Identification and characterization of LMO 4 , an LMO gene with a novel pattern of expression during embryogenesis

Abstract

LMO4 is a novel member of the LIM-only (LMO) subfamily of LIM domain-containing transcription factors. LMO1, LMO2, and LMO4 have distinct expression patterns in adult tissue, and we demonstrate that nuclear retention of LMO proteins is enhanced by the nuclear LIM interactor (NLI). In situ hybridization to early mouse embryos of 8-14.5 days revealed a complex pattern of LMO4 expression spatially overlapping with NLI and LHX genes. LMO4 expression in somite is repressed in mice mutant for the segment polarity gene Mesp2 and expanded in Splotch mutants. During jaw and limb outgrowth, LMO4 and LMO2 expression define mesenchyme that is uncommitted to regional fates. Although both LMO2 and LMO4 are activated in thymic blast cells, only LMO4 is expressed in mature T cells. Mesenchymal and thymic blast cell expression patterns of LMO4 and LMO2 are consistent with the suggestion that LMO genes inhibit differentiation.The LIM domain, an approximately 55-residue, cysteine-rich zinc-binding motif, is present in a variety of proteins including LIM homeobox (LHX) proteins that contain two LIM domains and one homeodomain. LHX genes are expressed in many types of neurons and other cell types, and deletion of LHX genes results in the loss of cell fate (1). Mice mutant for LHX1 have diminished organizer activity that results in lack of head structures anterior to rhombomere 3 (2). In the central nervous system, development of forebrain and pituitary derivatives are defective in mice mutant for LHX2, LHX3, or LHX4 (1), while activation of the LHX gene Isl1 is essential for the survival of motor neurons and neighboring interneurons (3).LMO2 represents a family of nuclear LIM-only (LMO) proteins that lack a DNA-binding homeodomain (4, 5). Unregulated LMO2 expression induces T cell tumors (6), while deletion blocks hematopoietic development (7,8). The mechanism of LMO2 activity is thought to be the LIM domaindependent assembly of transcription complexes and transcription regulation (9).LIM domains of nuclear proteins bind with high affinity to the widely expressed nuclear LIM interactor (NLI) and with lesser affinity to other transcription factors (10-12). Dimeric NLI supports assembly of heteromeric complexes of LIM proteins (13), and CHIP, the Drosophila ortholog of NLI, mediates enhancer-promoter interactions of the cut and ultrabithorax genes, presumably by complex formation with transcription factors (14).To identify novel LIM domain transcription factors, we screened two mouse embryonic expression libraries by using the LIM interaction domain (LID) of NLI. We report the isolation and characterization of LMO4, a novel LIM-only gene, which is highly expressed in the T lymphocyte lineage, cranial neural crest cells, somite, dorsal limb bud mesenchyme, motor neurons, and Schwann cell progenitors. Somitic expression of LMO4 is repressed in mice mutant for the segment polarity gene Mesp2. LMO4 and LMO2 expression in the jaw, limb, and thymus defines cells that are uncommitted to cell fates. Interaction with NLI mediates the n...

Dynamic spatiotemporal expression of LIM genes and cofactors in the embryonic and postnatal cerebral cortex

“…Of the set of 17 LIM genes comprising Lhx1-9, Lmx1a, 1b, Isl1, 2, and Lmo1-4, we focused on only those genes for which our preliminary studies or published reports from other groups showed expression in the dorsal telencephalon (Boehm et al, 1991;Foroni et al, 1992;Fujii et al, 1994;Porter et al, 1997;Sheng et al, 1997;Kenny et al, 1998;Bertuzzi et al, 1999;Retaux et al, 1999;Millonig et al, 2000). Lhx3,4,6,7,8,Lmx1b, and Isl1, 2 were excluded because previously reported expression patterns reveal their expression to be in only ventral but not dorsal telencephalon, or restricted to nontelencephalic CNS regions, in addition to non-CNS structures (Thor et al, 1991;Li et al, 1994;Tsuchida et al, 1994;Zhadanov et al, 1995;Yamashita et al, 1997;Chen et al, 1998;Grigoriou et al, 1998;Kitanaka et al, 1998).…”

The LIM-only protein, LMO4, and the LIM domain-binding protein, LDB1, expression in squamous cell carcinomas of the oral cavity

“…LMO4 and LDB1 are ubiquitously expressed in the mouse embryos, including epithelial and mesenchymal areas, when compared to the exclusive expression of other LMO family members and LDB2 in neuronal and haematopoietic cells (Visvader et al, 1997;Kenny et al, 1998;Sugihara et al, 1998;Toyama et al, 1998;Hermanson et al, 1999;Thaler et al, 2002). The LIM domain of LDBs contributes to the binding of transcription factors, including LIM-homeodomain, zinc-finger and basic helixloop -helix (bHLH) proteins (Agulnick et al, 1996;Jurata et al, 1996;Bach et al, 1997;Morcillo et al, 1997).…”

“…The most recently identified member, LMO4, shares only 50% homology with the LIM domains of other LMO proteins. The LMO4 gene is widely distributed in embryonic tissues (Kenny et al, 1998;Sugihara et al, 1998), and involved in negative regulation of breast carcinoma cell differentiation (Visvader et al, 2001). LMO4 binds with a high affinity to the LIM domain-binding proteins, LDB1 (CLIM2, NLI1) and LDB2 (CLIM1) (Agulnick et al, 1996;Jurata et al, 1996;Sugihara et al, 1998).…”

“…LDB proteins bind to transcription factors directly or indirectly mediated through LMO proteins, and then bridge a unique bipartite DNA sequence separated by about one helix turn from each other (Agulnick et al, 1996;Jurata et al, 1996;Wadman et al, 1997;Rabbitts, 1998). Both LMOs and LDBs are widely expressed during development (Kenny et al, 1998;Millan et al, 1998;Toyama et al, 1998;Hermanson et al, 1999) and appear to have essential functions in cell proliferation and lineage determination, and oncogenesis Milán et al, 1998;Rabbitts, 1998;Thaler et al, 2002).…”

Identification of the LMO4 gene encoding an interaction partner of the LIM-binding protein LDB1/NLI1: a candidate for displacement by LMO proteins in T cell acute leukaemia

“…Examination of the protein sequence revealed that this cDNA clone corresponded to a mRNA encoding a new member of the LIM-only LMO family of proteins. A similar cDNA has recently been described (Kenny et al, 1998) and the sequence of the human counterpart (which is identical in translated product with the mouse sequence reported here) was previously deposited in the Genbank database by J Racevskis, A Dill and H Ruan (Accession number: U24576). In keeping with other members of the LMO family, this new member is designated Lmo4.…”