TITLE:

LATE SPECIFICATION OF THE LARVAL PERIPHERAL NERVOUS SYSTEM IN THE ASCIDIAN CIONA INTESTINALIS (No. 76)

DATE:

Friday, April 8th, 2005

TIME:

3:30 PM

LOCATION:

GMCS 214

SPEAKER:

Robert Zeller, Department of Biology, San Diego State University

ABSTRACT:

The ascidian larval peripheral nervous system (PNS) consists of a series of ciliated cells, called epidermal sensory neurons (ESNs), which are located along the dorsal and ventral midlines of the larval tail and on the dorsal and anterior trunk. Our laboratory is interested in deciphering the gene regulatory network (GRN) that operates during embryogenesis to specify the ESNs. GRNs describe the functional relationships between regulatory genes � genes that encode transcription factors and signal transduction molecules. In the first part of my talk, I will describe GRNs and the way in which they are assayed, in vivo, during embryogenesis. In the second part of my talk, I will summarize recent work in our laboratory to identify key molecules of the PNS GRN and describe the approaches we are taking to understand the functional relationships of these molecules. These approaches include comparative genomics and bioinformatics, microarray analysis, and manipulation of gene function, in vivo. To date, we have identified and characterized a number of regulatory genes from Ciona intestinalis that are involved in later aspects of PNS specification. We propose a model in which one or more Atonal-related transcription factor genes are expressed in broad stripes along the midline of the dorsal and ventral tail epidermis. Lateral inhibition mechanisms, regulated by Notch-Delta signaling, then select certain midline cell for the PNS fate while the remaining cells become epidermis. After selection, the ESN cells express genes encoding two additional transcription factors Рa different Atonal-related gene and a Pou-IV class gene. Ectopic expression of a dominant-negative Suppressor of Hairless gene throughout the embryonic epidermis disrupts Notch-Delta lateral inhibition resulting in the appearance of supernumary ESNs, but only along the dorsal and ventral midlines. Ectopic expression of the Atonal-related genes in the epidermis also produces supernumary ESNs along the dorsal and ventral midlines and additionally in the lateral epidermis where ESNs are not normally produced. This suggests that the domain of Notch-Delta signaling has expanded beyond the midline epidermis into epidermal territories that never give rise to ESNs in wild-type embryos.

HOST:

Faramarz Valafar

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