LIM Domain Binding Research Articles

Isolation and cloning of a novel cDNALDB1 encoding human LIM domain binding protein

Primers for screening cDNA library have been designed according to EST AA453734 which is corresponding to the mouse LIM domain binding protein Ldbl. Arrayed human fetal brain cDNA library has been screened by PCR and routine hybridization method. A 2398 bp-cD-NA clone has been obtained. The cDNA encodes a 347 amino acids protein highly homologous to the mouse Ldbl,Xenopus Xldbl andDrosophila Chip. It also contains an LIM binding domain and a nuclear localization signal. It has been namedLDB1 ( LIM domain binding protein 1), GenBank accession number is AF052389. Northern blot showed a 2.4 kb band, and the expression amounts ofLDBI in heart, brain and lung were considerably higher than those in other tissues.

Characterization of Lhx9, a novel LIM/homeobox gene expressed by the pioneer neurons in the mouse cerebral cortex

In order to explain the phenotype observed in Lhx2 mutant embryos, we previously proposed that an Lhx2 related gene might exist. We now have cloned a new LIM/homeobox gene called Lhx9. Lhx9 is closely related to Lhx2 and is expressed in the developing central nervous system (CNS). Lhx9 and Lhx2 have expression patterns that overlap in some areas but are distinct in others. Thus, in some developmental domains these two highly related proteins may be functionally redundant. Lhx9 is expressed in the pioneer neurons of the cerebral cortex, while Lhx2 is expressed throughout the cortical layers. Postnatally, Lhx9 is expressed in the inner nuclei of the cerebellum, while Lhx2 is in the granular layer. In the developing limbs, both genes are highly expressed in a similar pattern. Based on the expression pattern and the developmental regulation of Lhx9, we propose that Lhx9 may be involved in the specification or function of the pioneer neurons of the cerebral cortex. We show that both Lhx9 and Lhx2 bind the LIM domain binding protein Ldb1/Nli1/Clim2.

Genomic structure, alternative transcripts and chromosome location of the human LIM domain binding protein 1 gene LDB1

By protein interaction screening using a radioactive LMO2 protein probe we have isolated a LIM domain binding protein. The gene shows high homology to independently isolated genes from mouse, Xenopus and Drosophila called Ldb1/Nli/Clim-2, Xldb1 and Chip, respectively. The human and mouse genes differ by only two amino acids, suggesting that the gene that we have isolated is the human homologue. Here we describe the genomic organization, alternative transcript forms and the chromosome mapping of the human gene LDB1 (alias NLI). The gene is spread over at least 12 kb and has 11 exons. Preceding the described ATG initiation site in the mouse a highly conserved region between mouse, chicken and human was detected with a second possible in frame initiation site coding for further 36 amino acids. An alternative splice site adding six nucleotides corresponding to the addition of two amino acids at the end of exon 10 was found. The gene was mapped to chromosome 10q24→q25 by in situ hybridization, a region frequently deleted in many types of cancer. Fine mapping with a radiation hybrid panel localized the gene in the interval between the markers D10S603 and D10S540.

Cloning and chromosomal localization of two novel human genes encoding LIM-domain binding factors CLIM1 and CLIM2/LDB1/NLI.

Cloning and chromosomal localization of two novel human genes encoding LIM-domain binding factors CLIM1 and CLIM2/LDB1/NLI.

Expression of LIM-domain binding protein (ldb) genes during zebrafish embryogenesis

LIM homeodomain proteins are developmental regulators whose functions depend on synergism with LIM domain binding proteins (Ldb proteins). We have isolated four members of the ldb gene family from the zebrafish, Danio rerio. Ldb1, Ldb2 and Ldb3 share 95%, 73% and 62% amino acid identity with mouse Ldb1, respectively. In overlay assays, Ldb proteins bind LIM homeodomain proteins and LMO1, but not zyxin or MLP. Whole mount in situ hybridization showed that zebrafish ldb1 is expressed ubiquitously from gastrulation onward. Ldb2 is ubiquitous at gastrulation, and later is found in many but not all tissues, especially the anterior central nervous system (CNS) and vasculature. Ldb3 mRNA was expressed primarily in the anterior CNS.

The LIM-domain binding protein Ldb1 and its partner LMO2 act as negative regulators of erythroid differentiation.

The nuclear LIM domain protein LMO2, a T cell oncoprotein, is essential for embryonic erythropoiesis. LIM-only proteins are presumed to act primarily through protein-protein interactions. We, and others, have identified a widely expressed protein, Ldb1, whose C-terminal 76-residues are sufficient to mediate interaction with LMO2. In murine erythroleukemia cells, the endogenous Lbd1 and LMO2 proteins exist in a stable complex, whose binding affinity appears greater than that between LMO2 and the bHLH transcription factor SCL. However, Ldb1, LMO2, and SCL/E12 can assemble as a multiprotein complex on a consensus SCL binding site. Like LMO2, the Ldb1 gene is expressed in fetal liver and erythroid cell lines. Forced expression of Ldb1 in G1ER proerythroblast cells inhibited cellular maturation, a finding compatible with the decrease in Ldb1 gene expression that normally occurs during erythroid differentiation. Overexpression of the LMO2 gene also inhibited erythroid differentiation. Our studies demonstrate a function for Ldb1 in hemopoietic cells and suggest that one role of the Ldb1/LMO2 complex is to maintain erythroid precursors in an immature state.