One of the main interests of our group is understanding the molecular events responsible for mesoderm formation and patterning. In particular we are investigating the role of fibroblast growth factor (FGF) signalling during mesoderm formation in the frog, Xenopus. We have shown that inhibiting FGF signalling during gastrulation disrupts mesoderm specification and morphogenesis. In order to better understand these processes, we have begun to isolate downstream targets of FGF signalling. We have identified Xsprouty2 as an important target gene. This protein and the related proteins, Xsprouty1, Xspred1 and Xspred2 are both targets and modulators of FGF signalling. We have recently shown that the Sprouty and Spred proteins play an important role in FGF signal interpretation, allowing mesoderm specification and morphogenesis to occur in a coordinated fashion.

Cranial nerves revealed in a transgenic stage-47 tadpole expressing placental alkaline phosphatase (PLAP) from the neural specific beta-tubulin promoter.

In order to identify additional genes involved in mesoderm specification and morphogenesis, we are using bioinformatics tools in combination with functional screens to identify additional genes involved in these processes. As part of this project we have identified around 7000 full-length clones from Xenopus tropicalis and have screened nearly 2000 of these clones for genes affecting mesoderm formation and/or morphogenesis. Of those tested, we have isolated 82 genes, which alter or inhibit mesoderm formation and/or gastrulation movements.

In addition we are investigating the role of a novel D-type cyclin during the specification and maintenance of the motor neuron and interneuron precursors within the spinal chord of Xenopus. We are also studying the development of primitive myeloid cells, which give rise to the embryonic macrophages. Furthermore we are investigating their migratory behaviour, especially their recruitment to embryonic wound sites. Finally, we have begun to investigate the genes involved in the development and regeneration of the vasculature in Xenopus.

Trigeminal nerve in a transgenic stage-28 tadpole expressing placental alkaline phosphatase (PLAP) from the neural specific beta-tubulin promoter.

Primitive myeloid cells (dark spots) are present throughout the tailbud stage embryo. These three images are of the same embryo; the one on the left shows the right side of the embryo, the middle image shows the left side of the embryo, and the image on the right is a magnification of the area outlined in the middle image, where the primitive myeloid cells have congregated around an embryonic wound.

Recent publications:

Amaya E (2005) Xenomics. Genome Research 15:1683–1691.

Sivak JM, Petersen L and Amaya E (2005) FGF Signal interpretation is directed by Sprouty and Spred proteins during mesoderm formation. Developmental Cell 8, 689-701

Chen J-A, Voigt J, Gilchrist M, Papalopulu N and Amaya E (2005) Identification of novel genes affecting mesoderm formation and morphogenesis through an enhanced large-scale functional screen in Xenopus. Mechanisms of Development 122, 307-331

Gilchrist M, Zorn AM, Smith JC, Voigt J, Papalopulu N and Amaya E (2004) Defining a large set of full length clones from a Xenopus tropicalis EST project. Dev Biol 271, 498-516

Voigt J, Chen J-A, Gilchrist M, Amaya E and Papalopulu N (2005) Expression cloning screening of a unique and full-length set of cDNA clones is an efficient method for identifying genes involved in Xenopus neurogenesis. Mechanisms of Development 122, 289-306

A montage of embryos showing the expression pattern of a select group of genes isolated in a large-scale gain of function screen aimed at identifying genes able to alter the specification and/or morphogenesis of the mesoderm. The top row shows embryos at the gastrula stages, the next two rows show embryos at the neurula stages and the bottom four rows show embryos at the tailbud stages.

Cross sections of the spinal cord of Xenopus tadpoles stained for the expression of different markers along the dorso-ventral axis.