Origin of mesenchymal tissue in the septum primum: A structural and ultrastructural study

Arrechedera, Héctor; Álvarez, Mabel; Strauss, Maurice J.; Ayesta, C.

doi:10.1016/s0022-2828(87)80372-3

Cited by 27 publications

(23 citation statements)

References 19 publications

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“…Thus, the temporal sequence of development suggests that the mesenchyme on the leading edge of the PAS arises in much the same manner as do the atrioventricular endocardial cushions within the atrioventricular canal. This interpretation is supported by the findings of Arrechedera et al, 20 who showed that the endocardial cells covering the PAS in the chick behaved as did those of the endocardial cushions when the latter transformed into mesenchyme, and, more recently, by the study of Gerety and Watanabe. 28 In addition, the homeobox gene Msx-1, which is expressed in atrioventricular endothelium at the time it undergoes an epithelial-mesenchymal transformation, is also expressed in the developing PAS.…”

Section: What Then Is the Spina Vestibuli?supporting

confidence: 55%

Formation of the Atrioventricular Septal Structures in the Normal Mouse

Webb

Brown

Anderson

1998

Circulation Research

141

126

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—It is sometimes thought that formation of the atrioventricular septum is equated with fusion of the endocardial cushions and that failure of fusion can explain all deficiencies of atrioventricular septation. Clearly, this is simplistic, but the exact contribution of different primordia to atrioventricular septation is not well understood. To clarify this, we studied normal mouse embryos (days 10 to 15 of gestation), which were serially sectioned and examined by light microscopy. Another group of embryos was examined by scanning electron microscopy after microdissection. Our results show that development of the atrioventricular septal area is highly complex. Proper formation requires the following: remodeling of the inner heart curvature, rotation of the horns of the systemic venous sinus around the pulmonary portal, expansion of the right atrioventricular junction, formation of the muscular atrial and ventricular septa, bridging by the dextrodorsal outflow ridge and the superior endocardial cushion, fusion with the inferior margins of the venous valves, and formation of the mouth of the coronary sinus from the cranial muscular wall of the left sinus horn. Multiple primordia contribute to a central mesenchymal mass (the “septum intermedium”), including the mesenchyme on the leading edge of the primary atrial septum, the atrioventricular endocardial cushions, and the cap of mesenchyme on the spina vestibuli. Fusion of these components closes the ostium primum, completing atrial and atrioventricular septation. Additionally, the spina vestibuli has a mesodermal core, which contributes to the muscularization of the lower margin of the oval fossa. This contrasts with the formation of the upper rim, which occurs as a result of an infolding of the atrial wall itself.

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Section: What Then Is the Spina Vestibuli?supporting

confidence: 55%

Formation of the Atrioventricular Septal Structures in the Normal Mouse

Webb

Brown

Anderson

1998

Circulation Research

141

126

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“…In Tie2-Cre/R26R double transgenic embryos, which show the lineage of tissues derived from the endocardium, the AV cushions and the cap on the leading edge of the primary muscular atrial septum are marked, as previously suggested. 19,20 Sections from these embryos also show that the mesenchymal cells in the dorsal part of the heart, contiguous with the dorsal mesocardium, are not derived from the endocardium. Because the only known source of cardiac mesenchyme at the venous pole of the heart is that derived by transformation from endocardium, we presume that these additional mesenchymal cells take their origin from outside the heart.…”

Section: Discussionmentioning

confidence: 91%

“…19,21 Given these ambiguities in the description of the spine by the different authors it is difficult to assess whether the atrial septal defects observed in the trisomy 16 mouse model 3 and human fetuses with Down syndrome 7 are attributable to impairment of the formation of extracardiac mesenchyme or of endocardium-derived mesenchyme.…”

Section: Discussionmentioning

confidence: 99%

Two Distinct Pools of Mesenchyme Contribute to the Development of the Atrial Septum

Mommersteeg

Soufan

Lange

et al. 2006

Circulation Research

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Closure of the primary atrial foramen is achieved by fusion of the atrioventricular cushions with the mesenchymal cap on the leading edge of the muscular primary atrial septum. A fourth component involved is the vestibular spine, originally described by His in 1880 as an intra-cardiac continuation of the extra-cardiac mesenchyme of the dorsal mesocardium. The morphogenesis of this area is of great clinical interest, because of the high incidence of atrial and atrioventricular septal defects. Nonetheless, the origin of the participating components is largely unknown. Here we report that the primary atrial foramen is surrounded in its entirety by mesenchyme derived from endocardium. A second population of mesenchyme not derived from endocardium was observed at the caudal margin of the mesenchymal atrial cap, entirely embedded within the mesenchyme derived from endocardium and contiguous with the mesenchyme of the dorsal mesocardium. Our reconstructions show this second population does indeed take the form of a short spine, albeit that it is the right pulmonary ridge, rather than this spine, that protrudes into the atrial lumen. From the stance of morphological description, therefore, there is little thus far to substantiate the existence of an atrial spine. It is currently thought that the atrioventricular (AV) cushions, along with the primary atrial septum and the mesenchymal cap carried on its leading edge, are the main contributors to the process of atrial septation. A growing body of evidence points to the involvement of a fourth component, namely the vestibular spine ("spina vestibuli"). [1][2][3][4][5][6][7][8] The vestibular spine was initially nominated as playing such a role in 1880, by Wilhelm His the elder. 9 He described the spine as a triangular mesenchymal wedge, which protruded into the lumen of the atrium from a non-muscular area, which he called the "area interposita," in the dorsal wall of the common atrium ( Figure 1, stippled circle). The spine then disappeared from view for more than a century, eventually being retrieved by several workers, 1,2,4 -6,10,11 albeit with disagreements concerning the form and origin of this tissue. To clarify this, we have performed a lineage study using Tie2-Cre mice 12 to label endocardium and endocardium-derived mesenchyme, in combination with threedimensional reconstructions 13 to permit independent evaluation of the structures involved in atrial septation. Materials and MethodsThe Tie2-Cre and R26R transgenic mouse lines have been described previously. 12,14 Detection of ␤-galactosidase activity and immunohistochemistry were performed on 20-m thick cryostat sections. 15 Non-radioactive in situ hybridization analysis was performed on 12-m thick paraffin sections. 16 Three-dimensional visualization and geometry reconstruction of patterns of gene expression was then achieved. 13,17 Movie clips of these reconstructions are available on request. ResultsAt embryonic day (E) 9.5, it is possible to recognize two ridges, of equal size, at the connection of the dorsal m...

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“…The relationship between septum primum mobility and the presence of atrial extrasystoles was assessed in a study comparing a group of fetuses with atrial extrasystoles and a control group of normal fetuses. The redundancy index (RI), defined as the ratio between septum primum maximal excursion and left atrial maximal diameter on fetal echocardiogram (four-chamber view), showed that septum primum is more redundant in fetuses with atrial extrasystoles during intrauterine life 16 .…”

Section: Discussionmentioning

confidence: 99%

“…In addition to myocytes, there is also the aforementioned presence of mesenchymal tissue in the septum primum [14][15][16] . The septum primum is covered by the endocardium, which is made up of elongated and flattened cells 17 .…”

Section: Introductionmentioning

confidence: 99%