The topic of this website is the patterning of the dorso-ventral axis in Xenopus. Development into a multicellular organism is the most complicated fate a single cell can undergo. Genes control development by controlling when and where proteins are synthesised. Cell-cell interactions determine how the embryo develops.  

image courtesy of Wiki commons under creative commons licence.

Overview of Xenopus development

Cleavage in the Xenopus egg occurs about 90 minutes after fertilisation and is along the plane of the animal-vegetal axis, dividing the embryo into equal left and right halves. Further cleavages occur at intervals of about 20 minutes.

The egg is split into four animal cells and four larger vegetal cells. There is no cell growth during this early division, so smaller cells are formed. The cells deriving from cleavage division are known as blastomeres. Inside this spherical mass of cells is a fluid filled cavity known as a blastocoel. The embryo is now called a blastula.

The next stage is gastrulation. This is a phase in the early development of the embryo whereby the cells of the blastocyst are translocated to establish the three germ layers:

Ectoderm

This is a germ layer that gives rise to the epidermis and the nervous system.

Endoderm

This germ layer gives rise to gut and associated organs, such as lungs and liver in vertebrates.

Mesoderm

This germ layer gives rise to the skeleto-muscular system, connective tissues, the blood and internal organs such as the kidney and heart.

During gastrulation, embryonic cells migrate through an opening within the embryo known as the blastocoele. As the gastrula forms, the remnants of the blastocoele shrink to eventually disappear completely.

Gastrulation is followed by organogenesis, when individual organs develop within the newly formed germ layers.