Single cells can sense their position in a morphogen gradient.
Xenopus blastula cells show a morphogen-like response to activin by expressing different genes according to the concentration of activin to which they are exposed. To understand how cells recognize their position in a concentration gradient, it is essential to know whether each cell responds individually to activin concentration. An alternative idea, proposed by previous work, is that cells need to interact with their neighbours to generate a concentration-related response. To distinguish between these ideas, we have cultured blastula cells under conditions which provide different degrees of contact with other cells, allowing nil to maximum communication with their neighbours. The cultures include cells attached to fibronectin and cells resting unattached on an agarose base. The cultures also include cells that have no contact with any cell except their clonal progeny, cells that have lateral contact to neighbouring cells, and cells that are completely enveloped by other cells in a reaggregate. We have used RNase protection and in situ hybridization to assay the expression of the activin-responsive Xenopus genes Xbra, Xgsc, Xeomes, Xapod, Xchordin, Mix1, Xlim1 and Cerberus. We find no difference in gene expression between cells attached to fibronectin and those unattached on agarose. Most importantly, we find that cells respond to activin in a concentration-related way irrespective of their degree of contact with other cells. Therefore interaction among cells is not required for the interpretation of morphogen concentration, at least in the case of the early genes studied here. We conclude that isolated blastula cells can sense and respond individually to activin by expressing genes in a concentration-dependent way.
Gurdon
J B
JB
Wellcome CRC Institute, Tennis Court Road, Cambridge CB2 1QR and Department of Zoology, University of Cambridge, UK. jbg1000@hermes.cam.ac.uk
Standley
H
H
Dyson
S
S
Butler
K
K
Langon
T
T
Ryan
K
K
Stennard
F
F
Shimizu
K
K
Zorn
A
A
D028341:Activins; D000818:Animals; D001757:Blastomeres / Q000166:cytology* / Q000187:drug effects; D002450:Cell Communication / Q000187:drug effects; D019070:Cell Lineage; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004625:Embryo, Nonmammalian / Q000166:cytology; D005786:Gene Expression Regulation / Q000187:drug effects*; D006023:Glycoproteins; D051956:Goosecoid Protein; D018398:Homeodomain Proteins / Q000187:drug effects / Q000235:genetics; D017403:In Situ Hybridization; D007265:Inhibins / Q000494:pharmacology*; D036341:Intercellular Signaling Peptides and Proteins; D060850:LIM-Homeodomain Proteins; D011506:Proteins / Q000187:drug effects / Q000235:genetics; D017468:Receptors, Fibroblast Growth Factor / Q000187:drug effects / Q000235:genetics; D012097:Repressor Proteins; D012260:Ribonucleases / Q000235:genetics / Q000378:metabolism; D020825:T-Box Domain Proteins / Q000235:genetics; D014157:Transcription Factors; D014981:Xenopus / Q000196:embryology*; D029867:Xenopus Proteins
C103223:EOMES protein, Xenopus; D006023:Glycoproteins; D051956:Goosecoid Protein; D018398:Homeodomain Proteins; D036341:Intercellular Signaling Peptides and Proteins; D060850:LIM-Homeodomain Proteins; C543964:Lhx1 protein, Xenopus; C100368:Mix1 protein, Xenopus; D011506:Proteins; D017468:Receptors, Fibroblast Growth Factor; D012097:Repressor Proteins; D020825:T-Box Domain Proteins; C116765:TBXT protein, Xenopus; D014157:Transcription Factors; C103966:VegT protein, Xenopus; D029867:Xenopus Proteins; C100866:cer1 protein, Xenopus; D028341:Activins; D007265:Inhibins; C054234:chordin; D012260:Ribonucleases