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TPA affects both mesoderm and neural differentiation in aggregates of cultured Xenopus ectoderm cells
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Cell S t a t e S p l i t t e r s Cause P r i m a r y Neural Induction and Differentiation R i c h a r d G o r d o n & G. W a y n e B r o d l a n d The cell state splitter is a mechanically unstable cytoskeletal organelle, (apical microfilament ring with coplanar mat of microtubules) , in e m b r y o n i c ectoderm cells that may cause their differentiation to neural plate and epidermis. Consequences include: I) a m e c h a n i c a l explanation of the binary nature of differentiation; 2) a mechanical explanation of the sharp boundary between neural plate and epidermis (compartmentalization); 3) r e d u c t i o n of positional information to 1-bit (no g r a d i e n t s ) ; 4) a m e c h a n i c a l basis for cell-cell communication (no " m o r p h o g e n s " ) ; 5) a m e c h a n i c a l basis for the epigenetic landscape; 6) a mechanical basis of the action of the organizer and artificial inducers (no "chemical inducer molecule"); 7) t h e notion that the genome responds to this differentiation by producing a repertoire of protein synthesis appropriate to the new mechanical state of the cell, stabilizing the n e w s t a t e ; 8) p o s t u l a t i o n of a state of nuclear competence to respond to a 1-bit signal from the cell.
Abstract not received
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TPA affectsbo~h mesodermand neural differentiationin aggregates of culturedXenopus ectodermcells. M.Heideveld, M.R. Woortman, C.R. Sharpe ~ and A.J. Durston; hi*brechtLaboratory, Uppsalalaan 8, 3584 CT Utrecht, The Netherlands. Cancer Research Campaign Molecular EmbryologyUnit, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.
EXPRESSION OF NEURAL ANTIGENS IN ANIMAL CAP EXPLANTS AND EXOGASTRUIAE OF XENOPUS LAEVIS.
Keiji Itoh and Hiroshi Y. Kubota. Department of Zoology, Faculty of Science, Kyoto University, Kyoto 606, Japan. Animal cap explants (st.10) and exogastrulae of Xenopus laevis were cultured for 3 days. Cellular differentiation in the explants and exogastrulae was examined on serial sections by using monoclonal antibodies specific for neural, epidermal, and somitic tissues. In most cases the animal cap explants expressed only epidermal antigens. However, in a few cases the explants which were excised just above the blastocoel floor expressed neural antigens as well as epidermal antigens but did not express somitic antigens. This indicates either that a small quantity of cells that induce the neural tissue were contained in the explants but they do not differentiate into mesodermal tissues or that neural predetermination has occurred in the cells close to the blastocoel floor. Nearly complete exogastrulae frequently expressed neural antigens in the vegetal region as well as in the equatorial region. The neural tissues were always next to the notochordal and somitic tissues. Based upon these results, the mechanism of neural differentiation will be discussed in relation to the neural induction.
We have analysed the effects of the protein klnase C (PKC) activator 1 2 - O - t e t r a d e c a n o y l ~ h o r b o l - a e e t a t e (TPA) on mesoderm and neural induction in Xenopus. As is k n o w n from the work of Otte et al., (Nature 334, 618-620, 1988), TPA induces competent ectoderm to form neural tisue, therebymimicking the natural,endogenous activation of PKC. This was confirmed and extended in our experiments, using the cell culture system described by Sargent et al., (Devl.Biol.114, 238-246, 1986). TPA t r e a t e d animal c e l l s f a i l e d to express the
posterior central nervous system marker XiHbox 6 (Sharpe, et al., Cell 50, 749-758, 1987), whereas neurofilament RNA (Sharpe; Development 103, 269-277, 1988) was readily detected. We suspect strongly r.hat FKC activation during neural induction is associated with the activation step originally proposed by Nieuwkoop et al., (J.Exp.Zool.120,1-108, 1952). Not only neural ind~ntlonwas found to be affectedby TPA treatment in this cell culture system. Aggregates of animal and vegetal cells, treated(h/ringmesodermal competence, s h o w e d m a s s i v e differentiation to notoehor~ Since isolatedanimal cells did not respond to TPA, we asked w h e t h e r some vegetal c o m p o u n d was
involved. Neither TGFfl, nor FGF ~(imelmam & Kirschner, Cell 51, 869--877,1987) acted synergisticallywith TPA to induce dorsal mesoderm. However, addition of Xenopus XTC conditioned medium (Smith, Development 99, 5-14, 1987) did mimic the action of the putative compov.nd, suggesting that this is a TGF~-llke factor (Rosa et al., Science 239, 785-785, 1988).
$69
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Cell S t a t e S p l i t t e r s Cause P r i m a r y Neural Induction and Differentiation R i c h a r d G o r d o n & G. W a y n e B r o d l a n d The cell state splitter is a mechanically unstable cytoskeletal organelle, (apical microfilament ring with coplanar mat of microtubules) , in e m b r y o n i c ectoderm cells that may cause their differentiation to neural plate and epidermis. Consequences include: I) a m e c h a n i c a l explanation of the binary nature of differentiation; 2) a mechanical explanation of the sharp boundary between neural plate and epidermis (compartmentalization); 3) r e d u c t i o n of positional information to 1-bit (no g r a d i e n t s ) ; 4) a m e c h a n i c a l basis for cell-cell communication (no " m o r p h o g e n s " ) ; 5) a m e c h a n i c a l basis for the epigenetic landscape; 6) a mechanical basis of the action of the organizer and artificial inducers (no "chemical inducer molecule"); 7) t h e notion that the genome responds to this differentiation by producing a repertoire of protein synthesis appropriate to the new mechanical state of the cell, stabilizing the n e w s t a t e ; 8) p o s t u l a t i o n of a state of nuclear competence to respond to a 1-bit signal from the cell.
Abstract not received
213
214
TPA affectsbo~h mesodermand neural differentiationin aggregates of culturedXenopus ectodermcells. M.Heideveld, M.R. Woortman, C.R. Sharpe ~ and A.J. Durston; hi*brechtLaboratory, Uppsalalaan 8, 3584 CT Utrecht, The Netherlands. Cancer Research Campaign Molecular EmbryologyUnit, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.
EXPRESSION OF NEURAL ANTIGENS IN ANIMAL CAP EXPLANTS AND EXOGASTRUIAE OF XENOPUS LAEVIS.
Keiji Itoh and Hiroshi Y. Kubota. Department of Zoology, Faculty of Science, Kyoto University, Kyoto 606, Japan. Animal cap explants (st.10) and exogastrulae of Xenopus laevis were cultured for 3 days. Cellular differentiation in the explants and exogastrulae was examined on serial sections by using monoclonal antibodies specific for neural, epidermal, and somitic tissues. In most cases the animal cap explants expressed only epidermal antigens. However, in a few cases the explants which were excised just above the blastocoel floor expressed neural antigens as well as epidermal antigens but did not express somitic antigens. This indicates either that a small quantity of cells that induce the neural tissue were contained in the explants but they do not differentiate into mesodermal tissues or that neural predetermination has occurred in the cells close to the blastocoel floor. Nearly complete exogastrulae frequently expressed neural antigens in the vegetal region as well as in the equatorial region. The neural tissues were always next to the notochordal and somitic tissues. Based upon these results, the mechanism of neural differentiation will be discussed in relation to the neural induction.
We have analysed the effects of the protein klnase C (PKC) activator 1 2 - O - t e t r a d e c a n o y l ~ h o r b o l - a e e t a t e (TPA) on mesoderm and neural induction in Xenopus. As is k n o w n from the work of Otte et al., (Nature 334, 618-620, 1988), TPA induces competent ectoderm to form neural tisue, therebymimicking the natural,endogenous activation of PKC. This was confirmed and extended in our experiments, using the cell culture system described by Sargent et al., (Devl.Biol.114, 238-246, 1986). TPA t r e a t e d animal c e l l s f a i l e d to express the
posterior central nervous system marker XiHbox 6 (Sharpe, et al., Cell 50, 749-758, 1987), whereas neurofilament RNA (Sharpe; Development 103, 269-277, 1988) was readily detected. We suspect strongly r.hat FKC activation during neural induction is associated with the activation step originally proposed by Nieuwkoop et al., (J.Exp.Zool.120,1-108, 1952). Not only neural ind~ntlonwas found to be affectedby TPA treatment in this cell culture system. Aggregates of animal and vegetal cells, treated(h/ringmesodermal competence, s h o w e d m a s s i v e differentiation to notoehor~ Since isolatedanimal cells did not respond to TPA, we asked w h e t h e r some vegetal c o m p o u n d was
involved. Neither TGFfl, nor FGF ~(imelmam & Kirschner, Cell 51, 869--877,1987) acted synergisticallywith TPA to induce dorsal mesoderm. However, addition of Xenopus XTC conditioned medium (Smith, Development 99, 5-14, 1987) did mimic the action of the putative compov.nd, suggesting that this is a TGF~-llke factor (Rosa et al., Science 239, 785-785, 1988).
$69