FEBS Letters 355 (1994) 223 228 FEBS 14801 Developmental regulation of gene expression for the MPTPg isoforms in the central nervous system and the immune system Kazuya Mizuno, Kiminori Hasegawa, Mami Ogimoto, Tatsuo Katagiri, Hidetaka Yakura* Tokyo Metropolitan Institutefor Neuroscience, Fuchu, Tokyo 183, Japan Received 21 September 1994; revised version received 20 October 1994 Abstract MPTP6 is a murine transmembrane protein tyrosine phosphatase which has three isoforms, types A-C, differing in the structure of the extracellular regions. In this study, we examined MPTP~ isoform expression in the brain and the immune system at discrete developmental or differentiation stages. RT-PCR analysis demonstrated that another isoform, type D, is transcribed from the MPTP~ gene. In\the brain, only type D was expressed until postnatal day 7 (P7), but after P14, all four isoforms were detected. In contrast, the spleen, thymus and all the hematopoietic cell lines examined express only types B and C isoforms. An in situ hybridization study showed that MPTP6 mRNA is diffusely expressed throughout the spleen, but its expression in the thymus is restricted to the medullary region. Key words: Protein tyrosine phosphatase; Cell differentiation; Isoform 1. Introduction Protein tyrosine phosphorylation plays a central role in the regulation of normal cell activation, proliferation and differen- tiation [1-3]. The phosphorylation state of tyrosine residues on cellular proteins is strictly controlled by protein tyrosine ki- nases (PTKs) and protein tyrosine phosphatases (PTPs) under physiological conditions. While a number of PTKs, identified as growth factor receptors and oncogene products, are well characterized, the understanding of structure and function of PTPs has been very limited. In 1988, it was demonstrated that the cytoplasmic region of CD45, a transmembrane molecule on the hematopoietic cells, has a sequence similar to a cytoplasmic PTP (PTP1B) [4] and has intrinsic PTP activity [5]. Since then, more than 40 PTPs have been cloned from various species and tissues using either cross-hybridization or a polymerase chain reaction (PCR) technique based on the sequence similarity of the consensus sequences in the PTP domains [6,7]. They are classified into two groups: soluble-form PTPs with a single PTP domain, and transmembrane PTPs (also referred to as recep- tor-type PTPs; RPTPs), almost all of which contain two PTP domains in the cytoplasmic regions. Based on the structural diversity of the extracellular region, RPTPs have been subdivided into four groups by Fischer et al. [8]. Among them, type II RPTPs are characterized by the pres- ence of varying numbers of immunoglobulin (Ig)-like and fi- bronectin type III repeat (FN-III)-like domains in the extracel- lular regions and include LAR [9,10], PTP6 [11,12], PTPx [13], PTP/t [14], PTPa (NE-3) [15,16] and Drosophila DPTP [10]. Since these structural motifs are also utilized by cell adhesion molecules such as the neural cell adhesion molecule (N-CAM), it has been postulated that type II RPTPs might be involved in cell adhesion. Indeed, PTPlc and PTP/2 were shown to mediate homophilic cell adhesion when expressed in insect cells using recombinant baculovirus expression systems [17-19]. However, *Corresponding author. Fax: (81) (423) 21-8678. Abbreviations. PTP, protein tyrosine phosphatase; PTK, protein tyro- sine kinase; Ig, immunoglobulin; FN-III, fibronectin type III repeat; RT-PCR, reverse transcription-polymerase chain reaction; GAPDH, glyceraldehyde 3-phosphate dehydrogenase. physiological ligands of type II RPTPs and how the binding of ligands influences the PTP activity still remain to be clarified. It is well known that several PTKs, such as the src-family of PTKs, are abundantly expressed in the central nervous sys- temm [20-23] and the immune system (reviewed in [3]). The receptors for nerve growth factor and several neurotropic fac- tors have intrinsic PTK activity [24-27]. In the immune system, soluble-form PTKs have been shown to be associated with antigen receptors (reviewed in [3]) and growth factor receptors [28]. All these observations suggest that protein phosphoryla- tion is involved in the signal transduction for cell activation and proliferation. In addition, tyrosine phosphorylation was dem- onstrated to be modulated during the development of the cen- tral nervous system [29]. To analyze the mechanisms of regula- tion during differentiation from the perspective of PTPs, we have recently cloned and characterized a mouse type II RPTP, named MPTP~. The MPTP6 gene is expressed in the special- ized regions of the brain and in B cells, which shows a high degree of sequence similarity to LAR and PTPa, and generates at least three isoforms differing in the extracellular region pos- sibly by an alternative splicing mechanism [12]. Type A is com- posed of one Ig-like and four FN-III-like domains; the type B, one Ig-like and eight FN-III-like domains; and the type C, three Ig-like and eight FN-III-like domains [12] (Fig. 1). To elucidate the functional roles of MPTP~ in the central nervous system and the immune system, we tried to examine the expression of MPTP~ at discrete developmental or matura- tional stages by reverse transcription (RT)-PCR using isoform- specific primers, and to determine the localization of the MPTP6 gene expression within the lymphoid organs by in situ hybridization. The results herein demonstrated that the MPTP~ gene generates another isoform, the extracellular re- gion of which is composed of three Ig-like and four FN-III-like domains, that the spleen, thymus and all the hematopoietic cell lines tested express types B and C MPTP6 isoforms, and that in the brain, the expression of MPTP6 isoforms is developmen- tally regulated. Furthermore, MPTP6 mRNA is mainly ex- pressed in the medulla of the thymus and only sparsely in the cortex. All these results suggest that MPTP~ may be involved in the regulation of differentiation and maturation of the brain and lymphocytes. 0014-5793194l$7.00 © 1994 Federation of European Biochemical Societies. All rights reserved. SSDI 0014-5793(94)01 188-5