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Misexpression of chick Vg1 in the marginal zone induces primitive streak formation
S B Shah1, I Skromne, C R Hume
1Department of Physiology and Cellular Biophysics, College of Physicians and Surgeons of Columbia University, New York, NY 10032, USA.
Insights
Chick Vg1 (cVg1) protein, a TGF-beta signaling molecule, is expressed in the posterior marginal zone and can induce secondary primitive streak formation and ectopic embryos in chick embryos.
Area of Science:
- Developmental Biology
- Molecular Embryology
Background:
- The primitive streak is the initial axial structure in chick embryo development.
- Formation is influenced by the posterior marginal zone (PMZ).
Purpose of the Study:
- Investigate the role of chick Vg1 (cVg1) in primitive streak formation.
- Determine if cVg1 can induce ectopic axis formation.
Main Methods:
- Examined cVg1 expression in prestreak chick embryos.
- Induced ectopic cVg1 expression in blastoderms.
- Utilized cell marking techniques.
- Performed in vitro explant assays.
Main Results:
- cVg1 is expressed in the PMZ of prestreak embryos.
- Ectopic cVg1 expression induced secondary primitive streaks and ectopic embryos.
- Cells contributing to ectopic streaks changed fate, exhibiting primitive streak characteristics.
- In vitro exposure to cVg1 induced axial mesodermal properties in epiblast explants.
Conclusions:
- cVg1 mediates ectopic axis formation in chick embryos.
- cVg1 induces new cell fates during primitive streak formation.
- This study allows analysis of primitive streak formation events.
Abstract:
In the chick embryo, the primitive streak is the first axial structure to develop. The initiation of primitive streak formation in the posterior area pellucida is influenced by the adjacent posterior marginal zone (PMZ). We show here that chick Vg1 (cVg1), a member of the TGFbeta family of signalling molecules whose homolog in Xenopus is implicated in mesoderm induction, is expressed in the PMZ of prestreak embryos. Ectopic expression of cVg1 protein in the marginal zone chick blastoderms directs the formation of a secondary primitive streak, which subsequently develops into an ectopic embryo. We have used cell marking techniques to show that cells that contribute to the ectopic primitive streak change fate, acquiring two distinct properties of primitive streak cells, defined by gene expression and cell movements. Furthermore, naive epiblast explants exposed to cVg1 protein in vitro acquire axial mesodermal properties. Together, these results show that cVg1 can mediate ectopic axis formation in the chick by inducing new cell fates and they permit the analysis of distinct events that occur during primitive streak formation.