Question

You perform the following experiment: Xenopus embryos are treated early in development (before gastrulation begins) with morpholinos to reduce the activity of Cerberus. You take an explant from the dorsal blastopore lip from a normal embryo at the beginning of gastrulation cell movements and inject it into the blastocoel of a normal host embryo. You then take a dorsal blastopore lip explant from a Cerberus 'morphant' (morpholino injected) embryo and transfer it into the blastocoel of a normal host embryo. You observe the effects that the normal explant compared to the Cerberus morphant explant has on the host embryo.

(a) What three signaling pathways are inhibited by Cerberus?

(b) BRIEFLY describe the normal function of Cerberus in patterning the ectoderm? Where is it expressed and what does it do?

(c) Compare the development of the host embryos with the normal blastopore lip inserted into the blastocoel and the host embryo with the Cerberus morphant blastopore lip inserted into the blastocoel.

Answer 1

a) Three major signaling pathways have been shown to be essential in establishing mesodermal pattern, the Wnt/β-catenin, BMP/Smad1 and VegT/Xnr-derriere/Smad 2 pathways.

The Wnt signaling pathway play complex roles in patterning the mesoderm. BMP could induce ventral mesoderm formation. The vegetally localized, maternal T-box transcription factor (VegT) induce ventral, general and dorsal mesoderm by regulating the expression of activin-like TGFβs

b) Cerberus (Cer) is an inhibitor in the TGF-β signaling pathway secreted during the gastrulation phase of embryogenesis. It is a gene that encodes a a secreted signaling protein called cytokine,  important for induction and formation of the heart and head in vertebrates. Mesoderm gives rise to bones, muscles, the heart and circulatory system and internal sex organs.

c) Comparison of the development of the host embryos with the normal blastopore lip inserted into the blastocoel and the host embryo with the Cerberus morphant blastopore lip inserted into the blastocoel.

The region in amphibian embryos where gastrulation begins. Also known as the Spemann–Mangold organizer. In the development of the host embryos with the normal blastopore lip inserted into the blastocoel the dorsal blastopore lip becomes composed of cells that involute into the embryo to become the prechordal plate (the precursor of the head mesoderm). But when the host embryo with the Cerberus morphant blastopore lip inserted into the blastocoel host cells began to participate in the production of the new embryo.