Dissection of a Krox20 positive feedback loop driving cell fate choices in hindbrain patterning.
Although feedback loops are essential in development, their molecular implementation and precise functions remain elusive. Using enhancer knockout in mice, we demonstrate that a direct, positive autoregulatory loop amplifies and maintains the expression of Krox20, a transcription factor governing vertebrate hindbrain segmentation. By combining quantitative data collected in the zebrafish with biophysical modelling that accounts for the intrinsic stochastic molecular dynamics, we dissect the loop at the molecular level. We find that it underpins a bistable switch that turns a transient input signal into cell fate commitment, as we observe in single cell analyses. The stochasticity of the activation process leads to a graded input-output response until saturation is reached. Consequently, the duration and strength of the input signal controls the size of the hindbrain segments by modulating the distribution between the two cell fates. Moreover, segment formation is buffered from severe variations in input level. Finally, the progressive extinction of Krox20 expression involves a destabilization of the loop by repressor molecules. These mechanisms are of general significance for cell type specification and tissue patterning.
1] Ecole Normale Supérieure, IBENS, Paris, France [2] INSERM, U1024, Paris, France [3] CNRS, UMR 8197, Paris, France.
Yassine X
YX
Bouchoucha
Jürgen
J
Reingruber
Charlotte
C
Labalette
Michel A
MA
Wassef
Elodie
E
Thierion
Carole
C
Desmarquet-Trin Dinh
David
D
Holcman
Pascale
P
Gilardi-Hebenstreit
Patrick
P
Charnay
D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D019521:Body Patterning / Q000235:genetics*; D002454:Cell Differentiation; D049109:Cell Proliferation; D002642:Chick Embryo; D051766:Early Growth Response Protein 1 / Q000235:genetics* / Q000378:metabolism; D051767:Early Growth Response Protein 2 / Q000235:genetics* / Q000378:metabolism; D004622:Embryo, Mammalian; D004625:Embryo, Nonmammalian; D004742:Enhancer Elements, Genetic; D025461:Feedback, Physiological; D018507:Gene Expression Regulation, Developmental; D017403:In Situ Hybridization; D051379:Mice; D008969:Molecular Sequence Data; D012249:Rhombencephalon / Q000166:cytology* / Q000254:growth & development / Q000378:metabolism; D015398:Signal Transduction; D013269:Stochastic Processes; D014158:Transcription, Genetic; D015027:Zebrafish
D051766:Early Growth Response Protein 1; D051767:Early Growth Response Protein 2; C486109:Egr1 protein, mouse