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Molecular and Cellular Biology, June 2009, p. 3390-3400, Vol. 29, No. 12
0270-7306/09/$08.00+0     doi:10.1128/MCB.01764-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

The Cell Surface Receptor Tartan Is a Potential In Vivo Substrate for the Receptor Tyrosine Phosphatase Ptp52F{triangledown} ,{dagger}

Lakshmi Bugga,1,{ddagger} Anuradha Ratnaparkhi,1,2 and Kai Zinn1*

Division of Biology, California Institute of Technology, Pasadena, California 91125,1 Agharkar Research Institute, Animal Sciences Division (Zoology), G. G. Agharkar Road, Pune 411004, India2

Received 18 November 2008/ Returned for modification 2 January 2009/ Accepted 19 March 2009

Receptor-linked protein-tyrosine phosphatases (RPTPs) are essential regulators of axon guidance and synaptogenesis in Drosophila, but the signaling pathways in which they function are poorly defined. We identified the cell surface receptor Tartan (Trn) as a candidate substrate for the neuronal RPTP Ptp52F by using a modified two-hybrid screen with a substrate-trapping mutant of Ptp52F as "bait." Trn can bind to the Ptp52F substrate-trapping mutant in transfected Drosophila S2 cells if v-Src kinase, which phosphorylates Trn, is also expressed. Coexpression of wild-type Ptp52F causes dephosphorylation of v-Src-phosphorylated Trn. To examine the specificity of the interaction in vitro, we incubated Ptp52F-glutathione S-transferase (GST) fusion proteins with pervanadate-treated S2 cell lysates. Wild-type Ptp52F dephosphorylated Trn, as well as most other bands in the lysate. GST "pulldown" experiments demonstrated that the Ptp52F substrate-trapping mutant binds exclusively to phospho-Trn. Wild-type Ptp52F pulled down dephosphorylated Trn, suggesting that it forms a stable Ptp52F-Trn complex that persists after substrate dephosphorylation. To evaluate whether Trn and Ptp52F are part of the same pathway in vivo, we examined motor axon guidance in mutant embryos. trn and Ptp52F mutations produce identical phenotypes affecting the SNa motor nerve. The genes also display dosage-dependent interactions, suggesting that Ptp52F regulates Trn signaling in SNa motor neurons.

* Corresponding author. Mailing address: Division of Biology, Caltech, 114-96, 1200 E. Pasadena Blvd., Pasadena, CA 91125. Phone: (626) 395-8352. Fax: (626) 568-0631. E-mail: zinnk{at}caltech.edu

{triangledown} Published ahead of print on 30 March 2009.

{dagger} Supplemental material for this article may be found at http://mcb.asm.org/.

{ddagger} Present address: Joint Science Department, W. M. Keck Science Center, 25 N. Mills Ave., Claremont, CA 91711.

Molecular and Cellular Biology, June 2009, p. 3390-3400, Vol. 29, No. 12
0270-7306/09/$08.00+0     doi:10.1128/MCB.01764-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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