates the expression of factors in the signalling cascade that modulate the level of WNT activity.

Regionalisation of the endoderm progenitors and morphogenesis of the gut portals of the mouse embryo.

This fate-mapping study reveals that the progenitors of all major parts of the embryonic gut are already present in endoderm of the early-head-fold to early-somite stage (1-9 somites) mouse embryo. The anterior endoderm contributes primarily to the anterior intestinal portal of the early-organogenesis stage (16-19 somites) embryo. Endoderm cells around and lateral to the node are allocated to the open "midgut" region of the embryonic gut. The posterior (post-nodal) endoderm contributes not only to the posterior intestinal portal but also the open "midgut". Descendants of the posterior endoderm span a length of the gut from the level of the 3rd-5th somites to the posterior end of the embryonic gut. The formation of the anterior and posterior intestinal portals is accompanied by similar repertoires of morphogenetic tissue movement. We also discovered that cells on contralateral sides of the anterior endoderm are distributed asymmetrically to the dorsal and ventral sides of the anterior intestinal portal, heralding the acquisition of laterality by the embryonic foregut.

Dkk1 and Wnt3 interact to control head morphogenesis in the mouse.

Loss of Dkk1 results in ectopic WNT/beta-catenin signalling activity in the anterior germ layer tissues and impairs cell movement in the endoderm of the mouse gastrula. The juxtaposition of the expression domains of Dkk1 and Wnt3 is suggestive of an antagonist-agonist interaction. The downregulation of Dkk1 when Wnt3 activity is reduced reveals a feedback mechanism for regulating WNT signalling. Compound Dkk1;Wnt3 heterozygous mutant embryos display head truncation and trunk malformation, which are not found in either Dkk1(+/-) or Wnt3(+/-) embryos. Reducing the dose of Wnt3 gene in Dkk1(-/-) embryos partially rescues the truncated head phenotype. These findings highlight that head development is sensitive to the level of WNT3 signalling and that DKK1 is the key antagonist that modulates WNT3 activity during anterior morphogenesis.

Sequential allocation and global pattern of movement of the definitive endoderm in the mouse embryo during gastrulation.

During mouse gastrulation, endoderm cells of the dorsal foregut are recruited ahead of the ventral foregut and move to the anterior region of the embryo via different routes. Precursors of the anterior-most part of the foregut and those of the mid- and hind-gut are allocated to the endoderm of the mid-streak-stage embryo, whereas the precursors of the rest of the foregut are recruited at later stages of gastrulation. Loss of Mixl1 function results in reduced recruitment of the definitive endoderm, and causes cells in the endoderm to remain stationary during gastrulation. The observation that the endoderm cells are inherently unable to move despite the expansion of the mesoderm in the Mixl1-null mutant suggests that the movement of the endoderm and the mesoderm is driven independently of one another.

Genetic interaction of Gsc and Dkk1 in head morphogenesis of the mouse.

Mouse embryos lacking Gsc and Dkk1 function display severe deficiencies in craniofacial structures which are not found in either Dkk1 homozygous null or Gsc homozygous null mutant embryos. Loss of Gsc has a dosage-related effect on the severity of head truncation phenotype in Dkk1 heterozygous embryos. The synergistic effect of these mutations in enhancing head truncation provides direct evidence of a genetic interaction between Gsc and Dkk1, which display overlapping expression in the prechordal mesoderm. In the absence of Gsc activity, the expression of Dkk1, WNT genes and a transgenic reporter for WNT signalling are altered. Our results show that Gsc and Dkk1 functions are non-redundant in the anterior mesendoderm for normal anterior development and Gsc may influence Wnt signalling as a negative regulator.

Definitive endoderm of the mouse embryo: formation, cell fates, and morphogenetic function.

The endoderm is one of the primary germ layers but, in comparison to ectoderm and mesoderm, has received less attention. The definitive endoderm forms during gastrulation and replaces the extraembryonic visceral endoderm. It participates in the complex morphogenesis of the gut tube and contributes to the associated visceral organs. This review highlights the role of the definitive endoderm as a source of patterning cues for the morphogenesis of other germ-layer tissues, such as the anterior neurectoderm and the pharyngeal region, and also emphasizes the intricate patterning that the endoderm itself undergoes enabling the acquisition of regionalized cell fates.