[Diagnosis of prostate capsular invasion by pelvic magnetic resonance imaging and serum level of prostate specific antigen]

Transrectal ultrasonography (TRUS), computed tomography (CT), and magnetic resonance imaging (MRI) are employed to diagnose the clinical stage of prostate cancer. However, several cases are diagnosed as pathological stage pT3 after total prostatectomy. We investigated the accuracy of the evaluation of pathologic capsular penetration by preoperative pelvic MRI and preoperative serum PSA level and capsular penetration. The diagnostic accuracy of capsular penetration by MRI was 63.3%. On the other hand, the diagnostic accuracy of capsular penetration by preoperative PSA was 89.7% when its cut off value was 17 ng/ml. We conclude that preoperative serum PSA level could be more useful to diagnose accurately stage of prostate cancer than pelvic MRI.

[Study of neoadjuvant chemotherapy for invasive bladder cancer with MEC (methotrexate, epirubicin, cisplatin) therapy]

Eighteen patients with locally invasive bladder cancer were treated with 1 or 2 cycles of neoadjuvant chemotherapy consisting of methotrexate, epirubicin and cisplatin (MEC). All patients underwent radical cystectomy and pelvic lymph node dissection. Down-staging was observed in twelve (complete pathological response in 3 and partial pathological response in 9) patients (response rate were 67%). Four of the 18 patients died of disease and all of them had not achieved down-staging. Multivariate analysis revealed nodal status to be the only independent predictor. With regard to side effects, gastrointestinal symptoms and myelo-suppression were observed in almost all patients. Thrombocytopenia was observed in 13 patients (72%) including 7 patients who showed symptoms over grade 3. Gastro-intestinal symptoms and leukocytopenia disappeared with granisetron and granulocyte colony stimulating factor. There were no treatment-related deaths in this study. These results indicate that MEC therapy was safely performed and showed a high response rate in patients with locally invasive bladder cancer.

[Clinical outcome and analysis of radical prostatectomy in clinical stage B and C prostate cancer]

Between 1989 and 1999, 40 patients treated with radical prostatectomy for clinical stage B and C prostate cancer were analyzed. Prostate-specific antigen (PSA) failure after radical prostatectomy occurred in four patients, and one of them died of clinical recurrence of prostate cancer. Cause-specific survival at 5 years was 91.7% and PSA failure-free rate at 5 years was 76.8%. Staging accuracy of CT and MRI image was not satisfactory. In 41.7% patients, extracapsular extension can not be determined. Preoperative serum PSA levels of pathologically organ-confined disease (OCD) patients were significantly lower than those of pathologically non-OCD patients. Further analysis indicated that preoperative serum PSA levels of greater than 20.1 ng/ml are useful predictors for pathologically non-OCD.

Differential expression of two BMP antagonists, gremlin and Follistatin, during development of the chick feather bud

Expression of four BMP antagonist genes, noggin, chordin, gremlin and Follistatin, was examined during chick feather development. Although expression of noggin and chordin was not detected, gremlin and Follistatin were expressed differentially in feather buds. The differential expression patterns of gremlin and Follistatin change dynamically from the nascent inter-feather bud region to the posterior domain of the feather bud.

Cloning and expression of the chick p63 gene

We have isolated a chick cDNA for p63, a member of the p53 transcription factor family. This cDNA encodes a protein of 582 amino acids for an alpha isoform in the C-terminal region, while lacking the N-terminal transactivation domain. The chick p63 gene is first expressed in the prospective cutaneous ectoderm at stage 6 and later in the developing epithelia. The p63 expression is intense in specialized epithelial structures, such as apical ectodermal ridge of the limb bud, epithelia of branchial arches and feather buds. Furthermore, we have found that the transcripts are detected in the interdigital epithelium, intersomite epithelium, and epaxial dermamyotome.

Coagulation profile, hepatic function, and hemodynamics following Fontan-type operations

We analyzed retrospectively the relationship between coagulation profile, and either hepatic function or hemodynamics, in patients who had undergone a Fontan-type procedure, comparing them, first, with a control group of 12 patients without significant hemodynamic abnormality, and, second, with a group of 14 patients who had not undergone a Fontan procedure, but whose mean right atrial pressure exceeded 8 mmHg. Follow-up catheterization had been performed in all 30 patients submitted to the Fontan-type operation. Prothrombin time, and factor XIII, were significantly lower in those who had undergone the Fontan procedure than in the other groups. Those submitted to the Fontan operation also had lower levels of protein C than controls, and their levels of plasminogen were lower than the patients with high right atrial pressure. Both aspartate aminotransferase and alanine aminotransferase were higher in those undergoing the Fontan procedure than in the other groups, while gamma-glutamyltranspeptidase in these patients was higher than in the control group. Mean right atrial pressure was highest in those undergoing the Fontan procedure, while cardiac index was lowest. Prothrombin time was correlated to some extent with aspartate aminotransferase, mean right atrial pressure, and cardiac index. Protein C correlated with both aspartate aminotransferase and mean right atrial pressure, while factor XIII correlated with alanine aminotransferase, mean right atrial pressure, and cardiac index. Aspartate aminotransferase, alanine aminotransferase, and gamma-glutamyltranspeptidase, parameters of hepatic function, correlated significantly with mean right atrial pressure. In those who had undergone the Fontan procedure, decreased synthesis of pro-and anti-coagulant factors is a risk factor for both thrombosis and bleeding. Abnormal hemodynamics, in the absence of a right sided pumping chamber, may predispose to subclinical hepatic dysfunction, leading to selective disturbances of protein synthesis.

[Study of free to total prostate specific antigen ratio in the detection of patients with prostate cancer]

BACKGROUND

We investigated the clinical usefulness of free to total serum prostate specific antigen (PSA) ratio (F/T ratio) in order to improve the specificity of total PSA measurement for detecting prostate cancer.

METHOD

In this study 129 patients with total PSA level 4-20 ng/ml underwent transrectal ultrasound guided sextant biopsy. Serum samples were assessed for total PSA, free PSA and the F/T ratio calculated. All patients were pathologically diagnosed as benign prostatic hyperplasia or prostate cancer.

RESULTS

Of 129 patients 21 had prostate carcinoma (PCa) and 108 had benign prostatic hyperplasia (BPH) from the results of prostate biopsies. The mean of total PSA were not significantly different between men with PCa and with BPH. The mean of free PSA for PCa was significantly lower than that for BPH (p = 0.043). Furthermore, the mean of F/T ratio was significantly different between PCa and BPH group (p = 0.0014). The F/T ratio had a higher specificity than total PSA at all levels of sensitivity in detecting prostate cancers. Sensitivity, specificity and accuracy for cancer detection at a cut off 0.12 was 90.4%, 51.8% and 58.1%, respectively. Also, free PSA was as useful as F/T ratio for cancer detection when analyzed in receiver operating characteristic curves analysis. When determined the cut off number of free PSA at 0.78 ng/ml, the sensitivity, specificity and accuracy for cancer detection were 61.9%, 66.7% and 65.9%, respectively.

CONCLUSION

This study indicated that the F/T ratio and free PSA could improve the specificity without impairing the sensitivity for detecting PCa in patients with 4-20 ng/ml of total PSA.

Abnormal cardiac autonomic nervous activity after right ventricular outflow tract reconstruction

BACKGROUND

There are few studies of cardiac autonomic nervous activity (CANA) in patients with congenital heart disease. Methods and Results-We evaluated CANA in 54 patients after closure of an atrial/ventricular septal defect (group A), 54 patients after successful right ventricular outflow tract reconstruction (RVOTR) (group B1), 35 RVOTR patients with residual stenosis (group B2), and 47 controls. Cardiac parasympathetic nervous activity (PSNA) was estimated by heart rate (HR) change after cholinergic blockade, HR variability, and arterial baroreflex sensitivity (BRS). Cardiac sympathetic nervous activity was estimated by the heart-to-mediastinum (123)I-metaiodobenzylguanidine activity ratio (H/M) and HR increase after isoproterenol infusion (ss). HR response (DeltaHR) and peak oxygen uptake (VO(2)) were measured by exercise test. There was no difference in ss among study groups. Group A exhibited mildly impaired PSNA, which recovered 1 year after surgery, and no change in H/M. Impaired PSNA and low H/M were found in groups B1 and B2 compared with controls (P<0.001), although the PSNA tended to recover 1 year after re-RVOTR. In group B1, PSNA and ss were related to DeltaHR, and BRS correlated inversely with the number of surgical procedures and age at RVOTR and positively correlated with the follow-up period, whereas DeltaHR correlated with peak VO(2) (P<0.01 to 0.001).

CONCLUSIONS

After RVOTR, postsynaptic ss-sensitivity is maintained and is important in DeltaHR during exercise, as is PSNA, although ventricular sympathetic denervation is common. Impaired PSNA immediately after RVOTR improves with improved DeltaHR and results in future amelioration of aerobic capacity, whereas ventricular sympathetic reinnervation is uncertain.

FGF10 acts as a major ligand for FGF receptor 2 IIIb in mouse multi-organ development

FGF receptor 2 isoform IIIb (FGFR2b), originally discovered as a receptor for FGF7, is known to be an important receptor in vertebrate morphogenesis, because FGFR2b null mice exhibit agenesis or dysgenesis of various organs, which undergo budding and branching morphogenesis. Since FGF7 null mice do not exhibit marked defects in organogenesis, it has been considered that other FGF(s) than FGF7 might function as a major ligand for FGFR2b during organogenesis. One of the candidate ligands is FGF10, because FGF10 binds to FGFR2b with high affinity and the formation of the limb and lung is arrested in FGF10 null mice as found in FGFR2b-deficient mice. Previous analyses of FGF10 null mice revealed that FGF10 is required for limb and lung development. To elucidate the role of FGF10 in wide-range organogenesis, we further analyzed the phenotypes of the FGF10 knockout mice. We found diverse phenotypes closely related to those for FGFR2b-deficient mice, which includes the absence of thyroid, pituitary, and salivary glands, while minor defects were observed in the formation of teeth, kidneys, hair follicles, and digestive organs. These results suggest that FGF10 acts as a major ligand for FGFR2b in mouse multi-organ development.

Correlation of diversity of leg morphology in Gryllus bimaculatus (cricket) with divergence in dpp expression pattern during leg development

Insects can be grouped into mainly two categories, holometabolous and hemimetabolous, according to the extent of their morphological change during metamorphosis. The three thoracic legs, for example, are known to develop through two overtly different pathways: holometabolous insects make legs through their imaginal discs, while hemimetabolous legs develop from their leg buds. Thus, how the molecular mechanisms of leg development differ from each other is an intriguing question. In the holometabolous long-germ insect, these mechanisms have been extensively studied using Drosophila melanogaster. However, little is known about the mechanism in the hemimetabolous insect. Thus, we studied leg development of the hemimetabolous short-germ insect, Gryllus bimaculatus (cricket), focusing on expression patterns of the three key signaling molecules, hedgehog (hh), wingless (wg) and decapentaplegic (dpp), which are essential during leg development in Drosophila. In Gryllus embryos, expression of hh is restricted in the posterior half of each leg bud, while dpp and wg are expressed in the dorsal and ventral sides of its anteroposterior (A/P) boundary, respectively. Their expression patterns are essentially comparable with those of the three genes in Drosophila leg imaginal discs, suggesting the existence of the common mechanism for leg pattern formation. However, we found that expression pattern of dpp was significantly divergent among Gryllus, Schistocerca (grasshopper) and Drosophila embryos, while expression patterns of hh and wg are conserved. Furthermore, the divergence was found between the pro/mesothoracic and metathoracic Gryllus leg buds. These observations imply that the divergence in the dpp expression pattern may correlate with diversity of leg morphology.

Development and clinical application of minimally invasive cardiac surgery using percutaneous cardiopulmonary support

OBJECTIVES

Optimal cardiopulmonary support during minimally invasive cardiac surgery remains controversial. We developed cardiopulmonary bypass for minimally invasive cardiac surgery using percutaneous peripheral cannulation.

METHODS

Subjects were 34 patients (age: 58 +/- 13 years; range: 17-73) undergoing minimally invasive cardiac surgery using percutaneous cardiopulmonary support between June 1997 and March 1999. Procedures included atrial septal defect closure (n = 14), partial atrioventricular septal defect closure (n = 1), mitral valve replacement (n = 8), mitral valve repair (n = 3), aortic valve replacement (n = 6), coronary artery bypass grafting (n = 1), and right atrial myxoma extirpation (n = 1). Bicaval venous drainage from the right internal jugular vein and the femoral vein and arterial return to the femoral artery were instituted by percutaneous cannulation. Venous drainage was implemented by negative pressure (-20 to -40 mmHg) and arterial return was by conventional roller pump. All procedures were conducted through a skin incision 8 +/- 1 cm, from 6 to 10 cm and partial sternotomy. Aortic cross clamping and cardioplegic solution were administered in the surgical field.

RESULTS

The operation lasted 224 +/- 45 min., cardiopulmonary bypass 104 +/- 32 min., and aortic clamping 77 +/- 23 min.. No deaths occurred. One patient with residual atrial septal defect required reoperation through the same skin incision. Only 1 patient required homologous blood transfusion. The average postoperative hospital stay was 15 +/- 5 days.

CONCLUSIONS

Minimally invasive cardiac surgery using percutaneous cardiopulmonary support is safe and an excellent option for selected patients affected by single valve lesion, simple cardiac anomalies, and coronary artery bypass grafting.

Inhibition of disease flare with diethylstilbestrol diphosphate and chlormadinone acetate administration for two weeks prior to slow-releasing leuprolide acetate in prostatic cancer patients

To determine whether administration of estrogen or gestagen prior to luteinizing hormone-releasing hormone (LH-RH) agonist prevents disease flare in prostate cancer patients, we pretreated the patients with either diethylstilbestrol diphosphate (DES-P) 300 mg daily (N = 17) or chlormadinone acetate (CMA) 100 mg daily (N = 16) or none (N = 16) for two weeks before the initial injection of leuprolide acetate (L). Blood samples for prostatic specific antigen (PSA), testosterone (T), and luteinizing hormone were collected before CMA and DES-P administration, before and at 2, 7, 14, 28, 56, and 84 days after the first administration of leuprolide. The treatment with DES-P and CMA prior to LH-RH agonist induced an early decline of PSA. The mean PSA level showed no significant secondary rise in those patients with pretreatment after L administration. In the patients pretreated with DES-P or CMA, the mean serum T level never exceeded the pretreatment baseline after L administration. On the other hand, in the patients without DES-P or CMA, both serum T and PSA levels increased after the first administration of L. These results clearly demonstrate that pretreatment with DES-P 300 mg daily or CMA 100 mg daily for 2 weeks is quite effective to prevent disease flare after the first administration of L in patients with prostatic cancer.

Global myocardial ischemia as a complication of an acute type A aortic dissection--rapid diagnosis of a case by transesophageal echocardiography

A 36-year-old female was admitted for severe chest pain followed by profound shock. Electrocardiography showed severe ST segment depression (0.5-0.7 mV) in all leads except aVR and aVL. Echocardiography revealed an intimal flap in the ascending aorta and coexisting grade 3 aortic regurgitation. She was immediately intubated and transferred to the intensive care unit. Transesophageal echocardiography (TEE) demonstrated an intimal tear at 2 cm above the sinotubular junction, and the ostium of the left main trunk was oppressed by the intimal flap during diastole. Emergency graft replacement of the ascending aorta and aortic hemiarch concomitant with aortic valve resuspension was performed successfully. The ECG changes reversed to normal immediately after the operation. The patient was extubated 2 days postoperatively and discharged from the hospital 14 days postoperatively. TEE is useful for the rapid evaluation of coronary malperfusion as a complication of acute aortic dissection, especially in patients with hemodynamic instability.

Involvement of fibroblast growth factor (FGF)18-FGF8 signaling in specification of left-right asymmetry and brain and limb development of the chick embryo

To elucidate roles of fibroblast growth factors (FGF)18 during vertebrate development, we examined expression patterns of Fgf18 in chick embryos and observed effects of FGF18 protein on the Hensen's node, isthmus, and limb buds. Fgf18 is expressed on the right side of the node before the expression of Fgf8 starts. FGF18 protein can induce expression of Fgf8 on the left side of the node, indicating involvement of both FGFs in specification of left-right asymmetry. In the developing brain, Fgf18 is expressed in the isthmus, following the Fgf8 expression. Since Fgf18 is induced ectopically during formation of the second midbrain by FGF8 protein, both FGFs also elaborate midbrain development. In the limb bud, Fgf18 is expressed in the mesenchyme and ectopic application of FGF18 protein inhibits bone growth in the limb. FGF18 is thus likely an endogenous ligand of FGF receptor 3, whose mutation causes bone dysplasia in humans. These results demonstrate that the FGF18-FGF8 signaling is involved in various organizing activities and the signaling hierarchies between FGF18 and FGF8 seem to change during patterning of different structures.

Clinical effects of ventricular assist system in end-stage cardiac failure. Advantages of left ventricular blood drainage for recovery from cardiac dysfunction

OBJECTIVES

Heart transplantation is extremely limited currently in Japan. As a consequence ventricular assist system implantation is employed the patient falls into end-stage cardiogenic shock. This preliminary report describes our initial clinical experience with use of 2 kinds of ventricular assist system for 13 Japanese patients.

METHODS

7 patients were supported by a left ventricular assist system with blood drainage from the left atrium (LA drainage Group) using a Toyobo ventricular assist system, while another 6 patients were supported by a left ventricular assist system with blood drainage from the left ventricle (LV drainage Group) using the Toyobo ventricular assist system (1 patient) or TCI-LVAS (5 patients).

RESULTS

The average duration of ventricular assist system support in the LV drainage Group was 112 days including two on-going patients (now at 39 days and 241 days) and in the LA drainage Group was 49 days. The average left ventricular ejection fraction at 3 weeks after ventricular assist system implantation was improved from 12.3 to 54% using the TCI-LVAS and from 14 to 33% using the Toyobo ventricular assist system with drainage from the left ventricle. However, this was decreased from 20 to 10% using the Toyobo ventricular assist system with drainage from the left atrium. The ventricular assist system was explanted in 4 patients (31%) with recovery of cardiac dysfunction and 3 were long survivors. The 2 on-going patients are awaiting heart transplantation. Thus the current survival rate overall is 38%. The survival rate (67%) is excellent in the LV drainage Group including 2 long survivors after explantation.

CONCLUSION

Ventricular assist system support with drainage from the left ventricle seems to be more advantageous for cardiac functional recovery than from the left atrium for end-stage heart failure.

Ventilatory response to exercise in patients with major aortopulmonary collateral arteries after definitive surgery

Patients with pulmonary atresia and major aortopulmonary collateral arteries (MAPCAs) may be at risk for both ventilatory impairment and abnormal pulmonary circulation after definitive surgery. We measured the ventilatory response to exercise in 16 patients with MAPCAs after definitive surgery (group A) and compared the results with those in 16 patients with tetralogy of Fallot with pulmonary atresia and without MAPCAs after definitive operation (group B), with 24 patients with tetralogy of Fallot after one-stage repair without previous palliation (group C), and with 48 healthy subjects (group D). Pulmonary function and treadmill exercise tests were performed. Arterial blood gases were also analyzed and the dead space to tidal volume ratio calculated. In group A, the vital capacity, diffusion capacity, and peak oxygen uptake were lowest (p <0.001), whereas the ventilatory equivalent for carbon dioxide was highest and its value at peak exercise correlated with age at time of surgery (r = 0.73, p <0.002). The arterial oxygen tension decreased progressively in group A and its value at peak exercise inversely correlated with the mean pulmonary artery pressure in all patients (r = -0.75, p <0.001). The arterial carbon dioxide tension decreased significantly at peak exercise in controls but showed no change in group A. The dead space to tidal volume ratio decreased during exercise in patients without MAPCAs and in controls but increased in group A, and the dead space to tidal volume ratio at peak exercise was inversely correlated with vital capacity in all patients (r = -0.77, p <0.001). Diffusion capacity independently predicted arterial carbon dioxide tension and dead space ventilation during exercise. Marked restrictive ventilatory impairment with low diffusion capacity along with a pulmonary obstructive change contributed to the abnormal pulmonary gas exchange during exercise in group A. Earlier repair of MAPCAs may prevent the progression of the impaired ventilatory response to exercise in these patients.

Heart rate recovery after exercise and cardiac autonomic nervous activity in children

To investigate the difference in heart rate (HR) recovery after exercise between children and young adults, we administered a constant load of light exercise intensity and progressive treadmill exercise tests to nine children (aged 9 to 12 y, group A) and eight young adults (six male and two female, aged 17 to 21 y, group B) who had a history of Kawasaki disease without significant coronary arterial lesions. HR after both exercise protocols was analyzed. The low-frequency (LF) and high-frequency (HF) components of HR variability were measured, and LF/HF was calculated (log LF, log HF, log L/H). Arterial baroreflex sensitivity was assessed by the phenylephrine method. There were no differences between groups A and B in resting HR, peak HR, peak oxygen uptake, and decreases in systolic blood pressure during the recovery period. HR 1 and 2 min after peak exercise and 1 min after constant-load exercise was significantly lower in group A than in group B (p < 0.05), and the changes in HR from peak values after both exercise tests were also greater in group A than in group B (p < 0.05-0.01). Although no difference in arterial baroreflex sensitivity was observed, log HF was significantly higher in group A than in group B (p < 0.01), and log L/H was significantly lower in group A than in group B (p < 0.05). The value of log HF correlated inversely with the decrease in HR immediately after both exercise protocols (p < 0.05-0.01). Although log L/H correlated with the decrease in HR after peak exercise (p < 0.05-0.0005), the early decline in HR after constant-load exercise did not correlate with log L/H. Arterial baroreflex sensitivity did not correlate with the decrease in HR at any recovery time. These data suggest that the early phase of HR recovery after light to severe exercise is influenced by the cardiac parasympathetic nervous activity at rest and that the greater central cholinergic modulation of HR in children than in young adults may be responsible in part for children's faster HR recovery after exercise.

Asymmetric expression of antivin/lefty1 in the early chick embryo

Mammalian lefty and zebrafish antivin, highly related to lefty, are shown to be expressed asymmetrically and involved in the specification of the left body side of early embryos. We isolated a chick homologue of the antivin/lefty1 cDNA and studied its expression pattern during early chick development. We found that antivin/lefty1 is expressed asymmetrically on the left side of the prospective floorplate, notochord and lateral plate mesoderm of the chick embryo.

Mouse Pitx2 deficiency leads to anomalies of the ventral body wall, heart, extra- and periocular mesoderm and right pulmonary isomerism

Pitx2, a bicoid-related homeobox gene, is involved in Rieger's syndrome and the left-right (L-R) asymmetrical pattern formation in body plan. In order to define the genomic structure and roles of Pitx2, we analyzed the genomic structure and generated Pitx2-deficient mice with the lacZ gene in the homeobox-containing exon of Pitx2. We were able to show that among three isoforms of Pitx2, Pitx2c shows asymmetrical expression whereas Pitx2a, Pitx2b and Pitx2c show symmetrical expression. In Pitx2(-)(/)(-) embryos there was an increase in mesodermal cells in the distal end of the left lateral body wall and an amnion continuous with the lateral body wall thickened in its mesodermal layer. These changes resulted in a failure of ventral body wall closure. In lung and heart in which Pitx2 is expressed asymmetrically, right pulmonary isomerism, atrioventricular canals with prominent swelling, and juxtaposition of the atrium were detected. The hearts failed to develop tricuspid and mitral valves and a common atrioventricular valve forms. Further, dysgenesis of the Pitx2(-)(/)(-) extraocular muscle and thickening of the mesothelial layer of cornea were observed in the ocular system where Pitx2 is expressed symmetrically, and these resulted in enophthalmos. The present study shows that Pitx2 expressed in various sites participates in morphogenesis through three types of actions: the involvement of asymmetric Pitx2 expression in the entire morphogenetic process of L-R asymmetric organs; the involvement of asymmetric Pitx2 expression in the regional morphogenesis of asymmetric organs; and finally the involvement of symmetric Pitx2 expression in the regional morphogenesis of symmetric organs.

FGF10 can induce Fgf8 expression concomitantly with En1 and R-fng expression in chick limb ectoderm, independent of its dorsoventral specification

The limb bud has a thickened epithelium at the dorsal-ventral boundary, the apical ectodermal ridge (AER), which sustains limb outgrowth and patterning. A secreted molecule fibroblast growth factor (FGF)10 is involved in inducing Fgf8 expression in the prospective AER and mutual interaction between mesenchymal FGF10 and FGF8 in the AER is essential for limb outgrowth. A secreted factor Wnt7a and a homeobox protein Lmx1 are involved in the dorsal patterning of the limb, whereas a homeobox protein Engrailed 1 (En1) is involved in the dorsal-ventral patterning as well as AER formation. Radical fringe (R-fng), a vertebrate homolog of Drosophila fringe was also found to elaborate AER formation in chicks. However, little is known about the molecular interactions between these factors during AER formation. The present study clarified the relationship between FGF10, Wnt7a, Lmx1, R-fng and En1 during limb development using a foil-barrier insertion experiment. It was found that a foil-barrier inserted into the chick prospective wing mesenchyme lateral to the mesonephric duct blocks AER induction. This experiment was expanded by implanting Fgf10-expressing cells lateral to the barrier and examined whether FGF10 could rescue the expression of the limb-patterning genes reported in AER formation. It was found that FGF10 is sufficient to induce Fgf8 expression in the ectoderm of the foil-inserted limb bud, concomitantly with R-fng and En1 expression. However, FGF10 could not rescue the expression of the dorsal marker genes, Wnt7a or Lmx1. Thus, it is suggested that epithelial factors of En1 and R-fng can induce Fgf8 expression in the limb ectoderm in cooperation with a mesenchymal factor FGF10. Some factor(s) other than FGF10, possibly from the paraxial structures medial to the limb mesoderm, is responsible for the initial dorsal-ventral specification of the limb bud.

FGFR2 signaling in normal and limbless chick limb buds

FGF10 and FGF8, which are reciprocally expressed by the mesoderm and AER of the developing limb bud, have been implicated in limb initiation, outgrowth, and patterning. FGF10 and FGF8 signal through the FGFR2b and FGFR2c alternative splice isoforms, respectively [Ornitz DM, et al. 1996. J Biol Chem 271:15292-15297; Igarashi M, et al. 1998. J Biol Chem 273:13230-13235]. A paracrine signaling loop model has been proposed whereby FGF10 expressed by limb mesoderm signals via ectodermally restricted FGFR2b to regulate FGF8 expression by the apical ectoderm; in turn, FGF8 signals via mesodermally restricted FGFR2c to maintain FGF10 expression [Ohuchi H, et al. 1997. Development 124:2235-2244; Xu X, et al. 1998. Development 125:753-765]. To explore this model, we have examined FGFR2b and FGFR2c mRNA expression, using isoform-specific probes during the early stages of development of the chick limb when limb initiation, AER induction, and outgrowth are occurring. We have found that FGFR2b is expressed by limb ectoderm, including the AER, consistent with paracrine signaling of FGF10. By contrast, FGFR2c is expressed by both mesoderm and ectoderm, indicating that FGF8 has the potential to function in an autocrine as well as paracrine fashion. Indeed, as the limb grows out in response to the AER, FGFR2c expression attenuates in the mesoderm of the progress zone, but is maintained in the AER itself, arguing against exclusive paracrine signaling of FGF8 during limb outgrowth. We also report that transcripts for FGF10, FGFR2b, and FGFR2c are expressed normally in the limb buds of limbless mutant embryos, which fail to form an AER and do not express FGF8. Furthermore, we detect no mutations in exons specific for the FGFR2c or FGFR2b isoforms in limbless embryos. Since gene targeting has shown that expression of FGF8 in limb ectoderm depends on FGF10 [Min H, et al. 1998. Genes Dev 12:3156-3161; Sekine K, et al. 1999. Nature Genet 21:138-141], these results indicate that the product of the limbless gene is required for FGF10 to induce expression of FGF8.