Characterization of the Lmo4 gene encoding a LIM-only protein: genomic organization and comparative chromosomal mapping

Dynamic expression and regulation by Fgf8 and Pou2 of the zebrafish LIM-only gene, lmo4

We report the expression of zebrafish lmo4 during the first 48 h of development. Like its murine ortholog, lmo4 is expressed in somitic mesoderm, branchial arches, otic vesicles, and limb (pectoral fin) buds. In addition, however, we report zebrafish lmo4 expression in the developing eye, cardiovascular tissue, and the neural plate and telencephalon. We demonstrate that expression in the rostral hindbrain requires acerebellar (ace/fgf8) and spiel ohne grenzen (spg/pou2) activity.

The protocadherin 11X/Y gene pair as a putative determinant of cerebral dominance in Homo sapiens

The cerebral torque, a bias from right frontal to left occipital across the anterior–posterior axis is arguably the defining feature of the human brain, and the foundation for language. What is its genetic basis? Handedness and anatomical data suggest that this torque is specific to humans relative to the extant great apes. Asymmetry deficits associated with sex chromosome aneuploidies implicate loci on both the X and Y chromosomes. A block from the Xq21.3 band was duplicated to the Y chromosome 6 million years ago (close to, and a possible cause of the chimpanzee/hominin separation) containing the human-specific gene pair PCDH11X/Y. PCDH11Y has been subject to positive selection through hominin evolution including 18 amino-acid changes to the longest isoform of the protein. The PCDH11X protein has been subject to five substitutions including two cysteines in the ectodomain. The gene pair can account for sex differences, for example, in cerebral asymmetry and language.

LIM only 4 is overexpressed in late stage pancreas cancer

Background

LIM-only 4 (LMO4), a member of the LIM-only (LMO) subfamily of LIM domain-containing transcription factors, was initially reported to have an oncogenic role in breast cancer. We hypothesized that LMO4 may be related to pancreatic carcinogenesis as it is in breast carcinogenesis. If so, this could result in a better understanding of tumorigenesis in pancreatic cancer.

Methods

We measured LMO4 mRNA levels in cultured cells, pancreatic bulk tissues and microdissected target cells (normal ductal cells; pancreatic intraepithelial neoplasia-1B [PanIN-1B] cells; PanIN-2 cells; invasive ductal carcinoma [IDC] cells; intraductal papillary-mucinous adenoma [IPMA] cells; IPM borderline [IPMB] cells; and invasive and non-invasive IPM carcinoma [IPMC]) by quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR).

Results

9 of 14 pancreatic cancer cell lines expressed higher levels of LMO4 mRNA than did the human pancreatic ductal epithelial cell line (HPDE). In bulk tissue samples, expression of LMO4 was higher in pancreatic carcinoma than in intraductal papillary-mucinous neoplasm (IPMN) or non-neoplastic pancreas (p < 0.0001 for both). We carried out microdissection-based analyses. IDC cells expressed significantly higher levels of LMO4 than did normal ductal epithelia or PanIN-1B cells (p < 0.001 for both) or PanIN-2 cells (p = 0.014). IPMC cells expressed significantly higher levels of LMO4 than did normal ductal epithelia (p < 0.001), IPMA (p < 0.001) and IPMB cells (p = 0.003).

Conclusion

Pancreatic carcinomas (both IDC and IPMC) expressed significantly higher levels of LMO4 mRNA than did normal ductal epithelia, PanIN-1B, PanIN-2, IPMA and IPMB. These results suggested that LMO4 is overexpressed at late stages in carcinogenesis of pancreatic cancer.

The LIM domain-only protein LMO4 is required for neural tube closure

Nuclear LIM domain-only proteins (LMOs), which consist of two closely spaced 50 amino acid Zn2+-finger protein interaction modules mediate interactions between several classes of transcription factors important for development. LMO2 is necessary for development of the entire hematopoietic system and overexpression of LMO1 or LMO2 results in human acute T cell leukemia. LMO4 is the most widely expressed LMO but its normal function is unknown. During development, LMO4 is expressed in dividing neuroepithelial cells within the ventricular zone along the entire rostrocaudal axis of the nervous system. In telencephalic and spinal cord regions of the CNS, LMO4 is highly expressed in ventral but is low in dorsal proliferating neuroepithelial cells. To understand the role of LMO4 during mouse development, we generated a homozygous null mutation in the gene. We found that LMO4 is required for proper closure of the anterior neural tube. In the absence of LMO4, elevation, bending, and proliferation of the ventral neural epithelium and consequent fusion of the prospective dorsal ends of the neural tube do not occur. LMO4 mutant mice die embryonically and exhibit exencephaly, which is associated with abnormal patterns of cell proliferation and with high levels of apoptotic cell death within the neuroepithelium. LMO4 is thus essential for normal patterns of proliferation and for survival of neural epithelial cells in the rostral neural tube. LMO4 is also expressed in Schwann cell progenitors after these contact neurites, a process mediated in part by neuregulin (Nrg).

Null mutation of the Lmo4 gene or a combined null mutation of the Lmo1/Lmo3 genes causes perinatal lethality, and Lmo4 controls neural tube development in mice

The LIM-only family of proteins comprises four members; two of these (LMO1 and LMO2) are involved in human T-cell leukemia via chromosomal translocations, and LMO2 is a master regulator of hematopoiesis. We have carried out gene targeting of the other members of the LIM-only family, viz., genes Lmo1, Lmo3 and Lmo4, to investigate their role in mouse development. None of these genes has an obligatory role in lymphopoiesis. In addition, while null mutations of Lmo1 or Lmo3 have no discernible phenotype, null mutation of Lmo4 alone causes perinatal lethality due to a severe neural tube defect which occurs in the form of anencephaly or exencephaly. Since the Lmo1 and Lmo3 gene sequences are highly related and have partly overlapping expression domains, we assessed the effect of compound Lmo1/Lmo3 null mutations. Although no anatomical defects were apparent in compound null pups, these animals also die within 24 h of birth, suggesting that a compensation between the related Lmo1 and 3 proteins can occur during embryogenesis to negate the individual loss of these genes. Our results complete the gene targeting of the LIM-only family in mice and suggest that all four members of this family are important in regulators of distinct developmental pathways.

Differential expression of LMO4 protein in Alzheimer's disease

The molecular bases of late-onset and sporadic Alzheimer's disease (AD) still have to be unraveled. Among putative candidates for molecular variations in AD, we propose LMO4 protein, a transcription regulator, involved in multiple protein complexes. We investigated changes in LMO4 immunoreactivity in vulnerable brain regions of AD cases and controls of comparable age. Immunocytochemical analysis revealed a high level of LMO4 expression in the entorhinal cortex (EC) and in the CA1 hippocampal region of the control brains and a consistent decrease in the AD brains, correlated with the amount of neurofibrillary tangles (NFT) degenerating neurones and the severity of senile plaques deposition. The decrease in LMO4 immunoreactivity resulted both from weaker immunoreactive signals and from a loss of immunoreactive neurones. LMO4 immunocytochemical staining appeared not to be colocalized with NFT in a majority of neurones. Its expression was weak in the dentate gyrus and stronger in CA3-4, two regions with no or low numbers of NFT, but there was no decrease in AD compared to control cases. In the frontal cortex, the ventro-infero-median region (area 12) showed a greater LMO4 expression than the polar one (area 9), but no decrease in AD was observed. As LMO4 has been proposed to inhibit cellular differentiation, it can be hypothesized that a reduced expression is associated in EC and CA1 with attempts of diseased neurones to differentiate (e.g. compensatory neuritogenesis). Taken together, these data indicate that LMO4 protein is involved in the complexity of the disease phenotype, at least as a secondary factor.

Defective neural tube closure and anteroposterior patterning in mice lacking the LIM protein LMO4 or its interacting partner Deaf-1

LMO4 belongs to a family of transcriptional regulators that comprises two zinc-binding LIM domains. LIM-only (LMO) proteins appear to function as docking sites for other factors, leading to the assembly of multiprotein complexes. The transcription factor Deaf-1/NUDR has been identified as one partner protein of LMO4. We have disrupted the Lmo4 and Deaf-1 genes in mice to define their biological function in vivo. All Lmo4 mutants died shortly after birth and showed defects within the presphenoid bone, with 50% of mice also exhibiting exencephaly. Homeotic transformations were observed in Lmo4-null embryos and newborn mice, but with incomplete penetrance. These included skeletal defects in cervical vertebrae and the rib cage. Furthermore, fusions of cranial nerves IX and X and defects in cranial nerve V were apparent in some Lmo4(-/-) and Lmo4(+/-) mice. Remarkably, Deaf-1 mutants displayed phenotypic abnormalities similar to those observed in Lmo4 mutants. These included exencephaly, transformation of cervical segments, and rib cage abnormalities. In contrast to Lmo4 nullizygous mice, nonexencephalic Deaf-1 mutants remained healthy. No defects in the sphenoid bone or cranial nerves were apparent. Thus, Lmo4 and Deaf-1 mutant mice exhibit overlapping as well as distinct phenotypes. Our data indicate an important role for these two transcriptional regulators in pathways affecting neural tube closure and skeletal patterning, most likely reflecting their presence in a functional complex in vivo.

Two promoters within the human LMO4 gene contribute to its overexpression in breast cancer cells

LMO4, a member of the LIM-only family of zinc-finger proteins, is overexpressed in more than 50% of primary breast cancers and cell lines, implying a role in the pathogenesis of this cancer. Southern blot analysis of these cell lines did not reveal amplification or rearrangement of the LMO4 gene. To investigate further the mechanism underlying LMO4 overexpression and the generation of two patterns of transcripts, we isolated genomic clones spanning the human gene. Similar to the mouse Lmo4 gene, there are two 5' noncoding exons, exon 1a and exon 1b, which we show are differentially expressed in breast epithelial cells. This reflects differential promoter usage in combination with alternative splicing. Two promoter regions were defined, one upstream of exon 1a and the other upstream of exon 1b. Both promoters exhibited strong activity in breast cancer cells, with up to 400-fold activity above basal levels. These promoters were significantly more active in T-47D and MCF-7 cells relative to SKBR3 cells, consistent with RNA levels. Thus, overexpression of the LMO4 gene in breast cancer cells reflects increased promoter activity and appears to involve aberrant activation of the second promoter in a subset of these cells.

Transcription regulator LMO4 interferes with neuritogenesis in human SH-SY5Y neuroblastoma cells

LMO4 is a transcription regulator interacting with proteins involved, among else, in tumorigenesis. Its function in the nervous system, and particularly in the adult nervous system, has however still to be elucidated. We decided to modify its expression in a neuronal model, human SH-SY5Y neuroblastoma cells, by permanent transfection of sense or anti-sense Lmo4 cDNAs. Generated clones overexpressing the Lmo4 transcript in sense orientation tended to aggregate. They showed significantly reduced average number of neurites per cell and average neuritic length per cell. The opposite was observed with clones overexpressing the anti-sense Lmo4 transcript. Furthermore, selected clones were subjected to 72 h long-term treatments with retinoic acid and phorbol ester (TPA), two biochemicals known to stimulate differentiation of non-transfected SH-SY5Y cells and other neuroblastoma cells. Neuritogenesis occurred after retinoic acid stimulation in all cases. The inhibitory effect of sense Lmo4 RNA overexpression on neuritic outgrowth was indeed prevented. The protein kinase C activator TPA could not induce neuritogenesis in SH-SY5Y cells overexpressing sense Lmo4 RNA. Thus, sense Lmo4 RNA overexpression, not Lmo4 endogenous transcription, overrides the stimulatory effect of TPA upon neuritic outgrowth. We also showed that Lmo4-dependent neuritic retraction and outgrowth correspond to altered phosphorylation of cytoskeletal proteins. Overall, Lmo4 RNA overexpression interferes with neuritic outgrowth, whereas anti-sense Lmo4 RNA expression favors neuritogenesis in SH-SY5Y cells. Consequently, changes in Lmo4 RNA expression levels might alter the rate of neuritic outgrowth in the developing and adult nervous system.

The LIM domain gene LMO4 inhibits differentiation of mammary epithelial cells in vitro and is overexpressed in breast cancer

LMO4 belongs to a family of LIM-only transcriptional regulators, the first two members of which are oncoproteins in acute T cell leukemia. We have explored a role for LMO4, initially described as a human breast tumor autoantigen, in developing mammary epithelium and breast oncogenesis. Lmo4 was expressed predominantly in the lobuloalveoli of the mammary gland during pregnancy. Consistent with a role in proliferation, forced expression of this gene inhibited differentiation of mammary epithelial cells. Overexpression of LMO4 mRNA was observed in 5 of 10 human breast cancer cell lines. Moreover, in situ hybridization analysis of 177 primary invasive breast carcinomas revealed overexpression of LMO4 in 56% of specimens. Immunohistochemistry confirmed overexpression in a high percentage (62%) of tumors. These studies imply a role for LMO4 in maintaining proliferation of mammary epithelium and suggest that deregulation of this gene may contribute to breast tumorigenesis.

Promoter function of the angiogenic inducer Cyr61gene in transgenic mice: tissue specificity, inducibility during wound healing, and role of the serum response element

The cysteine-rich angiogenic protein 61 (Cyr61) is an extracellular matrix-associated, heparin-binding protein that mediates cell adhesion, stimulates cell migration, and enhances growth factor-induced cell proliferation. Cyr61 also promotes chondrogenic differentiation and induces neovascularization. In this study, we show that a 2-kb fragment of the Cyr61 promoter, which confers growth factor-inducible expression in cultured fibroblasts, is able to drive accurate expression of the reporter gene lacZ in transgenic mice. Thus, transgene expression was observed in the developing placenta and embryonic cardiovascular, skeletal, and central and peripheral nervous systems. The sites of transgene expression are consistent with those observed of the endogenous Cyr61 gene as determined by in situ hybridization and immunohistochemistry. The transgene expression in the cardiovascular system does not require the serum response element, a promoter sequence essential for transcriptional activation of Cyr61 by serum growth factors in cultured fibroblasts. Because the serum response element contains the CArG box, a sequence element implicated in cardiovascular-specific gene expression, the nonessential nature of this sequence for cardiovascular expression of Cyr61 is unexpected. Furthermore, the Cyr61 promoter-driven lacZ expression is inducible in granulation tissue during wound healing, as is synthesis of the endogenous Cyr61 protein, suggesting a role for Cyr61 in wound healing. Consistent with this finding, purified Cyr61 protein promotes the healing of a wounded fibroblast monolayer in culture. In addition, we mapped the mouse Cyr61 gene to the distal region of chromosome 3. Together, these results define the functional Cyr61 promoter in vivo, and suggest a role of Cyr61 in wound healing through its demonstrated angiogenic activities upon endothelial cells and its chemotactic and growth promoting activities upon fibroblasts.