Development of the amniote ventrolateral body wall.

In vertebrates, the trunk consists of the musculoskeletal structures of the back and the ventrolateral body wall, which together enclose the internal organs of the circulatory, digestive, respiratory and urogenital systems. This review gives an overview on the development of the thoracic and abdominal wall during amniote embryogenesis. Specifically, I briefly summarize relevant historical concepts and the present knowledge on the early embryonic development of ribs, sternum, intercostal muscles and abdominal muscles with respect to anatomical bauplan, origin and specification of precursor cells, initial steps of pattern formation, and cellular and molecular regulation of morphogenesis.

Honeycomb sterna: an unusual case of a developmental abnormality in the sternum.

This report details an unusual case of a human sternal developmental abnormality of an anatomical specimen part of the skeletal collection curated by University College London, Anthropology Department skeletal collection. This rarely reported developmental abnormality is caused by the non-fusion of lateral ossification centres in the sternebrae, resulting in the mesosternum having a honeycomb-like appearance. Sternal defects are typically underreported in the clinical literature as many cases being asymptomatic that they are typically diagnosed incidentally, as such there is a dearth in our current understanding of the development and anatomical variants of the sternum. Although in recent years, large-scale CT studies have investigated the prevalence of sternal developmental abnormalities, these studies have not reported sternal defects similar to the individual presented in this report. While most sternal defects are clinically uneventful, the lack of awareness of these variants can result in misinterpretation of radiological and pathological findings as such an understanding of anatomical variants even when asymptomatic is vital.

Dchs1-Fat4 regulation of polarized cell behaviours during skeletal morphogenesis.

Skeletal shape varies widely across species as adaptation to specialized modes of feeding and locomotion, but how skeletal shape is established is unknown. An example of extreme diversity in the shape of a skeletal structure can be seen in the sternum, which varies considerably across species. Here we show that the Dchs1-Fat4 planar cell polarity pathway controls cell orientation in the early skeletal condensation to define the shape and relative dimensions of the mouse sternum. These changes fit a model of cell intercalation along differential Dchs1-Fat4 activity that drives a simultaneous narrowing, thickening and elongation of the sternum. Our results identify the regulation of cellular polarity within the early pre-chondrogenic mesenchyme, when skeletal shape is established, and provide the first demonstration that Fat4 and Dchs1 establish polarized cell behaviour intrinsically within the mesenchyme. Our data also reveal the first indication that cell intercalation processes occur during ventral body wall elongation and closure.

Development of the ventral body wall in the human embryo.

Migratory failure of somitic cells is the commonest explanation for ventral body wall defects. However, the embryo increases ~ 25-fold in volume in the period that the ventral body wall forms, so that differential growth may, instead, account for the observed changes in topography. Human embryos between 4 and 10 weeks of development were studied, using amira reconstruction and cinema 4D remodeling software for visualization. Initially, vertebrae and ribs had formed medially, and primordia of sternum and hypaxial flank muscle primordium laterally in the body wall at Carnegie Stage (CS)15 (5.5 weeks). The next week, ribs and muscle primordium expanded in ventrolateral direction only. At CS18 (6.5 weeks), separate intercostal and abdominal wall muscles differentiated, and ribs, sterna, and muscles began to expand ventromedially and caudally, with the bilateral sternal bars fusing in the midline after CS20 (7 weeks) and the rectus muscles reaching the umbilicus at CS23 (8 weeks). The near-constant absolute distance between both rectus muscles and approximately fivefold decline of this distance relative to body circumference between 6 and 10 weeks identified dorsoventral growth in the dorsal body wall as determinant of the 'closure' of the ventral body wall. Concomitant with the straightening of the embryonic body axis after the 6th week, the abdominal muscles expanded ventrally and caudally to form the infraumbilical body wall. Our data, therefore, show that the ventral body wall is formed by differential dorsoventral growth in the dorsal part of the body.

5, 4, 3, 2, 1: embryologic variants of pentalogy of Cantrell.

BACKGROUND: The purpose of this study was to evaluate our experience with pentalogy of Cantrell and the various embryologic variants. MATERIALS AND METHODS: Patient charts and diagnostic imaging studies of all fetuses evaluated at Texas Children's Fetal Center for pentalogy of Cantrell between April 2004 and June 2014 were reviewed retrospectively. Data collected from patient charts included demographic information, clinical presentation, fetal and postnatal imaging findings, operative treatment, pathologic evaluation, and outcomes. RESULTS: There were 10 patients who presented with embryologic variants of pentalogy of Cantrell over a 6-y period. Two cases displayed the full range of embryologic defects observed, and eight cases exhibited variants of the classic pentalogy. Sternal and pericardial defects were each present in 40% of patients. Additional anomalies present included pulmonary hypoplasia, pulmonary artery stenosis, and chromosomal abnormalities. Four patients presented with diaphragmatic defects but no defect in the pericardium, and one patient presented with a defective pericardium but no associated diaphragmatic defect, suggesting highly specific losses of somatic mesoderm during embryologic development. One patient was lost to follow-up, and a second patient underwent termination of pregnancy. Five of the remaining eight patients survived, one of which had the full range of embryologic defects and now attends preschool but requires speech and occupational therapy. The remaining surviving patients have developed without serious sequelae. CONCLUSIONS: This report highlights the spectrum of anomalies observed in the pentalogy of Cantrell and demonstrates that these fetuses can survive but with substantial morbidity.

Mesenchymal Wnt signaling promotes formation of sternum and thoracic body wall.

Midline defects account for approximately 5% of congenital abnormalities observed at birth. However, the molecular mechanisms underlying the formation of the ventral body wall are not well understood. Recent studies linked mutations in Porcupine-an O-acetyl transferase mediating Wnt ligand acylation-with defects in the thoracic body wall. We hypothesized that anomalous Wnt signaling is involved in the pathogenesis of defective closure of the thoracic body wall. We generated a mouse model wherein Wntless (Wls), which encodes a cargo receptor mediating secretion of Wnt ligands, was conditionally deleted from the developing mesenchyme using Dermo1Cre mice. Wls(f/f);Dermo1(Cre/+) embryos died during mid-gestation. At E13.5, skeletal defects were observed in the forelimbs, jaw, and rib cage. At E14.5, midline defects in the thoracic body wall began to emerge: the sternum failed to fuse and the heart protruded through the body wall at the midline (ectopia cordis). To determine the molecular mechanism underlying the phenotype observed in Wls(f/f);Dermo1(Cre/+) embryos, we tested whether Wnt/ß-catenin signaling was operative in developing the embryonic ventral body wall using Axin2(LacZ) and BatGal reporter mice. While Wnt/ß-catenin signaling activity was observed at the midline of the ventral body wall before sternal fusion, this pattern of activity was altered and scattered throughout the body wall after mesenchymal deletion of Wls. Mesenchymal cell migration was disrupted in Wls(f/f);Dermo1(Cre/+) thoracic body wall partially due to anomalous ß-catenin independent Wnt signaling as determined by in vitro assays. Deletion of Lrp5 and Lrp6 receptors, which mediate Wnt/ß-catenin signaling in the mesenchyme, partially recapitulated the phenotype observed in the chest midline of Wls(f/f);Dermo1(Cre/+) embryos supporting a role for Wnt/ß-catenin signaling activity in the normal formation of the ventral body wall mesenchyme. We conclude that Wls-mediated secretion of Wnt ligands from the developing ventral body wall mesenchyme plays a critical role in fusion of the sternum and closure of the secondary body wall. Thus, impaired Wls activity in the ventral body wall mesenchyme is a mechanism underlying ectopia cordis and unfused sternum.

Regulatory modulation of the T-box gene Tbx5 links development, evolution, and adaptation of the sternum.

The sternum bone lies at the ventral midline of the thorax where it provides a critical attachment for the pectoral muscles that allow the forelimbs to raise the body from the ground. Among tetrapods, sternum morphology is correlated with the mode of locomotion: Avians that fly have a ventral extension, or keel, on their sterna, which provides an increased area for flight muscle attachment. The sternum is fused with the ribs attaching on either side; however, unlike the ribs, the sternal precursors do not originate from the somites. Despite the crucial role of the sternum in tetrapod locomotion, little attention has been given to its acquisition, evolution, and embryological development. We demonstrate an essential role for the T-box transcription factor gene Tbx5 in sternum and forelimb formation and show that both structures share an embryological origin within the lateral plate mesoderm. Consistent with this shared origin and role of Tbx5, sternum defects are a characteristic feature of Holt-Oram Syndrome (OMIM 142900) caused by mutations in TBX5. We demonstrate a link between sternum size and forelimb use across avians and provide evidence that modulation of Tbx5 expression underlies the reduction in sternum and wing size in a flightless bird, the emu. We demonstrate that Tbx5 is a common node in the genetic pathways regulating forelimb and sternum development, enabling specific adaptations of these features without affecting other skeletal elements and can also explain the linked adaptation of sternum and forelimb morphology correlated with mode of locomotion.

A review of the embryological development and associated developmental abnormalities of the sternum in the light of a rare palaeopathological case of sternal clefting.

A sternal cleft or bifid sternum is a rare anterior chest wall abnormality. Although several cases have been reported in clinical literature, very little reference has been made to this anomaly in palaeopathological texts. This paper presents a case of superior sternal clefting observed in a middle-aged female with concurrent Paget's disease and congenital hyperkyphosis excavated from a 19th century Dutch psychiatric asylum cemetery in Bloemendaal, The Netherlands. The embryological development of the sternum and associated developmental abnormalities are reviewed and a differential diagnosis is performed on the suite of observed skeletal anomalies. Goltz syndrome, congenital hypothyroidism, disruption of the Hoxb-4 gene, acute excessive maternal alcohol consumption during pregnancy, Coffin-Lowry syndrome and PHACES syndrome were considered as possible causative agents, with the latter two conditions determined to be the most likely. The psychiatric asylum context, from which the individual came, supports the differential diagnosis as neurological abnormalities are common in these two syndromes. This article demonstrates that the integration of embryology, modern clinical literature and palaeopathological principles is vital in the interpretation of developmental anomalies from an archaeological context.

Development of the rectus abdominis and its sheath in the human fetus.

PURPOSE: Although the rectus abdominis and its sheath are well known structures, their development in the human fetus is poorly understood. MATERIALS AND METHODS: We examined rectus abdominis and sheath development in semiserial horizontal sections of 18 fetuses at 5-9 weeks of gestation. RESULTS: Rectus muscle differentiation was found to commence above the umbilicus at 6 weeks and extend inferiorly. Until closure of the anterior chest wall via fusion of the bilateral sternal anlagen (at 7 weeks), the anterior rectal sheath originated from the external oblique and developed towards the medial margin of the rectus abdominis at all levels, including the supracostal part. After formation of the anterior sheath, fascial laminae from the internal oblique and transversus abdominis contributed to formation of the posterior rectus sheath. However, the posterior sheath was absent along the supracostal part of the rectus abdominis, as the transversus muscle fibers reached the sternum or the midline area. Therefore, it appeared that resolution of the physiological umbilical hernia (8-9 weeks) as well as chest wall closure was not required for development of the rectus abdominis and its sheath. Conversely, in the inferior part of the two largest fetal specimens, after resolution of the hernia, the posterior sheath underwent secondary disappearance, possibly due to changes in mechanical stress. CONCLUSION: Upward extension of the rectus abdominis suddenly stopped at the margin of the inferiorly developing pectoralis major without facing the external intercostalis. The rectus thoracis, if present, might correspond to the pectoralis.

[Development of the skeletal system in utero].

The skeletal system develops from mesenchyme originated from the mesodermal germ layer and neural crest. In view of developmental bone biology, the skeletal system can be divided into four parts : skull, limbs, vertebrae/the ventral column, and ribs/sternum. Bone formation takes place in two ways. In most bones including axial (vertebral column and ribs) and appendicular (limbs) skeletons, a cartilage model first forms and is finally replaced with bone, which is called endochondral ossification. In contrast, most flat bones, such as the majority of bones of the skull, form directly from mesenchymal cells without the prior formation of cartilage ; this type of osteogenesis is called intramembranous ossification. I here discuss development of the skeletal system focusing on its time line in utero.

Chest wall repair with engineered fetal bone grafts: an efficacy analysis in an autologous leporine model.

PURPOSE: We sought to compare the efficacy of engineered fetal bone grafts with acellular constructs in an autologous model of chest wall repair. METHODS: Rabbits (n = 10) with a full-thickness sternal defect were equally divided in 2 groups based on how the defect was repaired, namely, either with an autologous bone construct engineered with amniotic mesenchymal stem cells on a nanofibrous scaffold or a size-matched identical scaffold with no cells. Animals were killed at comparable time-points 18 to 20 weeks postimplantation for multiple analyses. RESULTS: Gross evidence of nonunion confirmed by micro-computed tomography scanning was present in 3 (60%) of 5 of the acellular implants but in no engineered grafts. Histology confirmed the presence of bone in both types of repair, albeit seemingly less robust in the acellular grafts. Mineral density in vivo was significantly higher in engineered grafts than in acellular ones, with more variability among the latter. There was no difference in alkaline phosphatase activity between the groups. CONCLUSIONS: Chest wall repair with an autologous osseous graft engineered with amniotic mesenchymal stem cells leads to improved and more consistent outcomes in the midterm when compared with an equivalent acellular prosthetic repair in a leporine model. Amniotic fluid-derived engineered bone may become a practical alternative for perinatal chest wall reconstruction.

Runx1 and Runx2 cooperate during sternal morphogenesis.

Chondrocyte differentiation is strictly regulated by various transcription factors, including Runx2 and Runx3; however, the physiological role of Runx1 in chondrocyte differentiation remains unknown. To examine the role of Runx1, we generated mesenchymal-cell-specific and chondrocyte-specific Runx1-deficient mice [Prx1 Runx1(f/f) mice and alpha1(II) Runx1(f/f) mice, respectively] to circumvent the embryonic lethality of Runx1-deficient mice. We then mated these mice with Runx2 mutant mice to obtain mesenchymal-cell-specific or chondrocyte-specific Runx1; Runx2 double-mutant mice [Prx1 DKO mice and alpha1(II) DKO mice, respectively]. Prx1 Runx1(f/f) mice displayed a delay in sternal development and Prx1 DKO mice completely lacked a sternum. By contrast, alpha1(II) Runx1(f/f) mice and alpha1(II) DKO mice did not show any abnormal sternal morphogenesis or chondrocyte differentiation. Notably, Runx1, Runx2 and the Prx1-Cre transgene were co-expressed specifically in the sternum, which explains the observation that the abnormalities were limited to the sternum. Histologically, mesenchymal cells condensed normally in the prospective sternum of Prx1 DKO mice; however, commitment to the chondrocyte lineage, which follows mesenchymal condensation, was significantly impaired. In situ hybridization analyses demonstrated that the expression of alpha1(II) collagen (Col2a1 - Mouse Genome Informatics), Sox5 and Sox6 in the prospective sternum of Prx1 DKO mice was severely attenuated, whereas Sox9 expression was unchanged. Molecular analyses revealed that Runx1 and Runx2 induce the expression of Sox5 and Sox6, which leads to the induction of alpha1(II) collagen expression via the direct regulation of promoter activity. Collectively, these results show that Runx1 and Runx2 cooperatively regulate sternal morphogenesis and the commitment of mesenchymal cells to become chondrocytes through the induction of Sox5 and Sox6.

The essential requirement for Runx1 in the development of the sternum.

Runx1 is highly expressed in chondroprogenitor and osteoprogenitor cells and in vitro experiments suggest that Runx1 is important in the early stages of osteoblast and chondrocyte differentiation. However, because Runx1 knockout mice are early embryonic lethal due to failure of hematopoiesis, the role of Runx1 in skeletogenesis remains unclear. We studied the role of Runx1 in skeletal development using a Runx1 reversible knockout mouse model. By crossing with Tie2-Cre deletor mice, Runx1 expression was selectively rescued in the endothelial and hematopoietic systems but not in the skeleton. Although Runx1(Re/Re) embryos survived until birth and had a generally normal skeleton, the development of mineralization in the sternum and some skull elements was significantly disrupted. In contrast to wild-type embryos, the sternum of E17.5 Runx1(Re/Re) embryos showed high levels of Sox-9 and collagen type II expression and lack of development of hypertrophic chondrocytes. In situ hybridization analysis demonstrated that, in contrast to the vertebrae and long bones, the sternum of wild-type embryos expresses high levels of Runx1, but not Runx2, the master regulator of skeletogenesis. Thus, although Runx1 is not essential for major skeletal development, it does play an essential role in the development of the sternum and some skull elements.

PTH stimulated growth and decreased Col-X deposition are phosphotidylinositol-3,4,5 triphosphate kinase and mitogen activating protein kinase dependent in avian sterna.

Type X collagen (Col-X) deposition is a marker of terminal differentiation during chondrogenesis, in addition to appositional growth and apoptosis. The parathyroid hormone/parathyroid hormone related peptide (PTH/PTHrP) receptor, or PPR, is a G-Protein coupled receptor (GPCR), which activates several downstream pathways, moderating chondrocyte differentiation, including suppression of Col-X deposition. An Avian sterna model was used to analyze the PPR GPCR downstream kinase role in growth rate and extracellular matrix (ECM) including Col-II, IX, and X. Phosphatidylinositol kinase (PI3K), mitogen activating protein kinase (MAPK) and protein kinase A (PKA) were inhibited with specific established inhibitors LY294002, PD98059, and H89, respectively to test the hypothesis that they could reverse/inhibit the PTH/PTHrP pathway. Excised E14 chick sterna were PTH treated with or without an inhibitor and compared to controls. Sternal length was measured every 24 hr. Cultured sterna were immuno-stained using specific antibodies for Col-II, IX, or X and examined via confocal microscopy. Increased growth in PTH-treated sterna was MAPK, PI3K, and PKA dose dependent, suggesting growth was regulated through multiple pathways. Col-X deposition was rescued in PTH-treated sterna in the presence of PI3K or MAPK inhibitors, but not with the PKA inhibitor. All three inhibitors moderately disrupted Col-II and Col-IX deposition. These results suggest that PTH can activate multiple pathways during chondrocyte differentiation.

Hernia diafragmática paraesternal de Morgagni-Larrey en adulto / Morgagni-Larrey parasternal diaphragmatic hernia in the adult

Con una prevalencia de 0,3-0,5/1.000 nacimientos, la hernia diafragmática congénita (HDC) sigue siendo una anomalía grave, no bien entendida, alta mortalidad y tratamiento no siempre efectivo. En España se ha informado de una frecuencia del 0,69%oo con una tendencia decreciente en el periodo 1980-2006 del 0,10%oo por año. No obstante, hasta un 5% se diagnostican en adultos durante la realización de un reconocimiento por otra causa. Presentamos un cuadro de vómitos de tres meses de evolución en una mujer de 74 años por hernia diafragmática paraesternal de Morgagni-Larrey (retrocondroesternal, retrocostoxifoidea, retroesternal, subcostal, subesternal o subcostoesternal), que nos ha permitido realizar una actualización de esta patología en adultos y de la morfogénesis del diafragma toracoabdominal. Es en la embriología del diafragma donde encontramos explicación de algunas de sus alteraciones morfológicas y características clínicas, si bien persisten aspectos confusos de la misma. También analizamos el grado de controversia que persiste en algunos aspectos de su tratamiento quirúrgico (vías de acceso, uso o no de mallas y reducción o no del saco herniario). Por lo general priman las técnicas mínimamente invasivas. Consideramos el abordaje laparoscópico como de elección en pacientes adultos con hernia paraesternal candidatos a la cirugía(AU)

With a prevalence of 0.3-0.5/1000 births, congenital diaphragmatic hernia (CDH) remains a serious, poorly understood abnormality with a high mortality rate that cannot always be effectively managed. Its reported frequency in Spain is 0.69%oo with a yearly decreasing trend of 0.10%oo during the period 1980-2006. Up to 5% of cases are incidentally identified in adults undergoing studies for other reasons. We report the case of a 74-year-old woman with vomiting for three months due to parasternal diaphragmatic hernia of Morgagni-Larrey (retrochondrosternal, retrocostoxyphoid, retrosternal, subcostal, substernal or subcostosternal hernia), which allowed us to report an update on this condition in the adult, and on thoracoabdominal diaphragm morphogenesis. It is in the embryology of the diaphragm where an explanation may be found for some morphological changes and clinical manifestations, even though a number of uncertainties remain. We also analyze the extent of controversy persisting on some aspects of surgical treatment (access routes, mesh use, hernial sac reduction). Overall, minimally invasive techniques predominate. We consider laparoscopy the approach of choice for adult patients with parasternal hernia eligible for surgery(AU)

Parathyroid hormone/parathyroid hormone-related peptide modulates growth of avian sternal cartilage via chondrocytic proliferation.

Parathyroid hormone (PTH; 10(-7) to 10(-15) M) decreased terminal chondrogenesis in the avian sterna. During the first half of an 8-day culture, 100 nM PTH (1-34) significantly increased sternal length and downregulated the deposition of type X collagen and its mRNA expression. However, it remains unclear how PTH increased cartilaginous growth. In this study, we examined growth by both cell proliferation and analysis of cyclin d1 and collagen mRNA. Types II, IX, and X collagens and cyclin d1 mRNA were quantified through real-time RT-PCR, while Ki-67 was used as an immunohistochemical proliferation marker. Extracellular matrix content was measured through mRNA quantification of types II, IX, and X collagen and observing deposition of the same collagens. PTH significantly increased the proliferation marker Ki-67 in the sternal cephalic region. There was less type II and X collagen in PTH-treated sterna with concomitant decreases in mRNA production, suggesting that proliferation was the major contributor to cartilage growth in the presence of PTH/PTH-related peptide receptor activation. In conclusion, these experiments demonstrated that PTH increased cartilage growth by upregulating cell proliferation or other extracellular matrix components.

Transient fetal sternal dermal cyst: report of 2 cases and literature review.

OBJECTIVE: The purpose of this series was to describe the prenatal diagnosis and pregnancy outcome of fetuses affected by a transient idiopathic fetal sternal cyst. METHODS: Two fetuses had the diagnosis of an isolated presternal cyst at routine sonography at 15 weeks. A follow-up sonographic examination was done, and the neonates were examined after birth. RESULTS: In both cases, the cyst disappeared at 20 weeks' gestation, and both fetuses had only a small dimple at the location of the cyst. CONCLUSIONS: An isolated presternal cyst is an extremely rare finding. It should be followed sonographically, and if it disappears within a few weeks, the diagnosis of a dermal inclusion cyst should be suspected. Parents can be informed to anticipate a small depression on the neonate's chest.

Hendidura esternal total en un recién nacido y parcial en una niña de 4 años / Cleft sternum: 2 clinical cases

La hendidura esternal es una malformación congénita de la pared torácica que se origina en una falla embrionaria de la fusión de las valvas esternales en la línea media. El defecto debe ser reparado precozmente al nacer, para reestablecer la protección ósea de las estructuras del mediastino, prevenir el movimiento paradojal de las vísceras en la respiración, eliminar la deformidad visible y permitir un desarrollo normal de la caja torácica. Objetivo: Notificar 2 pacientes portadores de esta infrecuente malformación y revisar sus características clínicas, permitiendo realizar un diagnostico preciso, orientar el estudio y definir un adecuado tratamiento. Casos clínicos: Recién nacido masculino con una hendidura esternal completa que provoca un "distress" respiratorio y una preescolar de 4 años, con una hendidura parcial del tercio superior esternal, asociada a una cardiopatía congénita operada. Los pacientes son sometidos a una reparación quirúrgica que permitió un alta precoz y una evolución clínica favorable. Conclusión: La Hendidura Esternal es una malformación de baja frecuencia que debe ser corregida precozmente para evitar el uso de técnicas de mayor complejidad con resultados variables.

Sternal cleft: a surgical opportunity.

PURPOSE: The aim of this study was to evaluate the results from the surgical techniques utilized to repair congenital sternal cleft. METHODS: From January, 1987 to January, 2001, 5,182 patients were seen for chest wall malformations. Eight (0.15%) had sternal cleft. The age at presentation ranged from 15 days to 5 years. Six were girls (75%). The associated malformations were congenital cardiac malformations (2 patients), maxillofacial hemangioma (1 patient). All of them underwent a surgical repair, which could be classified into 3 methods: group 1 had primary closure of the defect (3 patients); group 2 underwent partial resection of the first, second, and third costal cartilages, disruption of the sternoclavicular junction, and closure of the sternal bars with stainless steel wire (3 patients); and group 3 had mobilization and approximation of the sternocleidomastoid muscles with closure achieved with costal homograft and prosthetic mesh (2 patients). The interval for postoperative follow-up was 1 to 8 years. RESULTS: Group 1 patients developed well, although 2 of them had a slight degree of pectus excavatum in the long term not requiring surgical correction. Group 2 Patients developed without problems in all cases. One of the patients from group 3 had unsatisfactory aesthetic and functional results. He underwent reoperation with the second technique, achieving an improved result. CONCLUSIONS: Primary closure of the sternal cleft is the easiest technique. It should be performed in young infants. In the long term it can lead to a mild degree of pectus excavatum. The costal cartilage resection with mobilization of the clavicle achieved excellent results and allowed ready approximation of both sternal halves avoiding the use of costal grafts and prosthetic material.

Inductive signals from the somatopleure mediated by bone morphogenetic proteins are essential for the formation of the sternal component of avian ribs.

The posterior five pairs of avian ribs are composed of vertebral and sternal components, both derived from the somitic mesoderm. For the patterning of the rib cartilage, inductive signals from neighboring tissues on the somitic mesoderm have been suggested to play critical roles. The notochord and surface ectoderm overlying the somitic mesoderm are essentially required for the development of proximal and distal regions of the ribs, respectively. Involvement of the somatopleure in rib development has already been suggested but is less understood than those of the notochord and surface ectoderm. In this study, we reinvestigated the role of the somatopleure during rib development. We first identified the chicken homologue of the mouse Mesenchymal forkhead-1 (cMfh-1) gene based on sequence similarities. cMfh-1 was observed to be expressed in the nonaxial mesoderm, including the somitic mesoderm, and, subsequently, in cartilage forming the ribs, vertebrae, and appendicular skeletal system. In the interlimb region, corresponding to somites 21-25 (or 26), cMfh-1-positive somitic mesoderm was seen penetrating the somatopleure of E4 embryos, and cMfh-1 was used as a molecular marker demarcating prospective rib cartilage. A series of experiments affecting the penetration of the somitic mesoderm into the somatopleure was performed in the present study, resulting in defects in sternal rib formation. The inductive signals emanating from the somatopleure mediated by BMP family proteins were observed to be essentially involved in the ingrowth of the somitic mesoderm. BMP4 alone, however, could not completely replace inductive signals from the somatopleure, suggesting the involvement of additional signals for rib formation.