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Vascular pericytes in the chorio-allantois of the chick embryo
0047-7206/82/030367-02503.00/0 Pergamon Press Ltd.
Micron, VoI.13, No.3, pp.367-368, 1982. Printed in Great Britain
V A S C U L A R P E R I C Y T E S IN THE C H O R I O - A L L A N T O I S OF THE C H I C K EMBRYO
Gutta I. Schoefl D e p a r t m e n t of E x p e r i m e n t a l Pathology, The John C u r t i n School of M e d i c a l Research, The A u s t r a l i a n N a t i o n a l University, Canberra, ACT 2601
The d i f f e r e n t i a t i o n of p e r i c y t e s (PC) was e x a m i n e d in the d e v e l o p i n g c i r c u l a t i o n of the chick c h o r i o - a l l a n t o i s (day 7-14). In this tissue, the v a s c u l a r bed d i f f e r e n t i a t e s into two s£rata1: a n e t w o r k of b r a n c h e s in the m e s e n c h y m e and a superficial sinus (SS) that aligns against the c h o r i o n i c e p i t h e l i u m (CE) and u l t i m a t e l y becomes e m b e d d e d in it. The SS is further m o d i f i e d to facilitate e x c h a n g e of r e s p i r a t o r y gases. Its outer surface becomes greatly a t t e n u a t e d and few nuclei (-10%) are p o s i t i o n e d on that side. P r e s u m p t i v e 'adventitial' cells of the 90 h a l l a n t o i c c i r c u l a t i o n 2 and p e r i c y t e s of the fully d i f f e r e n t i a t e d SS 3 have been described. D u r i n g the p e r i o d examined, all b l o o d vessels were a s s o c i a t e d w i t h cells external to the endothelium. Early on, these cells r e s e m b l e d m e s e n c h y m a l cells. Some were c l o s e l y applied to the vessel, even d u r i n g mitosis, others p r o j e c t e d far into the m e s e n c h y m e (Figs. 1,2). A band of fibrils was noted in the c y t o p l a s m facing the vessel. E x c e p t for focal areas of contact, these cells were separated from the e n d o t h e l i u m by an incomplete basal lamina and they were c o a t e d w i t h strands of similar material. D e e p e r vessels were s u r r o u n d e d by them, on the SS, they became r e s t r i c t e d to the m e s e n c h y m a l surface w h e n the sinus aligned against the CE (Figs. 1,2). Their d e v e l o p m e n t d i f f e r e d in these two v a s c u l a r strata. They e v e n t u a l l y formed a sleeve of f l a t t e n e d cells around vessels of the mesenchyme. The c y t o p l a s m became f i b r i l l a r and cell p r o c e s s e s i n t e r d i g i t a t e d w i t h the e n d o t h e l i u m (Fig. 5). PCs a s s o c i a t e d w i t h the SS r e t a i n e d their p o s i t i o n on the lower surface of the sinus when this v a s c u l a r layer was e n g u l f e d by e p i t h e l i a l cells (Fig. 3). Subsequently, they a p p e a r e d to d i m i n i s h in volume or number. Few i n t e r d i g i t a tions w i t h e n d o t h e l i a l cells were seen, c i s t e r n a e of the e n d o p l a s m i c r e t i c u l u m r e m a i n e d p r o m i n e n t and fibrils were limited to a n a r r o w zone (Fig. 4). By day 14, p r o c e s s e s of PCs were i n t e r c a l a t e d b e t w e e n the sinus and the basal layer of the CE (Fig. 6) as r e p o r t e d by Hoshi and Mori 3, they never e x t e n d e d to the outer surface of the sinus. The r e t e n t i o n of p e r i c y t e s on the SS w h e n it becomes e n v e l o p e d by the CE, attests to their u b i q u i t o u s p r e s e n c e in the m i c r o c i r c u l a t i o n . Cell c h a r a c t e r i s t i c s suggest c o n t r a c t i l e ~ and secretory functions. In this circulation, the c l u s t e r i n g of e n d o t h e l i a l nuclei on the lower surface of the SS and c o n c o m i t a n t d i m i n u t i o n of PCs also raise the p o s s i b i l i t y that some of them become i n c o r p o r a t e d into the e n d o t h e l i a l lining. References i. 2. 3. 4.
G.I. Schoefl, Eur. J. Cell Biol. 22:432, 1980 N. Sethi and M. Brookes, J. Anat. 109:1, 1971 H. Hoshi and T. Mori, Arch. histol, jap. 33:45, 1971 R.G. Tilton, C. Kilo, J.R. W i l l i a m s o n and D.W. Murch, Microvasc. 18:336, 1979
367
Res.
368
G. I. Schoef]
A
6 Figs.
1 & 2:
Fig.
3:
Fig.
4:
Fig.
5:
Fig.
6:
S u p e r f i c i a l v a s c u l a r network of the 7 day CAM sampled at the a d v a n c i n g edge (Fig. I) and more p r o x i m a l l y (Fig. 2). P e r i c y t e s (PC) become limited to the m e s e n c h y m a l surface when the network aligns against the chorionic e p i t h e l i u m (CE). Eleven days' incubation. The superficial sinus and a s s o c i a t e d p e r i c y t e s become e m b e d d e d in the c h o r i o n i c e p i t h e l i u m (CE). P e r i c y t e i n t e r c a l a t e d b e t w e e n the e n d o t h e l i u m of the superficial sinus and the basal c h o r i o n i c e p i t h e l i u m (CE). From a vessel in the m e s e n c h y m e i l l u s t r a t i n g i n t e r d i g i t a t i o n s of p e r i c y t e s with e n d o t h e l i a l cells. C h o r i o n i c e p i t h e l i u m w i t h superficial sinus on day 14.
Micron, VoI.13, No.3, pp.367-368, 1982. Printed in Great Britain
V A S C U L A R P E R I C Y T E S IN THE C H O R I O - A L L A N T O I S OF THE C H I C K EMBRYO
Gutta I. Schoefl D e p a r t m e n t of E x p e r i m e n t a l Pathology, The John C u r t i n School of M e d i c a l Research, The A u s t r a l i a n N a t i o n a l University, Canberra, ACT 2601
The d i f f e r e n t i a t i o n of p e r i c y t e s (PC) was e x a m i n e d in the d e v e l o p i n g c i r c u l a t i o n of the chick c h o r i o - a l l a n t o i s (day 7-14). In this tissue, the v a s c u l a r bed d i f f e r e n t i a t e s into two s£rata1: a n e t w o r k of b r a n c h e s in the m e s e n c h y m e and a superficial sinus (SS) that aligns against the c h o r i o n i c e p i t h e l i u m (CE) and u l t i m a t e l y becomes e m b e d d e d in it. The SS is further m o d i f i e d to facilitate e x c h a n g e of r e s p i r a t o r y gases. Its outer surface becomes greatly a t t e n u a t e d and few nuclei (-10%) are p o s i t i o n e d on that side. P r e s u m p t i v e 'adventitial' cells of the 90 h a l l a n t o i c c i r c u l a t i o n 2 and p e r i c y t e s of the fully d i f f e r e n t i a t e d SS 3 have been described. D u r i n g the p e r i o d examined, all b l o o d vessels were a s s o c i a t e d w i t h cells external to the endothelium. Early on, these cells r e s e m b l e d m e s e n c h y m a l cells. Some were c l o s e l y applied to the vessel, even d u r i n g mitosis, others p r o j e c t e d far into the m e s e n c h y m e (Figs. 1,2). A band of fibrils was noted in the c y t o p l a s m facing the vessel. E x c e p t for focal areas of contact, these cells were separated from the e n d o t h e l i u m by an incomplete basal lamina and they were c o a t e d w i t h strands of similar material. D e e p e r vessels were s u r r o u n d e d by them, on the SS, they became r e s t r i c t e d to the m e s e n c h y m a l surface w h e n the sinus aligned against the CE (Figs. 1,2). Their d e v e l o p m e n t d i f f e r e d in these two v a s c u l a r strata. They e v e n t u a l l y formed a sleeve of f l a t t e n e d cells around vessels of the mesenchyme. The c y t o p l a s m became f i b r i l l a r and cell p r o c e s s e s i n t e r d i g i t a t e d w i t h the e n d o t h e l i u m (Fig. 5). PCs a s s o c i a t e d w i t h the SS r e t a i n e d their p o s i t i o n on the lower surface of the sinus when this v a s c u l a r layer was e n g u l f e d by e p i t h e l i a l cells (Fig. 3). Subsequently, they a p p e a r e d to d i m i n i s h in volume or number. Few i n t e r d i g i t a tions w i t h e n d o t h e l i a l cells were seen, c i s t e r n a e of the e n d o p l a s m i c r e t i c u l u m r e m a i n e d p r o m i n e n t and fibrils were limited to a n a r r o w zone (Fig. 4). By day 14, p r o c e s s e s of PCs were i n t e r c a l a t e d b e t w e e n the sinus and the basal layer of the CE (Fig. 6) as r e p o r t e d by Hoshi and Mori 3, they never e x t e n d e d to the outer surface of the sinus. The r e t e n t i o n of p e r i c y t e s on the SS w h e n it becomes e n v e l o p e d by the CE, attests to their u b i q u i t o u s p r e s e n c e in the m i c r o c i r c u l a t i o n . Cell c h a r a c t e r i s t i c s suggest c o n t r a c t i l e ~ and secretory functions. In this circulation, the c l u s t e r i n g of e n d o t h e l i a l nuclei on the lower surface of the SS and c o n c o m i t a n t d i m i n u t i o n of PCs also raise the p o s s i b i l i t y that some of them become i n c o r p o r a t e d into the e n d o t h e l i a l lining. References i. 2. 3. 4.
G.I. Schoefl, Eur. J. Cell Biol. 22:432, 1980 N. Sethi and M. Brookes, J. Anat. 109:1, 1971 H. Hoshi and T. Mori, Arch. histol, jap. 33:45, 1971 R.G. Tilton, C. Kilo, J.R. W i l l i a m s o n and D.W. Murch, Microvasc. 18:336, 1979
367
Res.
368
G. I. Schoef]
A
6 Figs.
1 & 2:
Fig.
3:
Fig.
4:
Fig.
5:
Fig.
6:
S u p e r f i c i a l v a s c u l a r network of the 7 day CAM sampled at the a d v a n c i n g edge (Fig. I) and more p r o x i m a l l y (Fig. 2). P e r i c y t e s (PC) become limited to the m e s e n c h y m a l surface when the network aligns against the chorionic e p i t h e l i u m (CE). Eleven days' incubation. The superficial sinus and a s s o c i a t e d p e r i c y t e s become e m b e d d e d in the c h o r i o n i c e p i t h e l i u m (CE). P e r i c y t e i n t e r c a l a t e d b e t w e e n the e n d o t h e l i u m of the superficial sinus and the basal c h o r i o n i c e p i t h e l i u m (CE). From a vessel in the m e s e n c h y m e i l l u s t r a t i n g i n t e r d i g i t a t i o n s of p e r i c y t e s with e n d o t h e l i a l cells. C h o r i o n i c e p i t h e l i u m w i t h superficial sinus on day 14.