Liprins, a family of LAR transmembrane protein-tyrosine phosphatase-interacting proteins.

LAR family transmembrane protein-tyrosine phosphatases function in axon guidance and mammary gland development. In cultured cells, LAR binds to the intracellular, coiled coil LAR-interacting protein at discrete ends of focal adhesions, implicating these proteins in the regulation of cell-matrix interactions. We describe seven LAR-interacting protein-like genes in humans and Caenorhabditis elegans that form the liprin gene family. Based on sequence similarities and binding characteristics, liprins are subdivided into alpha-type and beta-type liprins. The C-terminal, non-coiled coil regions of alpha-liprins bind to the membrane-distal phosphatase domains of LAR family members, as well as to the C-terminal, non-coiled coil region of beta-liprins. Both alpha- and beta-liprins homodimerize via their N-terminal, coiled coil regions. Liprins are thus multivalent proteins that potentially form complex structures. Some liprins have broad mRNA tissue distributions, whereas others are predominately expressed in the brain. Co-expression studies indicate that liprin-alpha2 alters LAR cellular localization and induces LAR clustering. We propose that liprins function to localize LAR family tyrosine phosphatases at specific sites on the plasma membrane, possibly regulating their interaction with the extracellular environment and their association with substrates.

The highly organized and coordinated response of cells to diverse extracellular stimuli is partially mediated by tyrosine phosphorylation of proteins, some of which relay information from the cell surface to the nucleus and others of which control cytoskeletal organization. The degree of tyrosine phosphorylation of such signaling proteins, including enzymes, adapter proteins, and structural proteins, is regulated by the concerted activities of protein-tyrosine kinases and protein-tyrosine phosphatases (PTPases). 1 Both protein-tyrosine kinases and PTPases comprise large gene families encoding transmembranetype and intracellular-type enzymes (1,2). The physiological role of many protein-tyrosine kinases, and some PTPases, is well documented (3)(4)(5)(6). Recent genetic analysis of LAR-like transmembrane PTPases indicates that members of this subfamily play a role in Drosophila axon guidance (7,8) and murine mammary gland development and function (9). About half of the embryos with Drosophila LAR (DLAR)-inactivating mutations die as late instar larvae, and the other half die before or at eclosion (7). Examination of the nervous systems of DlarϪ/Ϫ mutant embryos revealed specific defects in motor axon guidance and, to a lesser degree, in the formation of certain CNS axon pathways. Female mice with a targeted disruption of the Lar gene are incapable of delivering milk due to impaired terminal differentiation of alveoli at late pregnancy (9). Consequently, the glands fail to switch to a lactational state and rapidly involute postpartum. The molecular basis for the axon guidance defect in the DlarϪ/Ϫ mutants and the impaired development of mammary alveoli in the LarϪ/Ϫ mutant mice is unknown, but given that axon guidance, as well as mammary epithelial differentiation and lactation, is regulated by soluble factors, cell-cell interactions, and cell-matrix interactions, it is likely that DLAR and LAR function in one or more of these signaling pathways (10,11).
LAR and DLAR are members of the LAR subfamily of transmembrane PTPases, which consists of the highly related vertebrate LAR (12,13), PTP␦ (14 -16), and PTP (17)(18)(19)(20), and Drosophila DLAR (21,22). These PTPases contain extracellular regions comprised of three N-terminal Ig-like domains and a variable number of fibronectin type III-like domains connected via a transmembrane segment to an intracellular region containing two PTPase domains. The overall architecture of the LAR family extracellular regions is similar to several cell or matrix adhesion molecules, indicating that these PTPases function as receptors for cell surface molecules and/or extracellular matrix molecules (3,23). Furthermore, human LAR localizes to focal adhesions (FAs) (24), which are sites of cellextracellular matrix interactions, and to sites of cell-cell contact (25,26). Because FAs are assembled by a tyrosine phosphorylation-dependent process following integrin ligation (27), LAR may play a role in FA disassembly.
Two proteins were identified that bind the LAR membranedistal D2 PTPase domain. One of these, Trio, contains a rac1 guanine nucleotide exchange factor domain, a rhoA guanine nucleotide exchange factor domain, a protein kinase domain, and several auxiliary domains (28). Because rac and rho are regulators of actin reorganization and cell growth (29), a LAR/ Trio complex may integrate multiple signals and determine the response of cells to diverse extracellular stimuli. The second protein, LAR-interacting protein 1 (LIP.1), is a coiled coil protein that colocalizes with LAR at FAs (24). LIP.1 may form rod-like dimers or higher order structures similar to other proteins that contain coiled coil ␣-helical domains, such as the myosin II heavy chain and intermediate filaments (30). The A, deduced amino acid sequence of human liprin-␤1, human liprin-␤2, and C. elegans celiprin-␤. B, deduced amino acid sequence of human liprin-␣2, human liprin-␣3, human liprin-␣4, and C. elegans celiprin-␣. Sequences are aligned with the liprin-␣1(LIP.1) sequence; residues conserved in three out of the four sequences are shown with a black background. Numbers followed by a prime symbol (Ј) indicate provisional amino acid numbering because the structures are incomplete. Underlined sequences are the LH domain sequences. C, the overall structures of ␣and ␤-liprins, with their N-terminal, coiled coil regions and their C-terminal LH domains are schematically depicted APC colorectal tumor suppressor gene product also contains coiled coil domains, and APC is believed to mediate the attachment of cadherin/catenin complexes to the cytoskeleton (31). LIP.1 does not appear to be tyrosine-phosphorylated and hence is unlikely to be a PTPase substrate (24). Instead, LIP.1 likely anchors LAR at FAs where LAR may dephosphorylate FAassociated protein(s) to alter FA assembly and/or signaling. Thus, the LAR/LIP.1 complex may represent a matrix/cytoskeletal linkage that augments the actin/integrin and cadherin/ catenin linkages by its intrinsic PTPase activity.
Herein we describe the identification and characterization of human and Caenorhabditis elegans LIP.1-related genes, which we have designated the liprin (derived from "LIP-related protein") gene family. Based on sequence homology and binding properties, liprins are divided into ␣-liprins and ␤-liprins. ␣-Liprins, including LIP.1 (renamed liprin-␣1) bind to the membrane-distal D2 PTPase domains of the LAR family PTPases, LAR, PTP␦, and PTP, whereas ␤-liprins bind to ␣-liprins but not to LAR family PTPases. Furthermore, both ␣and ␤-liprins homodimerize via their N-terminal, coiled coil regions. Whereas some of the liprins have a broad mRNA tissue distribution, others are highly restricted, particularly to brain. Co-expression studies indicate that liprin-␣2 alters the cellular distribution of LAR, supporting a role for liprins in localizing LAR family members to specific sites within the cell and creating specific linkages between the extracellular environment and the cytoskeleton.
C. elegans Expression Analysis-Animals were injected with plasmid pPD.celiprin-␣-GFP and pPD.celiprin-␤-GFP DNAs at 50 ng/l using lin-15 as a marker (35,36). At least two independent extrachromosomal array lines were examined for each construct. GFP was observed in both the cytoplasm and nucleus for both constructs, despite the SV40 nuclear localization signal in the GFP vector. Adobe Photoshop was used to create "negatives" of black and white images originally captured using a Sensys camera and ImagePro Plus software.
Cell Transfections-COS-7 cell transient transfections were done by the DEAE-dextran/Me 2 SO method using 2 g of plasmid DNA per 2 ϫ 10 5 cells per 9-cm 2 dish, and cells were harvested ϳ20 h after transfection (33). Proteins were metabolically labeled with [ 35 S]methionine during the final 4 h prior to harvesting of cells.
Immunofluorescence-COS-7 cells were plated on glass coverslips 5 h following transfection with pMT.2-based expression plasmids and grown for ϳ20 h prior to staining. Cells were rinsed in PBS, fixed in 2% paraformaldehyde/PBS for 15 min, and then permeabilized for 10 min in 0.1% Triton X-100/PBS-containing 2% horse serum. Nonspecific antibody binding sites were blocked by a 30-min incubation in blocking buffer (10% normal goat serum in PBS). To detect liprin-␣1 and liprin-␤1, permeabilized cells were exposed to the anti-liprin-␣1 mAb anti-LIP.1.77 mAb and the anti-liprin-␤1.68.1 mAb at a concentration of 2 g of ␣-LIP.1.77/ml blocking buffer and a 1:3 dilution of anti-liprin-␤1.68.1 hybridoma supernatant in blocking buffer for 1 h and washed, and the primary antibody was detected with a 30-min treatment of 1:1000 goat anti-mouse IgG2a-Texas red (Southern Biotechnology, Birmingham, AL) and 1:1000 goat anti-mouse IgG1-fluorescein isothiocyanate (Southern Biotechnology). To detect LAR and HA-tagged liprin-␣2, permeabilized COS cells were exposed to a 1:1:1 mixture of the anti-LAR mAbs, 75.3A, 11.1A, and 128.4A at 2 g/ml blocking buffer, and/or the anti-HA mAb 12CA5 at 0.5 g/ml blocking buffer for 1 h and washed, and the primary antibody detected as above with a 30-min treatment of 1:1000 goat anti-mouse IgG2b-Texas red and 1:1000 goat anti-mouse IgG1-fluorescein isothiocyanate. Slides were mounted in a polyvinyl alcohol medium and viewed on a Olympus BX60 microscope equipped for epifluorescence. Photographs were taken on Kodax Ektachrome film.

LIP.1 Is the Prototype Member of the Evolutionarily Conserved Liprin
Family-LIP.1 is a coiled coil protein originally isolated by virtue of its binding to the intracellular region of the LAR transmembrane PTPase and was shown to co-localize with LAR at FAs (24). To learn more about LIP.1 function, we performed an interaction trap screen to identify additional LIP.1-binding proteins (32). Using as bait the non-coiled coil, C-terminal region of LIP.1 (aa 794 -1202), we isolated two novel proteins we have named liprin-␤1 (aa 678 -1005; Fig. 1A) and liprin-␤2 (aa 257Ј-783Ј; Fig. 1A), in addition to the expected LAR and PTP. Sequence determination of liprin-␤1 cDNA clones predict that liprin-␤1 is a 1005-amino acid long protein, the primary sequence of which is similar to LIP.1 (25% sequence identity; Fig. 1A). Liprin-␤1 was named LIP.1-related protein; ␤1 indicates that liprin-␤1 is the first member of the ␤ subfamily of liprins (see below). Consequently, LIP.1 was renamed liprin-␣1, because it is the first member of the liprin-␣ subfamily.
A notable feature of liprins is the high degree of sequence conservation within a ϳ250-amino acid domain located within the C-terminal, non-coiled coil region (underlined sequences in Fig. 1, A and B). Within this domain, which we designate the liprin homology (LH) domain, 34 amino acids are absolutely conserved in all six human liprins and the two C. elegans liprins, and 95 amino acids are conserved in at least six out of the eight members. The extensive sequence conservation of LH domains suggests that these domains are functionally important. One possibility is that LH domains are protein-protein interaction domains, because the LH domain in liprin-␣1 binds to LAR (24) and to liprin-␤1 (see below, and data not shown). Thus, LH domains may be novel protein-protein interaction domains. The overall structures of ␣and ␤-liprins, with their N-terminal, coiled coil regions and their C-terminal LH domains are schematically depicted for liprin-␣1 and liprin-␤1 in Fig. 1C.
The relatively high degree of sequence conservation between the mammalian ␣-liprins and C. elegans celiprin-␣ (50 -58% identity), as well as the high degree of conservation between the mammalian ␤-liprins and C. elegans liprin-␤ (29 -31% identity), indicates that liprins are evolutionarily conserved. Based on the predicted phylogenetic tree (Fig. 1D), it is likely that ␣and ␤-liprins were derived from an ancestral gene by gene duplication prior to the divergence of chordates and nematodes.
Tissue-specific Expression of Human Liprins-The human LAR, PTP␦, and PTP PTPases have distinct, but overlapping, mRNA tissue distributions (20). For instance, all three mRNAs are expressed in brain, whereas only LAR and PTP mRNA are expressed in kidney and pancreas. To determine the tissue distribution of ␣and ␤-liprin mRNAs, Northern blot analysis was performed using poly(A)ϩ RNA isolated from various human tissues and gene-specific cDNA probes (Fig. 2). The 5.3-kb liprin-␣1 mRNA and the less abundant 6.8-and 4.0-kb liprin-␣1 mRNAs are expressed in all eight samples (heart, lung, placenta, lung, liver, skeletal muscle, kidney, and pancreas), whereas the 6.5-kb liprin-␣2 mRNA and the 5.0-kb liprin-␣3 mRNA are present only in the brain sample. The 7.5-kb liprin-␣4 mRNA is present only in the heart, brain, and skeletal muscle samples. Both the 7.0-kb liprin-␤1 and the 3.9-kb liprin-␤2 are broadly expressed, being present either in all eight samples (liprin-␤2) or in seven of the eight samples (liprin-␤1 is absent in the liver sample). In addition to the 3.9-kb liprin-␤2 mRNA species, there is also a 5.1-kb species present in the heart and skeletal muscle samples. These results indicate that liprin mRNAs, like LAR family PTPase mRNAs, have distinct, but overlapping, expression patterns. The tissue restriction of liprin-␣2 and liprin-␣3 mRNA to brain suggests that these liprins may play specific roles in brain, perhaps in localizing PTP␦ and PTP, which are both predominately expressed in the brain.
Expression of C. elegans Liprins-The expression of the C. elegans liprins celiprin-␣ and celiprin-␤ was examined using celiprin promoter driven expression of the GFP in transgenic nematodes (35). Two extrachromosomal array lines were characterized for each GFP reporter construct (Fig. 3). Celiprin-␣-GFP expression is detected in vulval muscle and other cells near the vulva; in neurons located in the lateral ganglion, posterior ganglion, ventral cord, and lateral body; and in pharyngeal and body wall muscle cells (Fig. 3, A and B). Celiprin-␤1-GFP expression is seen in pharyngeal muscle, particularly posterior bulb, adjacent to the dorsal and ventral cord (but not in ventral cord neurons), and in body wall muscles (Fig. 3, C  and D). Overall, celiprin-␣ and celiprin-␤ expression appears predominately in neurons and muscle cells, with celiprin-␣ and celiprin-␤ being co-expressed in pharyngeal and body wall muscle but not in any other obvious regions.  1, 4, and 7), liprin-␣2 (lanes 2, 5, and 8), or liprin-␤1 (lanes 3, 6, and 9). 16 h after transfection, cells were metabolically labeled with [ 35 S]methionine for 4 h. Following labeling, cell extracts were prepared, and immunoprecipitation analysis was performed using the anti-HA antibody 11A. Control precipitations using the anti-liprin-␣1 mAb, anti-LIP.1.77, an anti-liprin-␣2 mouse polyserum, or anti-liprin-␤1.68.1 hybridoma supernatant demonstrated that all three of the full-length liprins were about equally well expressed in all of the co-transfections (data not shown). Immunoprecipitated proteins were resolved by 10% SDS-PAGE and visualized by autoradiography after 16 h (lanes 1-6) or 40 h (lanes 7-9). Liprin-␤1 (lanes 3 and 6) was not observed even in the 40 h exposure (data not shown). Molecular mass standards in kDa are shown at the right of the figure.
Interaction between the C-terminal Regions of ␣-Liprins and ␤-Liprins-Liprin-␤1 and liprin-␤2 were identified in the interaction trap screen for liprin-␣1-binding proteins. Both the liprin-␣1 bait and the original liprin-␤1 and liprin-␤2 interactors isolated contain only the C-terminal, non-coiled coil regions, demonstrating that liprin-␣1/liprin-␤1 and liprin-␣1/liprin-␤2 binding occurs via the C-terminal, non-coiled coil regions. To determine whether the C-terminal regions of liprin-␣2 and -␣3 also bind ␤-liprins, interaction trap assays were performed. Both the C-terminal, non-coiled coil region of liprin-␣2 (aa 821-1257) and liprin-␣3 (aa 3Ј-443Ј) bound the C-terminal region of liprin-␤1 and -␤2, indicating that a general property of ␣-liprins is the ability to bind ␤-liprins through their Cterminal regions, which contain the LH domains (Table I). The binding of ␣and ␤-liprins was not observed in co-precipitation experiments using mammalian cells (data not shown). The reason for this lack of binding is unknown, but possibly the ␣and ␤-liprin interaction is sensitive to the detergents present in the lysis buffer. Interaction of liprins via their C-terminal regions was restricted to ␣/␤ interactions because the C-terminal regions of ␣-liprin subfamily members did not bind other ␣-liprins, and the C-terminal region of liprin-␤1 did not bind liprin-␤2 (Table I). Taken together, these data indicate that the C-terminal, non-coiled coil regions of ␣-liprins bind to the Cterminal regions of ␤-liprins.
To determine whether ␣and ␤-liprins interact in vivo, COS cells were co-transfected with liprin-␣1 and -␤1 expression vectors, and co-localization was assessed by immunofluorescence (Fig. 5). Liprin-␣1 (Fig. 5B, red) and liprin-␤1 (Fig. 5A,  green) co-localize predominantly to the plasma membrane of COS cells (Fig. 5C, double exposure of co-localized green and red results in yellow/orange). The localization of either lip-rin-␣1 or -␤1 in singly transfected COS cells is similar to their localization in co-transfected cells (data not shown), indicating that localization of liprin-␣1 or -␤1 to the membrane in COS cells is independent of the expression of the second liprin. The co-localization of liprin-␣1 and -␤1 in COS cells supports the possibility that ␣and ␤-liprins interact in vivo. The ability of liprins to dimerize via their N-terminal regions to form ␣/␣ and ␤/␤ dimers, as well as their ability to form ␣/␤ heterodimers via their C-terminal regions, suggests that liprins are multivalent proteins that form complex structures.
Liprin-␣2 Expression Affects LAR Cellular Localization-To determine whether liprin-␣2, like -␣1, colocalizes with LAR in cells, transiently transfected COS cells were analyzed by immunofluorescence (Fig. 7). COS cells were transfected with various combinations of expression vectors encoding LAR, a LAR truncation mutant (LAR-D1) that lacks the ␣-liprin interacting D2 PTPase domain, and HA-liprin-␣2. In cells transfected with LAR only, LAR (green) was uniformly distributed throughout the plasma membrane and Golgi (Fig. 7A), whereas in liprin-␣2-only transfected cells, liprin-␣2 (red) was observed in large plaque-like structures at the cell surface (Fig. 7B). In cells co-expressing LAR (green) and liprin-␣2 (red) both proteins co-localized at the cell surface in plaque-like structures and to a lesser extent at ruffling edges (single exposures of the same field for LAR (Fig. 7C) and liprin-␣2 (Fig. 7D). The specificity of the LAR-liprin-␣2 association is supported by the lack of significant co-localization of LAR-D1 with liprin-␣2 (Fig. 7, single exposures of the same field for LAR-D1 (Fig. 7E) and liprin-␣2 (Fig. 7F)). In contrast to the punctate expression pattern of LAR in the LAR/liprin-␣2 co-expressing cells (Fig.   7C), the LAR-D1 expression pattern in the LAR-D1/liprin-␣2 co-expressing cells (Fig. 7E) is similar to the expression pattern of LAR in the LAR-only transfected cells (Fig. 7A). Furthermore, the liprin-␣2 expression pattern is similar in the liprin-␣2-only transfected cells and in the LAR/liprin-␣2 or LAR-D1/ liprin-␣2 doubly transfected cells (Fig. 7, B, D, and F), indicating that LAR expression does not alter liprin-␣2 localization. Taken together, these results demonstrate that LAR and liprin-␣2 co-localize in COS cells, and that the LAR membrane-distal D2 PTPase domain is required for co-localization and LAR clustering. Thus, liprin expression modifies LAR distribution. DISCUSSION We describe the liprins, a novel gene family that contains at least six mammalian and two C. elegans members. The overall predicted structure of ␣-liprins and ␤-liprins is an N-terminal, coiled coil region and a C-terminal, non-coiled coil region. This structure suggests that the liprin N-terminal regions intertwine to form rod-like structures, similar to those seen in intermediate filaments and myosin II heavy chains (30). The prototype member of this family, LIP.1 (renamed liprin-␣1), was previously identified as a LAR PTPase-binding protein and is thought to function in anchoring LAR at FAs (24). Based on   (16)), PTP (aa 1189 -1452 (46)), and CD45 (aa 584 -1281 (47)) fused to the LexA DNA binding domain (the baits) or liprins (see Fig. 1 sequence homology, as well as their binding to LAR family PTPases or to themselves, liprins are subdivided into ␣-liprins and ␤-liprins. The characterization of the liprins genes suggests several general properties of liprins: 1) the N-terminal, coiled coil region of ␣-liprins mediates homodimerization, as well as heterodimerization with other ␣-liprin subfamily members. The coiled coil region of ␤-liprins also allows for homodimerization and possibly for heterodimerization with other ␤-liprins. The coiled coil regions of ␣and ␤-liprins do not heterodimerize. 2) ␣-Liprins and ␤-liprins interact via their C-terminal LH domains. However, ␣-LH domains do not bind other ␣-LH domains, and ␤-LH domains do not bind other ␤-LH domains. 3) Only ␣-LH domains, not ␤-LH domains, bind to the membranedistal D2 domain of LAR family PTPases.
The ability of the N-terminal, coiled coil regions to form ␣/␣ or ␤/␤ dimers and the C-terminal LH domains to form ␣/␤ dimers suggests that liprins are multivalent proteins that form complex structures. Such structures could function as scaffolds for the recruitment and anchoring of LAR family PTPases. For instance, in tissues such as brain, in which all the known ␣and ␤-liprins are expressed, as well as LAR, PTP␦, and PTP, the potential complexities of the interaction between liprins and PTPases are substantial. Distinct combinations of ␣and ␤-liprins may determine where in the plasma membrane particular PTPases are located and determine the protein composition of the liprin/PTPase complexes. It is unknown whether ␣-liprins can simultaneously bind LAR family PTPases and ␤-liprins or whether the PTPases and ␤-liprins compete for ␣-liprin binding. LAR family PTPases bound to ␣-liprins may also be brought together with other liprin-binding proteins by liprin dimerization.
C. elegans liprins may function in a manner similar to mammalian liprins in LAR family PTPase signaling. Indeed, there exists a LAR-like gene in C. elegans (CECO9D8 -1/2; Gen-Bank TM accession number Z46811) that is predicted to contain an extracellular region composed of Ig-like and fibronectin III-like domains, connected via a transmembrane peptide to an intracellular region with two PTPase domains. However, because the expression pattern of celiprin-␣ and -␤ is only partially overlapping, it is unclear whether celiprin-␣ and -␤ interaction is essential for liprin function in C. elegans. If liprin function, at least in part, depends on the interaction of ␣and ␤-liprins, then one would assume that there are additional C. elegans liprins or proteins that functionally substitute for liprins. Alternatively, the function of C. elegans liprins does not require ␣/␤ association.
Based on the binding properties of liprins, we postulate that liprins recruit LAR family PTPases to specific areas within the plasma membrane, as well as facilitating the recruitment/anchoring of other signaling proteins. A role for ␣-liprins in localizing LAR family PTPases within the cell was initially indicated by the co-localization of LAR and liprin-␣1 to discrete ends of FAs (24). Such a role for other liprins is supported by the altered cellular distribution of LAR in LAR/liprin-␣2 coexpressing COS cells. In singly transfected cells, LAR is expressed homogeneously throughout the plasma membrane, whereas liprin-␣2 is distributed into large plaque-like structures and to the cell edges. In doubly transfected cells, LAR is redistributed to the liprin-␣2 aggregates, indicating that lip-FIG. 7. Liprin-␣2 expression alters LAR cellular distribution. Immunofluorescence images of cells transiently transfected with expression vectors encoding LAR and stained for LAR (green) (A); encoding liprin-␣2 and stained for liprin-␣2 (red) (B); encoding LAR and liprin-␣2 and stained for LAR and liprin-␣2, photographed for LAR (green) (C) and photographed for liprin-␣2 (red) (D); encoding LAR-D1 and liprin-␣2 and stained for LAR and liprin-␣2, photographed for LAR (green) (E) and photographed for liprin-␣2 (red) (F). Examples of LAR and liprin-␣2 co-localization are indicated by arrows. COS-7 cells were plated onto coverslips 5 h after being transiently transfected with the pMT.HA-Liprin-␣2 (aa 3-1257, HA-tagged), pMT.LAR (aa 1-1881), and pMT.LAR-D1 (aa 1-1615, which lacks the ␣-liprin binding PTPase D2 domain) expression vectors. 16 h following plating onto coverslips, cells were fixed, permeabilized, and stained individually or simultaneously with the anti-LAR mAb 11.1A/75.3A/128.4A mixture and/or the anti-HA 12CA5 mAb, followed by isotype-specific, goat anti-mouse fluorescein isothiocyanate or Texas red-conjugated Abs as described under "Experimental Procedures." Scale bar represents 25 m. rin-␣2 recruits and clusters LAR. Controlling LAR family PTPase localization is likely to be a key feature in determining the substrates that these PTPases dephosphorylate because there is currently little evidence to support regulated catalytic activity for LAR family PTPases. Further insight into the physiological function of liprins and LAR family PTPases should be greatly aided by genetic analyses of the C. elegans liprins and LAR-like PTPase(s).