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Vasculogenesis, angiogenesis and haemopoiesis during avian ontogeny
726
725
The organization of the azygos vein arch was studied in human embryos measuring 5 to 31 mm in C-R length, and a new theory was develo ped to explain the formation of the pulmonary azygos lobe. The azygos vein system is organized during O'Rahilly's stages 18 and 19 from the supracar dinal or sympathomedial veins together with the persistent proximal segment of the poste riot cardinal vein. This latter gives rise to the entire segment designated the azygos vein arch. An azygos pulmonary lobe is formed only when a long thoracic segment of the right pos terior cardinal vein persists beyond O'Rahilly's stage 18, as a result of the fai lure of the ipsilateral supracardinal or sym pathomedial vein to form. This implies that the underlying origin of the pulmonary azygos lobe is the morphogenetic failure of the azy gos vein system, while the immediate cause is the persistence of the thoracic segment of the right posterior cardinal vein. Thus the abnormal pulmonary lobe would be more accura tely termed pseudolobe of the persistent pos terior cardinal vein
ORIGINS AND ASSEMBLY OF AVIAN CRANIOFACIAL BLOOD VESSSLS D. M. Noden, Department of Anatomy, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA, 14853 The descriptive studies of Sabin clearly showed that endothelial cells arise by two processes: budding and branching from pre-existing vessels (i.e. angiogenesis), and local aggregation of angioblasts to form vesicles thee fuse with these branches. The origins of these local angloblasts and the mechanisms by which they assemble into blood vessels remain controversial. To resolve these problems, quail tissues were implanted in chick hosts prior to the onset of embryonic vasculogenesis. Several days later these chimeras were fixed and sectioned, then polyclonal antibodies specific for quail endothelial cells were applied to the sections. Paraxial mesoderm from all axial levels were found to conLain endogenous angioblasts; other embryonic tissues lack these committed precursors. Angioblasts emigrate in all directions from the implant and move invasively through adjacent mesenchyme. The vascular system in chimeric embryos was reconstructed and found to be normal, regardless of the original source of endothelial cells. Thus, most intra-embryonic mesoderm contains committed angioblasts that exhibit an extensive, highly invasive mode of cell movement. This process bdngs about a massive rearrangement of angicblasts, including their movement into non-angiogenic mesenchyme. Assembly of blood vessels is under the control of local connective tissueforming mesenchyme, similar to the assembly of muscles and peripheral nerves. Supported by NIH grant DE06632 from NIDR.
727
728
Organization of the Pulmonary Azygos Lobe M6rJda, J.A.; Espfn, J.; Garcfa, S.
Vasculogenesis, angiogenesis haemopoiesis during avian ontogeny.
and
Epiboly, Germ Layer and Axis Formation in Brachydanio (Zebrafish}
L. Pardanaud, F. Yassine & F. Dieterlcn-Li~vre.
F l e i g , R . , V o l l m a r , H . & S a n d e r , K . , Inst. Biol. I, A l b e r t s t r . 2 1 a , D - 7 8 0 0 F r e i b u r g
Institut d'Embryologie du CNRS et du Col/dge de France, 94130 Nogent sur Marne, France.
Time Lapse films taken with DIC optical s e c t i o n i n g s h o w t h a t in the z e b r a f i s h the d e e p c e l l s - c o n t r a r y to e a r l i e r v i e w s ( S a n d e r et al. J E E M 82 s u p p l . : 2 1 4 , 1984) t u r n i n w a r d as in the r o s y b a r b (Wood & T i m m e r m a n s , D e v e l o p m e n t 1 0 2 : 5 7 5 , 1 9 8 8 ) . S c a n n i n g EM p r e p a r a t i o n s r e v e a l t h a t the i n t e r n a l ized deep cells separate into a mesod e r m a l p o p u l a t i o n m a i n l y a t t a c h e d to the o u t e r ( = e c t o d e r m a l ) d e e p c e l l layer, a n d i n d i v i d u a l e n d o d e r m a l c e l l s m o v i n g on the y o l k s y n c y t i a l l a y e r . T h e c e l l s of b o t h g e r m l a y e r s g r a d u a l l y f l a t t e n a n d b e c o m e m u l t i p o l a r as t h e y a p p r o a c h the f u t u r e b o d y a x i s w h i l e in the b e g i n n i n g t h e y a r e m a i n ly p e a r - s h a p e d w i t h p s e u d o p o d i a e x t e n d i n g f r o m the s i n g l e tip. T h e n e u r a l s t r a n d o r i g i n a t e s f r o m the e c t o d e r m a l l a y e r a d j a c e n t to the n o t o c h o r d a n l a g e formed earlier from mesodermal cells; t h u s no c o m m o n p r e c u r s o r (axial s t r a n d ) e x i s t s for t h e s e two s t r u c t u r e s , t h a t a l s o s h o w p a r t i a l i n d e p e n d e n c e in m a l f o r m e d e m b r y o s ( B a u m a n n & S a n d e r , J. exp. Zool. 2 3 0 : 3 6 3 , 1 9 8 4 ) .
Two processes of vascularization could be distinguished during avian ontogeny. Endothelial cells differentiated either in situ (vasculogenesis) or through an invasion process (angiogenesis). Which process occurred depended on the origin of the mesodermal layer, i.e., whether it was splanchnopleural or somatopleural. This study was realized by means of quail-chick interspecific grafts and the endothelial cells were recognized with monoclonal antibody QH1 which is specific for the quail hemangioblastic lineage. Rudiments of internal organs (mesoderm + endoderm) were vascularized through vasculogenesis; somatopleural rudiments (mesoderm + ectoderm) were invaded bY extrinsic endothelial cells through an angiogenic process. In both cases, the haemopoietic cells were extrinsic. We put forward the hypothesis that endoderm induces the emergence of endothelial cells in the associated mesoderm.
$216
725
The organization of the azygos vein arch was studied in human embryos measuring 5 to 31 mm in C-R length, and a new theory was develo ped to explain the formation of the pulmonary azygos lobe. The azygos vein system is organized during O'Rahilly's stages 18 and 19 from the supracar dinal or sympathomedial veins together with the persistent proximal segment of the poste riot cardinal vein. This latter gives rise to the entire segment designated the azygos vein arch. An azygos pulmonary lobe is formed only when a long thoracic segment of the right pos terior cardinal vein persists beyond O'Rahilly's stage 18, as a result of the fai lure of the ipsilateral supracardinal or sym pathomedial vein to form. This implies that the underlying origin of the pulmonary azygos lobe is the morphogenetic failure of the azy gos vein system, while the immediate cause is the persistence of the thoracic segment of the right posterior cardinal vein. Thus the abnormal pulmonary lobe would be more accura tely termed pseudolobe of the persistent pos terior cardinal vein
ORIGINS AND ASSEMBLY OF AVIAN CRANIOFACIAL BLOOD VESSSLS D. M. Noden, Department of Anatomy, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA, 14853 The descriptive studies of Sabin clearly showed that endothelial cells arise by two processes: budding and branching from pre-existing vessels (i.e. angiogenesis), and local aggregation of angioblasts to form vesicles thee fuse with these branches. The origins of these local angloblasts and the mechanisms by which they assemble into blood vessels remain controversial. To resolve these problems, quail tissues were implanted in chick hosts prior to the onset of embryonic vasculogenesis. Several days later these chimeras were fixed and sectioned, then polyclonal antibodies specific for quail endothelial cells were applied to the sections. Paraxial mesoderm from all axial levels were found to conLain endogenous angioblasts; other embryonic tissues lack these committed precursors. Angioblasts emigrate in all directions from the implant and move invasively through adjacent mesenchyme. The vascular system in chimeric embryos was reconstructed and found to be normal, regardless of the original source of endothelial cells. Thus, most intra-embryonic mesoderm contains committed angioblasts that exhibit an extensive, highly invasive mode of cell movement. This process bdngs about a massive rearrangement of angicblasts, including their movement into non-angiogenic mesenchyme. Assembly of blood vessels is under the control of local connective tissueforming mesenchyme, similar to the assembly of muscles and peripheral nerves. Supported by NIH grant DE06632 from NIDR.
727
728
Organization of the Pulmonary Azygos Lobe M6rJda, J.A.; Espfn, J.; Garcfa, S.
Vasculogenesis, angiogenesis haemopoiesis during avian ontogeny.
and
Epiboly, Germ Layer and Axis Formation in Brachydanio (Zebrafish}
L. Pardanaud, F. Yassine & F. Dieterlcn-Li~vre.
F l e i g , R . , V o l l m a r , H . & S a n d e r , K . , Inst. Biol. I, A l b e r t s t r . 2 1 a , D - 7 8 0 0 F r e i b u r g
Institut d'Embryologie du CNRS et du Col/dge de France, 94130 Nogent sur Marne, France.
Time Lapse films taken with DIC optical s e c t i o n i n g s h o w t h a t in the z e b r a f i s h the d e e p c e l l s - c o n t r a r y to e a r l i e r v i e w s ( S a n d e r et al. J E E M 82 s u p p l . : 2 1 4 , 1984) t u r n i n w a r d as in the r o s y b a r b (Wood & T i m m e r m a n s , D e v e l o p m e n t 1 0 2 : 5 7 5 , 1 9 8 8 ) . S c a n n i n g EM p r e p a r a t i o n s r e v e a l t h a t the i n t e r n a l ized deep cells separate into a mesod e r m a l p o p u l a t i o n m a i n l y a t t a c h e d to the o u t e r ( = e c t o d e r m a l ) d e e p c e l l layer, a n d i n d i v i d u a l e n d o d e r m a l c e l l s m o v i n g on the y o l k s y n c y t i a l l a y e r . T h e c e l l s of b o t h g e r m l a y e r s g r a d u a l l y f l a t t e n a n d b e c o m e m u l t i p o l a r as t h e y a p p r o a c h the f u t u r e b o d y a x i s w h i l e in the b e g i n n i n g t h e y a r e m a i n ly p e a r - s h a p e d w i t h p s e u d o p o d i a e x t e n d i n g f r o m the s i n g l e tip. T h e n e u r a l s t r a n d o r i g i n a t e s f r o m the e c t o d e r m a l l a y e r a d j a c e n t to the n o t o c h o r d a n l a g e formed earlier from mesodermal cells; t h u s no c o m m o n p r e c u r s o r (axial s t r a n d ) e x i s t s for t h e s e two s t r u c t u r e s , t h a t a l s o s h o w p a r t i a l i n d e p e n d e n c e in m a l f o r m e d e m b r y o s ( B a u m a n n & S a n d e r , J. exp. Zool. 2 3 0 : 3 6 3 , 1 9 8 4 ) .
Two processes of vascularization could be distinguished during avian ontogeny. Endothelial cells differentiated either in situ (vasculogenesis) or through an invasion process (angiogenesis). Which process occurred depended on the origin of the mesodermal layer, i.e., whether it was splanchnopleural or somatopleural. This study was realized by means of quail-chick interspecific grafts and the endothelial cells were recognized with monoclonal antibody QH1 which is specific for the quail hemangioblastic lineage. Rudiments of internal organs (mesoderm + endoderm) were vascularized through vasculogenesis; somatopleural rudiments (mesoderm + ectoderm) were invaded bY extrinsic endothelial cells through an angiogenic process. In both cases, the haemopoietic cells were extrinsic. We put forward the hypothesis that endoderm induces the emergence of endothelial cells in the associated mesoderm.
$216