EPIDERMAL DEVELOPMENT AND THE DLL-A/B CLUSTER

The Dll-A/Dll-B bi-gene cluster of the model chordate Ciona intestinalis is one of the most compact and organizationally simple examples of a developmental gene cluster known. While some of the regulatory interactions within gene clusters have been analyzed, the simple Dll-A/Dll-B cluster in C. intestinalis offers an opportunity to obtain a more complete picture of the coordinated regulatory architecture of a whole developmental gene cluster. Using a combination of transgenic reporter assays and gene expression studies by in-situ hybridization, we are analyzing how genomic regulatory elements hard-wired into the DNA control the expression of the two genes in the cluster.

Expression of a reporter transgene with lacZ inserted into the DllA-B gene cluster in Ciona intestinalis.

Apart from its interesting genomic organization, Dll-B is a pivotal gene in the transcriptional control network responsible for specification and morphogenesis of the epidermis, the organ that mediates the interface between the animal and its environment. We are studying the function of Dll-B and its interactions with other genes using transgenic methods to misexpress or overexpress the gene and look for effects on possible target genes. We are also looking for upstream regulators of Dll-B by analyzing candidates that might bind or otherwise interact with the DllA-B cluster regulatory DNA.

Ciona embryo with transgenic misexpression of Dll-B in non-epidermal cells showing clumping of normally linear array of notochord cells (labelled with a Ci-bra reporter gene).

EVOLUTION OF TRANSCRIPTIONAL REGULATORY ELEMENTS

Much of the action in morphological evolution can be traced to genomic regulatory elements in the DNA that control transcription, or where and when genes are "turned on". We are examining the evolutionary differences between these regulatory elements for the same gene in different species of ascidians. We have dissected the GREs in the Pax6 gene of Ciona and are comparing them to GREs found in the same gene in other species of ascidians.

Ocellus Pax6 enhancer reporter gene expression