Lhx9 and Lhx9alpha LIM-homeodomain factors: genomic structure, expression patterns, chromosomal localization, and phylogenetic analysis

Genetically evaluating the causal role of peripheral immune cells in colorectal cancer: a two-sample Mendelian randomization study

BACKGROUND

Investigating novel therapeutic strategies for colorectal cancer (CRC) is imperative. However, there is limited research on the use of drugs to target peripheral blood immune cells in this context. To address this gap, we performed a two-sample Mendelian randomization (MR) analysis to identify potential therapeutic targets for CRC.

METHODS

We applied two-sample MR to identify the causal relationship between peripheral blood immune cells and CRC. GWAS data were obtained from the IEU OPEN GWAS project. Based on the implications from the MR results, we conducted a comprehensive database search and genetic analysis to explore potential underlying mechanisms. We predicted miRNAs for each gene and employed extensive research for potential therapeutic applications.

RESULTS

We have identified causal associations between two peripheral immune cells and colorectal cancer. Activated & resting Treg %CD4 + cell was positively associated with the risks of CRC, while DN (CD4-CD8-) %leukocyte cell exhibited a protective role in tumor progression. NEK7 (NIMA related kinase 7) and LHX9 (LIM homeobox 9) expressed in Treg cells were positively associated with CRC risks and may play a vital role in carcinogenesis.

CONCLUSIONS

This study identified causal relationship between peripheral immune cell and CRC. Treg and DN T cells were implicated to own promoting and inhibiting effects on CRC progression respectively. NEK7 and LHX9 in Treg cells were identified as potential biotarget for antitumor therapies.

Alternative LIM homeodomain splice variants are dynamically regulated at key developmental steps in vertebrates

BACKGROUND

Alternative splicing provides a broad strategy to amplify the genome. Yet how alternative splicing influences neurodevelopment or indeed which variants are translated at developmental choice points remains poorly explored. Here we focused on a gene important for neurodevelopment, the Lim homeodomain transcription factor, Lhx9. Lhx9 has two non-canonical splice variants, Lhx9a and Lhx9b which compared with the canonical variant Lhx9c have a truncated homeodomain and an alternative C-terminal sequence, suggesting that, if translated, these variants could differently impact on cellular function.

RESULTS

We created a unique antibody tool designed to selectively detect non-canonical Lhx9 variants (Lhx9ab) and used this to examine the protein expression dynamics in embryos. Lhx9ab variants were translated and dynamically expressed similarly between mouse and chicken at key developmental choice points in the spinal cord, limbs and urogenital ridge. Within the spinal cord, enrichment of Lhx9c versus Lhx9ab expression was observed during key migration and axonal projection choice points.

CONCLUSIONS

These data support the notion that the expression dynamics between canonical and non-canonical Lhx9 variants could play an important role in spinal neuron maturation. More broadly, determining the temporal dynamics of alternative protein variants is a key entry point to understand how splicing influences developmental processes. This article is protected by copyright. All rights reserved.

Diagnosis of pulmonary nodules by DNA methylation analysis in bronchoalveolar lavage fluids

BACKGROUND

Lung cancer is the leading cause of cancer-related mortality. The alteration of DNA methylation plays a major role in the development of lung cancer. Methylation biomarkers become a possible method for lung cancer diagnosis.

RESULTS

We identified eleven lung cancer-specific methylation markers (CDO1, GSHR, HOXA11, HOXB4-1, HOXB4-2, HOXB4-3, HOXB4-4, LHX9, MIR196A1, PTGER4-1, and PTGER4-2), which could differentiate benign and malignant pulmonary nodules. The methylation levels of these markers are significantly higher in malignant tissues. In bronchoalveolar lavage fluid (BALF) samples, the methylation signals maintain the same differential trend as in tissues. An optimal 5-marker model for pulmonary nodule diagnosis (malignant vs. benign) was developed from all possible combinations of the eleven markers. In the test set (57 tissue and 71 BALF samples), the area under curve (AUC) value achieves 0.93, and the overall sensitivity is 82% at the specificity of 91%. In an independent validation set (111 BALF samples), the AUC is 0.82 with a specificity of 82% and a sensitivity of 70%.

CONCLUSIONS

This model can differentiate pulmonary adenocarcinoma and squamous carcinoma from benign diseases, especially for infection, inflammation, and tuberculosis. The model's performance is not affected by gender, age, smoking history, or the solid components of nodules.

LHX9, a p53-binding protein, inhibits the progression of glioma by suppressing glycolysis

PURPOSE

LHX9 methylation has been reported in many tumors, but its functions and related mechanisms in glioma are still unknown and need to be verified.

METHODS

The protein level of LHX9 in glioma tissues was examined using western blotting and immunohistochemistry, and the functions of LHX9 in glioma cell lines were investigated using MTT and colony formation assays. In addition, the interaction between LHX9 and P53 was analyzed by immunoprecipitation, and the roles of LHX9 in cancer metabolism were explored by measuring metabolites.

RESULTS

In this study, we found that the LHX9 expression level was decreased in glioma specimens, and the upregulation of LHX9 expression inhibited the growth of glioma cells in liquid medium and on soft agar. Regarding the molecular mechanism, we found that LHX9 interacted with p53, and downregulation of LHX9 promoted the expression of the glycolysis-related enzyme PGK1 and increased the lactic acid content. By interfering with the expression of LHX9, the tumorigenicity of glioma cells was promoted, an outcome blocked by further interference with PGK1 expression.

CONCLUSION

In summary, the decreased expression of LHX9 in gliomas activates the expression of the glycolysis-related enzyme PGK1, thereby promoting the development of gliomas, suggesting that the LHX9-PGK1 signaling axis can be used as a target for the treatment of glioma.

Lhx2/9 and Etv1 Transcription Factors have Complementary roles in Regulating the Expression of Guidance Genes slit1 and sema3a

During neural network development, growing axons read a map of guidance cues expressed in the surrounding tissue that lead the axons toward their targets. In particular, Xenopus retinal ganglion axons use the cues Slit1 and Semaphorin 3a (Sema3a) at a key guidance decision point in the mid-diencephalon in order to continue on to their midbrain target, the optic tectum. The mechanisms that control the expression of these cues, however, are poorly understood. Extrinsic Fibroblast Growth Factor (Fgf) signals are known to help coordinate the development of the brain by regulating gene expression. Here, we propose Lhx2/9 and Etv1 as potential downstream effectors of Fgf signalling to regulate slit1 and sema3a expression in the Xenopus forebrain. We find that lhx2/9 and etv1 mRNAs are expressed complementary to and within slit1/sema3a expression domains, respectively. Our data indicate that Lhx2 functions as an indirect repressor in that lhx2 overexpression within the forebrain downregulates the mRNA expression of both guidance genes, and in vitro lhx2/9 overexpression decreases the activity of slit1 and sema3a promoters. The Lhx2-VP16 constitutive activator fusion reduces sema3a promoter function, and the Lhx2-En constitutive repressor fusion increases slit1 induction. In contrast, etv1 gain of function transactivates both guidance genes in vitro and in the forebrain. Based on these data, together with our previous work, we hypothesize that Fgf signalling promotes both slit1 and sema3a expression in the forebrain through Etv1, while using Lhx2/9 to limit the extent of expression, thereby establishing the proper boundaries of guidance cue expression.

Cloning, tissue distribution and methylation analyses of Lhx9 in Chinese tongue sole (Cynoglossus semilaevis)

Lhx9 is a LIM-homeodomain protein related to gonad development and sex reversal. In this study, we cloned and characterized CS-Lhx9 in the gonads of the Chinese tongue sole (Cynoglossus semilaevis). The full-length cDNA of CS-Lhx9 was 3123 bp, including an ORF of 1149 bp encoding 383 amino acids which contains two LIM domains and a homeobox domain. CS-Lhx9 transcripts were primarily observed in the testis of male and neomale at 1 yah, but nearly undetectable in the ovary. During the development of gonad, CS-Lhx9 exhibited an increasing trend and appeared to reach its peak value of expression in testis at 1 yah. In situ hybridization was performed in male and neomale gonads at 210 dah and 1 yah. The results showed strong CS-Lhx9 signals in the spermatids and spermatozoa (germ cells). Methylation level of CS-Lhx9 promoter was higher in female and lower in male and neomale gonads, showing a negative correlation with CS-Lhx9 expression.

The molecular pathways underlying early gonadal development

The body of knowledge surrounding reproductive development spans the fields of genetics, anatomy, physiology and biomedicine, to build a comprehensive understanding of the later stages of reproductive development in humans and animal models. Despite this, there remains much to learn about the bi-potential progenitor structure that the ovary and testis arise from, known as the genital ridge (GR). This tissue forms relatively late in embryonic development and has the potential to form either the ovary or testis, which in turn produce hormones required for development of the rest of the reproductive tract. It is imperative that we understand the genetic networks underpinning GR development if we are to begin to understand abnormalities in the adult. This is particularly relevant in the contexts of disorders of sex development (DSDs) and infertility, two conditions that many individuals struggle with worldwide, with often no answers as to their aetiology. Here, we review what is known about the genetics of GR development. Investigating the genetic networks required for GR formation will not only contribute to our understanding of the genetic regulation of reproductive development, it may in turn open new avenues of investigation into reproductive abnormalities and later fertility issues in the adult.

Characterization and tissue distribution of Lhx9 and Lhx9α in Chinese giant salamander Andrias davidianus

Lhx9 is an LIM (named for the first three proteins in which the domain was found, Lin-11, Isl1 and Mec-3) homeodomain protein involved in development and differentiation of the gonad. In this study, we isolated the full-length Lhx9 and Lhx9α from Andrias davidianus, detected the tissue distribution and analysed the methylation of the promoters. We identified Lhx9 of 1411 bp and Lhx9α of 1153-bp length, differing in the 3'-flanking region, encoding 399 and 330 amino acids, respectively. The Lhx9 gene was detected primarily in liver, ovary and heart with moderate expression in brain, pituitary, intestine and spleen, and low expression in the remaining examined tissues, while Lhx9α expression was high in heart, pituitary and liver, and low in spleen and stomach. Significantly higher Lhx9 expression was observed in ovary than in testis, with no differences in Lhx9α expression between testis and ovary observed. Bisulphite sequencing revealed significantly higher methylation in testis compared to ovary. The methylation level of CpG sites -733, -673, -615 and -594 exhibited significantly higher levels in testis than in ovary, which was negatively correlated with Lhx9 expression. The methylation and expression patterns suggested that promoter methylation suppressed expression of Lhx9 in A. davidianus.

Effect of sevoflurane anesthesia on the comprehensive mRNA expression profile of the mouse hippocampus

Postoperative nausea and vomiting (PONV) is a common complication after general anesthesia. Recent studies suggested that the hippocampus is involved in PONV. Hypothesising that hippocampal dopaminergic neurons are related to PONV, we examined the comprehensive mRNA profile of the hippocampus, using a sevoflurane-treated mouse model to confirm this. This study was conducted after approval from our institutional animal ethics committee, the Animal Research Center of Sapporo Medical University School of Medicine (project number: 12-033). Eight mice were assigned to two groups: a naïve group and a sevoflurane group (Sev group). In the Sev group, four mice were anesthetised with 3.5% sevoflurane for 1 hour. Subsequently, mRNA was isolated from their hippocampal cells and RNA sequencing was performed on an Illumina HiSeq 2500 platform. Mapping of the quality-controlled, filtered paired-end reads to mouse genomes and quantification of the expression levels of each gene were performed using R software. The Rtn4rl2 gene that encodes the Nogo receptor was the most up-regulated gene in the present study. The expression levels of dopamine receptor genes and the tachykinin gene were increased by sevoflurane exposure, while the genes related to serotonin receptors were not altered by sevoflurane exposure. The expression levels of LIM-homeodomain-related genes were highly down-regulated by sevoflurane. These findings suggest that sevoflurane exposure induces dopaminergic stimulation of hippocampal neurons and triggers PONV, while neuronal inflammation caused by LIM-homeodomain-related genes is down-regulated by sevoflurane.

The Lhx9-integrin pathway is essential for positioning of the proepicardial organ

The development of the vertebrate embryonic heart occurs by hyperplastic growth as well as the incorporation of cells from tissues outside of the initial heart field. Amongst these tissues is the epicardium, a cell structure that develops from the precursor proepicardial organ on the right side of the septum transversum caudal to the developing heart. During embryogenesis, cells of the proepicardial organ migrate, adhere and envelop the maturing heart, forming the epicardium. The cells of the epicardium then delaminate and incorporate into the heart giving rise to cardiac derivatives, including smooth muscle cells and cardiac fibroblasts. Here, we demonstrate that the LIM homeodomain protein Lhx9 is transiently expressed in Xenopus proepicardial cells and is essential for the position of the proepicardial organ on the septum transversum. Utilizing a small-molecule screen, we found that Lhx9 acts upstream of integrin-paxillin signaling and consistently demonstrate that either loss of Lhx9 or disruption of the integrin-paxillin pathway results in mis-positioning of the proepicardial organ and aberrant deposition of extracellular matrix proteins. This leads to a failure of proepicardial cell migration and adhesion to the heart, and eventual death of the embryo. Collectively, these studies establish a requirement for the Lhx9-integrin-paxillin pathway in proepicardial organ positioning and epicardial formation.

Integrated analysis of gene expression and DNA methylation changes induced by hepatocyte growth factor in human hepatocytes

Hepatocellular carcinoma (HCC) is the one of most common malignant tumors. The tumor microenvironment has a role in not only supporting growth and survival of tumor cells, but also triggering tumor recurrence and metastasis. Hepatocyte growth factor (HGF), one of the important growth factors in the tumor microenvironment, has an important role in angiogenesis, tumorigenesis and regeneration. However, the exact mechanism by which HGF regulates HCC initiation and development via epigenetic reprogramming has remained elusive. The present study focused on the epigenetic modification and target tumor-suppressive genes of HGF treatment in HCC. Expression profiling and DNA methylation array were performed to investigate the function of HGF and examine global genomic DNA methylation changes, respectively. Integrated analysis of gene expression and DNA methylation revealed potential tumor suppressor genes (TSGs) in HCC. The present study showed the multiple functions of HGF in tumorous and nontumorous pathways and global genomic DNA methylation changes. HGF treatment upregulated the expression of DNA methyltransferase 1 (DNMT1). Overexpression of DNMT1 in HCC patients correlated with the malignant potential and poor prognosis of HCC. Furthermore, integration analysis of gene expression and DNA methylation changes revealed novel potential tumor suppressor genes TSGs including MYOCD, PANX2 and LHX9. The present study has provided mechanistic insight into epigenetic repression of TSGs through HGF-induced DNA hypermethylation.

Alternative splicing of the LIM-homeodomain transcription factor Isl1 in the mouse retina

Islet-1 (Isl1) is a LIM-homeodomain (LIM-HD) transcription factor that functions in a combinatorial manner with other LIM-HD proteins to direct the differentiation of distinct cell types within the central nervous system and many other tissues. A study of pancreatic cell lines showed that Isl1 is alternatively spliced generating a second isoform, Isl1β, which is missing 23 amino acids within the C-terminal region. This study examines the expression of the canonical and alternative Isl1 transcripts across other tissues, in particular, within the retina, where Isl1 is required for the differentiation of multiple neuronal cell types. The alternative splicing of Isl1 is shown to occur in multiple tissues, but the relative abundance of Isl1α and Isl1β expression varies greatly across them. In most tissues, Isl1α is the more abundant transcript, but in others the transcripts are expressed equally, or the alternative splice variant is dominant. Within the retina, differential expression of the two Isl1 transcripts increases as a function of development, with dynamic changes in expression peaking at E16.5 and again at P10. At the cellular level, individual retinal ganglion cells vary in their expression, with a subset of small-to-medium sized cells expressing only the alternative isoform. The functional significance of the difference in protein sequence between the two Isl1 isoforms was also assessed using a luciferase assay, demonstrating that the alternative isoform forms a less effective transcriptional complex for activating gene expression. These results demonstrate the differential presence of the canonical and alternative isoforms of Isl1 amongst retinal ganglion cell classes. As Isl1 participates in the differentiation of multiple cell types within the CNS, the present results support a role for alternative splicing in the establishment of cellular diversity in the developing nervous system.

The Lhx9 homeobox gene controls pineal gland development and prevents postnatal hydrocephalus

Lhx9 is a member of the LIM homeobox gene family. It is expressed during mammalian embryogenesis in the brain including the pineal gland. Deletion of Lhx9 results in sterility due to failure of gonadal development. The current study was initiated to investigate Lhx9 biology in the pineal gland. Lhx9 is highly expressed in the developing pineal gland of the rat with transcript abundance peaking early in development; transcript levels decrease postnatally to nearly undetectable levels in the adult, a temporal pattern that is generally similar to that reported for Lhx9 expression in other brain regions. Studies with C57BL/6J Lhx9(-/-) mutant mice revealed marked alterations in brain and pineal development. Specifically, the superficial pineal gland is hypoplastic, being reduced to a small cluster of pinealocytes surrounded by meningeal and vascular tissue. The deep pineal gland and the pineal stalk are also reduced in size. Although the brains of neonatal Lhx9(-/-) mutant mice appear normal, severe hydrocephalus develops in about 70% of the Lhx9(-/-) mice at 5-8 weeks of age; these observations are the first to document that deletion of Lhx9 results in hydrocephalus and as such indicate that Lhx9 contributes to the maintenance of normal brain structure. Whereas hydrocephalus is absent in neonatal Lhx9(-/-)mutant mice, the neonatal pineal gland in these animals is hypoplastic. Accordingly, it appears that Lhx9 is essential for early development of the mammalian pineal gland and that this effect is not secondary to hydrocephalus.

Purkinje cell compartmentalization in the cerebellum of the spontaneous mutant mouse dreher

The cerebellar morphological phenotype of the spontaneous neurological mutant mouse dreher (Lmx1a(dr-J)) results from cell fate changes in dorsal midline patterning involving the roof plate and rhombic lip. Positional cloning revealed that the gene Lmx1a, which encodes a LIM homeodomain protein, is mutated in dreher, and is expressed in the developing roof plate and rhombic lip. Loss of Lmx1a causes reduction of the roof plate, an important embryonic signaling center, and abnormal cell fate specification within the embryonic cerebellar rhombic lip. In adult animals, these defects result in variable, medial fusion of the cerebellar vermis and posterior cerebellar vermis hypoplasia. It is unknown whether deleting Lmx1a results in displacement or loss of specific lobules in the vermis. To distinguish between an ectopic and absent vermis, the expression patterns of two Purkinje cell-specific compartmentation antigens, zebrin II/aldolase C and the small heat shock protein HSP25 were analyzed in dreher cerebella. The data reveal that despite the reduction in volume and abnormal foliation of the cerebellum, the transverse zones and parasagittal stripe arrays characteristic of the normal vermis are present in dreher, but may be highly distorted. In dreher mutants with a severe phenotype, zebrin II stripes are fragmented and distributed non-symmetrically about the cerebellar midline. We conclude that although Purkinje cell agenesis or selective Purkinje cell death may contribute to the dreher phenotype, our data suggest that aberrant anlage patterning and granule cell development lead to Purkinje cell ectopia, which ultimately causes abnormal cerebellar architecture in dreher.

Structural basis for partial redundancy in a class of transcription factors, the LIM homeodomain proteins, in neural cell type specification

Combinations of LIM homeodomain proteins form a transcriptional "LIM code" to direct the specification of neural cell types. Two paralogous pairs of LIM homeodomain proteins, LIM homeobox protein 3/4 (Lhx3/Lhx4) and Islet-1/2 (Isl1/Isl2), are expressed in developing ventral motor neurons. Lhx3 and Isl1 interact within a well characterized transcriptional complex that triggers motor neuron development, but it was not known whether Lhx4 and Isl2 could participate in equivalent complexes. We have identified an Lhx3-binding domain (LBD) in Isl2 based on sequence homology with the Isl1(LBD) and show that both Isl2(LBD) and Isl1(LBD) can bind each of Lhx3 and Lhx4. X-ray crystal- and small-angle x-ray scattering-derived solution structures of an Lhx4·Isl2 complex exhibit many similarities with that of Lhx3·Isl1; however, structural differences supported by mutagenic studies reveal differences in the mechanisms of binding. Differences in binding have implications for the mode of exchange of protein partners in transcriptional complexes and indicate a divergence in functions of Lhx3/4 and Isl1/2. The formation of weaker Lhx·Isl complexes would likely be masked by the availability of the other Lhx·Isl complexes in postmitotic motor neurons.

Characterization of a novel human HMBOX1 splicing variant lacking the homeodomain and with attenuated transcription repressor activity

We previously identified the human HMBOX1 (homeobox containing 1) gene, which represents a distinct group of HNF transcription factors, and is a potential transcription repressor with highly expression in pancreas. In our present work, we found that there exists a splicing variant of HMBOX1, designated HMBOX1b. Compared to HMBOX1, HMBOX1b encodes a 304 amino acids protein that shares the N-terminal region but has no homeodomain and the C-terminal region because of an alternative exon 7 which results in reading frame shifting. Unlike the highly pancreatic expression of HMBOX1, HMBOX1b was ubiquitous expressed in all human tissues detected by RT-PCR. Immunofluorescence staining showed that HMBOX1b accumulated in both cytoplasm and nucleus, and transcriptional reporter assays indicated that HMBOX1b only retained faint transcriptional repressive activity. Taken together, our findings suggest a distinct role of HMBOX1b, and the control of mRNA splicing might be involved in homeobox genes regulation.

Aberrant methylation and reduced expression of LHX9 in malignant gliomas of childhood

High-grade gliomas (HGGs) of childhood represent approximately 7% of pediatric brain tumors. They are highly invasive tumors and respond poorly to conventional treatments in contrast to pilocytic astrocytomas, which usually are well demarcated and frequently can be cured by surgery. The molecular events for this clinical relevant finding are only partially understood. In the current study, to identify aberrantly methylated genes that may be involved in the tumorigenesis of pediatric HGGs, we performed a microarray-based differential methylation hybridization approach and found frequent hypermethylation of the LHX9 (human Lim-homebox 9) gene encoding a transcription factor involved in brain development. Bisulfite genomic sequencing and combined bisulfite restriction analysis showed that HGGs were frequently methylated at two CpG-rich LHX9 regions in comparison to benign, nondiffuse pilocytic astrocytomas and normal brain tissues. The LHX9 hypermethylation was associated with reduced messenger RNA expression in pediatric HGG samples and corresponding cell lines. This epigenetic modification was reversible by pharmacological inhibition (5-aza-2'-deoxycytidine), and reexpression of LHX9 transcript was induced in pediatric glioma cell lines. Exogenous expression of LHX9 in glioma cell lines did not directly affect cell proliferation and apoptosis but specifically inhibited glioma cell migration and invasion in vitro, suggesting a possible implication of LHX9 in the migratory phenotype of HGGs. Our results demonstrate that the LHX9 gene is frequently silenced in pediatric malignant astrocytomas by hypermethylation and that this epigenetic alteration is involved in glioma cell migration and invasiveness.

Developmental expression of apterous/Lhx2/9 in the sepiolid squid Euprymna scolopes supports an ancestral role in neural development

The transcription factors Apterous/Lhx2/9 play many pivotal roles in the development of protostomes and deuterostomes, most notably limb patterning, eye morphogenesis, and brain development. Full-length apterous/lhx2/9 homologs have been isolated from several invertebrate species, but hitherto not from a lophotrochozoan. Here, we report the isolation, characterization, and spatio-temporal expression of apterous in the sepiolid squid Euprymna scolopes. The isolated composite cDNA encodes a hypothetical protein of 448 amino acid residues with a typical LIM-homeodomain (LIM-HD) structure and the greatest overall sequence similarity to vertebrate Lhx2/9 proteins. The Euprymna scolopes apterous (Es-ap) expression patterns provided no indication of a role in the early dorso/ventral patterning or growth of the arm crown that showed expression only in two ventral cords running in parallel inside the arms and tentacles and at the base of the suckers, a region rich in nerve endings and chemosensory neurons. The Es-ap hybridization signal was also conspicuous in the eyes, olfactory organs, optic lobes, and in several lobes of the supraesophageal mass, among these the olfactory and vertical lobes, and paravertical bodies. The observed expression patterns suggest gene involvement in eye morphogenesis and neural wiring of sensory structures, including those for olfaction and vision.

FGF receptor dependent regulation of Lhx9 expression in the developing nervous system

LIM-homeodomain (LIM-hd) proteins form a multifunctional family of transcription factors that plays critical roles in the development of progenitor and post-mitotic cells. Considerable work has focused on what regulates their expression post-mitotically in the spinal cord. However, little is known about what regulates LIM-hd genes at earlier developmental stages. To address this question, we explored the role of fibroblast growth factor (FGF) signalling in regulating the expression of a Xenopus laevis Lhx9 orthologue (XLhx9). XLhx9 is first expressed in the eye field and hindbrain, and when FGF receptor (FGFR) activation was inhibited prior to its onset, both brain and eye field expression was diminished. However, when FGFRs were inhibited after XLhx9 onset, retinal expression remained strong and brain expression was again diminished. These data suggest that while FGF signalling initiates and maintains brain XLhx9 expression, in the eye primordium the requirement of FGFs for expression is rapidly lost.

GATA4/FOG2 transcriptional complex regulates Lhx9 gene expression in murine heart development

BACKGROUND

GATA4 and FOG2 proteins are required for normal cardiac development in mice. It has been proposed that GATA4/FOG2 transcription complex exercises its function through gene activation as well as repression; however, targets of GATA4/FOG2 action in the heart remain elusive.

RESULTS

Here we report identification of the Lhx9 gene as a direct target of the GATA4/FOG2 complex. We demonstrate that the developing mouse heart normally expresses truncated isoforms of Lhx9 - Lhx9alpha and Lhx9beta, and not the Lhx9-HD isoform that encodes a protein with an intact homeodomain. At E9.5 Lhx9alpha/beta expression is prominent in the epicardial primordium, septum transversum while Lhx9-HD is absent from this tissue; in the E11.5 heart LHX9alpha/beta-positive cells are restricted to the epicardial mesothelium. Thereafter in the control hearts Lhx9alpha/beta epicardial expression is promptly down-regulated; in contrast, mouse mutants with Fog2 gene loss fail to repress Lhx9alpha/beta expression. Chromatin immunoprecipitation from the E11.5 hearts demonstrated that Lhx9 is a direct target for GATA4 and FOG2. In transient transfection studies the expression driven by the cis-regulatory regions of Lhx9 was repressed by FOG2 in the presence of intact GATA4, but not the GATA4ki mutant that is impaired in its ability to bind FOG2.

CONCLUSION

In summary, the Lhx9 gene represents the first direct target of the GATA4/FOG2 repressor complex in cardiac development.

Sexual dimorphism of gonadal development

Sexual dimorphism is a term describing morphological differences between the sexes, but is often extended to include all differences observed between females and males. Sex differentiation in vertebrates is by definition sexually dimorphic and starts at the level of the sex chromosomes. In this review the sexual dimorphism of gonadal differentiation is discussed, with a focus on human development. In the embryo, the indifferent gonadal anlagen harbours four different cell lineages with bipotential fates dependent on the sex of the individual. The different paths taken by these cell lineages in male and female development are reviewed, along with other sexually dimorphic features of gonadal development. These include sex-determining genes, timing of events, dependence on germ cells, spatial organization of stromal cells, steroidogenic cells types, and other aspects.

Cloning and functional analysis of hypothalamic homeobox gene Bsx1a and its isoform, Bsx1b

The hypothalamus is a key regulatory unit of the neuroendocrine system and plays an essential role in energy balance and reproduction. Despite its important role, the molecular mechanisms underlying hypothalamic development are not fully understood. Here, we report molecular analyses of a newly identified murine homeobox gene, Bsx/Bsx1a, that is expressed in the developing and postnatal hypothalamus. We demonstrate that BSX1A is a DNA binding protein and a transcriptional activator. Transcriptional reporter assays identified the C-terminal region of BSX1A as an activation domain. We have isolated an alternative splice form of Bsx1a, designated Bsx1b, which retains the N-terminal region but lacks the homeodomain. Analyses of subcellular localization using transfected cell lines revealed that BSX1A and BSX1B localize in the nuclei and cytoplasm, respectively. Immunohistochemical analyses suggested that both BSX1A and BSX1B are expressed in the neonatal hypothalamus. Taking these data together, we propose that alternative RNA splicing is involved in hypothalamic development/function.

Gene expression analysis of TFII-I modulated genes in mouse embryonic fibroblasts

TFII-I is a founding member of a family of helix-loop-helix transcription factors involved in modulation of genes through interaction with various nuclear factors and chromatin remodeling complexes. Recent studies indicate that TFII-I performs important function in cell physiology and mouse embryogenesis. In order to understand its molecular role, TFII-I was overexpressed in primary mouse embryonic fibroblasts (MEFs) and alterations in gene expression were monitored with a mouse 16 K oligonucleotide microarray. These studies allowed us to identify genes that lie downstream of TFII-I-dependent pathways. Among the modulated candidates were genes involved in the immunity response, catalytic activity, signaling pathways and transcriptional regulation. Expression of several candidates including those for the interferon-stimulated protein (G1p2), small inducible cytokine A7 (Ccl7), ubiquitin-conjugating enzyme 8 (Ube2l6), cysteine-rich protein (Csrp2) and Drosophila delta-like 1 homolog (Dlk1) were confirmed by real-time PCR. The obtained results suggest that TFII-I participates in multiple signaling and regulatory pathways in MEFs.

LIM-homeodomain genes in mammalian development and human disease

The human and mouse genomes each contain at least 12 genes encoding LIM homeodomain (LIM-HD) transcription factors. These gene regulatory proteins feature two LIM domains in their amino termini and a characteristic DNA binding homeodomain. Studies of mouse models and human patients have established that the LIM-HD factors are critical for the development of specialized cells in multiple tissue types, including the nervous system, skeletal muscle, the heart, the kidneys, and endocrine organs such as the pituitary gland and the pancreas. In this article, we review the roles of the LIM-HD proteins in mammalian development and their involvement in human diseases.

Fgf signaling is required for zebrafish tooth development

We have investigated fibroblast growth factor (FGF) signaling during the development of the zebrafish pharyngeal dentition with the goal of uncovering novel roles for FGFs in tooth development as well as phylogenetic and topographic diversity in the tooth developmental pathway. We found that the tooth-related expression of several zebrafish genes is similar to that of their mouse orthologs, including both epithelial and mesenchymal markers. Additionally, significant differences in gene expression between zebrafish and mouse teeth are indicated by the apparent lack of fgf8 and pax9 expression in zebrafish tooth germs. FGF receptor inhibition with SU5402 at 32 h blocked dental epithelial morphogenesis and tooth mineralization. While the pharyngeal epithelium remained intact as judged by normal pitx2 expression, not only was the mesenchymal expression of lhx6 and lhx7 eliminated as expected from mouse studies, but the epithelial expression of dlx2a, dlx2b, fgf3, and fgf4 was as well. This latter result provides novel evidence that the dental epithelium is a target of FGF signaling. However, the failure of SU5402 to block localized expression of pitx2 suggests that the earliest steps of tooth initiation are FGF-independent. Investigations of specific FGF ligands with morpholino antisense oligonucleotides revealed only a mild tooth shape phenotype following fgf4 knockdown, while fgf8 inhibition revealed only a subtle down-regulation of dental dlx2b expression with no apparent effect on tooth morphology. Our results suggest redundant FGF signals target the dental epithelium and together are required for dental morphogenesis. Further work will be required to elucidate the nature of these signals, particularly with respect to their origins and whether they act through the mesenchyme.

Lhx9andLhx9α: Differential Biochemical Properties and Effects on Neuronal Differentiation

The Lhx9 LIM-homeodomain transcription factor and its truncated isoform Lhx9alpha are generated by alternative splicing of the Lhx9 gene. Here we investigated the differential functional properties of these two isoforms. Lhx9alpha, which lacks parts of the homeodomain, was unable to bind DNA in EMSA experiments, but was able to associate with CLIM cofactors in GST pull-down assays. In transfection experiments in PC12 cells, Lhx9alpha fusion constructs systematically showed a nuclear localization, as opposed to Lhx9 fusion constructs, which also localized to the cytoplasm. Moreover, Lhx9 increased NGF-induced neuronal differentiation of PC12 cells. Lhx9alpha, on the other hand, did not significantly increase neuronal differentiation but had an effect on the morphology of PC12 cells. Finally, as tested by RT-PCR experiments on transfected PC12 cells, Lhx9 was not able to induce the transcription of Lhx9alpha. Our results show significantly different functional properties for Lhx9 and Lhx9alpha, and suggest that Lhx9alpha can compete away limiting amounts of nuclear CLIM cofactors. Thus, Lhx9 and Lhx9alpha isoforms could be implicated in regulating various aspects of neuronal differentiation.

Different patterns of anti-Müllerian hormone expression, as related to DMRT1, SF-1, WT1, GATA-4, Wnt-4, and Lhx9 expression, in the chick differentiating gonads

In mammals, anti-Müllerian hormone (AMH) is produced by Sertoli cells from the onset of testicular differentiation and by granulosa cells after birth. In birds, AMH starts to be expressed in indifferent gonads of both sexes at a similar level and is later up-regulated in males. We previously demonstrated that, unlike in mammals, the onset of AMH expression occurs in chick embryo in the absence of SOX9. We looked for potential factors that might be involved in regulating AMH expression at different stages of chick gonad differentiation by comparing its expression pattern in embryos and young chicken with that of DMRT1, SF-1, WT1, GATA-4, Wnt-4, and Lhx9, by in situ hybridization. The results allowed us to distinguish different phases. (1) In indifferent gonads of both sexes, AMH is expressed in dispersed medullar cells. SF-1, WT1, GATA-4, Wnt-4, and DMRT1 are transcribed in the same region of the gonads, but none of these factors has an expression strictly coincident with that of AMH. Lhx9 is present only in the cortical area. (2) After this period, AMH is up-regulated in male gonads. The up-regulation is concomitant with the beginning of SOX9 expression and a sex dimorphic level of DMRT1 transcripts. It is followed by the aggregation of the AMH-positive cells (Sertoli cells) into testicular cords in which AMH is coexpressed with DMRT1, SF-1, WT1, GATA-4, and SOX9. (3) In the females, the low level of dispersed medullar AMH expression is conserved. With development of the cortex in the left ovary, cells expressing AMH accumulate in the juxtacortical part of the medulla, whereas they remain dispersed in the right ovary. At this stage, AMH expression is not strictly correlated with any of the studied factors. (4) After hatching, the organization of left ovarian cortex is characterized by the formation of follicles. Follicular cells express AMH in conjunction with SF-1, WT1, and GATA-4 and in the absence of SOX9, as in mammals. In addition, they express Lhx9 and Wnt-4, the latter being also found in the oocytes. (5) Moreover, unlike in mammals, the chicken ovary retains a dispersed AMH expression in cortical interstitial cells between the follicles, with no obvious correlation with any of the factors studied. Thus, the dispersed type of AMH expression in indifferent and female gonads appears to be bird-specific and not controlled by the same factors as testicular or follicular AMH transcription.

The LIM-homeodomain gene family in the developing Xenopus brain: conservation and divergences with the mouse related to the evolution of the forebrain

A comparative analysis of LIM-homeodomain (LIM-hd) expression patterns in the developing stage 32 Xenopus brain is presented. x-Lhx2, x-Lhx7, and x-Lhx9 were isolated and their expression, together with that of x-Lhx1 and x-Lhx5, was analyzed in terms of prosomeric brain development and LIM-hd combinatorial code and compared with mouse expression data. The results show an almost complete conservation of expression patterns in the diencephalon. The Lhx1/5 and Lhx2/9 subgroups label the pretectum/ventral thalamus/zona limitans versus the dorsal thalamus, respectively, in alternating stripes of expression in both species. Conversely, strong divergences in expression patterns are observed between the telencephalon of the two species for Lhx1/5 and Lhx2/9. Lhx7 exhibits particularly conservative patterns and is proposed as a medial ganglionic eminence marker. The conservation of diencephalic segments is proposed to mirror the conservative nature of diencephalic structures across vertebrates. In contrast, the telencephalic divergences are proposed to reflect the emergence of significant novelty in the telencephalon (connectivity changes) at the anamniote/amniote transition. Moreover, the data allow the new delineation of pallial and subpallial domains in the developing frog telencephalon, which are compared with mouse subdivisions. In the pallium, the mouse combinatorial expression of LIM-hd is notably richer than in the frog, again possibly reflecting evolutionary changes in cortical connectivity.