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PubMed2006

A role for GATA factors in Xenopus gastrulation movements.

Gastrulation movements in Xenopus laevis are becoming increasingly well characterised, however the molecular mechanisms involved are less clear. Active migration of the leading edge mesendoderm across the fibronectin-coated blastocoel roof is necessary for further development of tissues such as head mesoderm, heart, blood and liver. The zinc finger transcription factors GATA4 and GATA6 are expressed in this migratory tissue during gastrulation, but their role here is unknown. This study further characterises the expression of GATA4 and 6 during gastrulation, and investigates their function in migratory behaviour. Gain-of-function experiments with these GATA factors induce cell spreading, polarisation and migration in non-motile presumptive ectoderm cells. Expression of a dominant-interfering form of GATA6, which inhibits transactivation of GATA targets, severely impairs the ability of dorsal leading edge mesendoderm to spread and translocate on fibronectin. Mosaic inhibition of GATA activity indicates that GATA factors function cell autonomously to induce cell spreading and movement in dorsal mesendoderm. Knockdown of specific GATA factors using anti-sense morpholinos indicates that GATA4 and GATA6 both contribute to dorsal mesendoderm migration in vitro. GATA4 and GATA6 are known to be involved in cell-specification of mesoderm and endoderm-derived tissues, but this is the first description of an additional role for these factors in cell migration.

Activins↗

PubMed2006

NtLRP1, a tobacco leucine-rich repeat gene with a possible role as a modulator of the hypersensitive response.

Plant defense responses against pathogens often involve the restriction of the pathogen to its site of penetration achieved through the combined effects of the hypersensitive response (HR) and its tightly connected localized acquired resistance (LAR). The tobacco DD9-3 expressed sequence tag was previously isolated from a screen designed to isolate genes induced early during the HR, thus potentially involved in the induction/regulation of the HR or LAR. Translation of the open reading frame of DD9-3 revealed a leucine-rich repeat (LRR) domain highly homologous with the receptor domain of a receptor kinase, suggesting a potential function in signaling pathways. The full-length cDNA was cloned. It encodes a small (232 amino acids) LRR protein, designated Nicotiana tabacum leucine-rich protein 1 (NtLRP1), containing a signal peptide, four leucine zipper repeats, five LRR repeats, and a C-terminal domain rich in proline. NtLRP1 expression is induced early during the HR initiated by elicitins, Ralstonia solanacearum, or Tobacco mosaic virus. NtLRP1 coupled with the green fluorescent protein localizes to the endoplasmic reticulum (ER). Loss-of-function through virus-induced gene silencing or through RNA interference did not modify the elicitin-induced HR or LAR. Gain-of-function experiments through transient Agrobacterium tumefaciens-mediated NtLRP1 expression in tobacco leaves caused the suppression of the HR induced by 2 nM elicitin and delayed the HR when the elicitin was applied at higher concentrations. The results suggest that NtLRP1 acts as a modulator of the HR and that retention in the ER is essential for its function.

Amino Acid Sequence↗

PubMed1996

Dual function of the region-specific homeotic gene spalt during Drosophila tracheal system development.

We report that the region-specific homeotic gene spalt affects the Drosophila tracheal system at two different stages of embryonic development. Both lack-of-function and gain-of-function experiments show that blastodermal spalt activity restricts tracheal development to 10 bilaterally positioned pairs of tracheal placodes in the trunk region by repressing placode formation in parasegments 2, 3 and 14. The results suggest that the activity of the zinc-finger type transcription factor encoded by spalt suppresses the molecular pathway that establishes tracheal development. spalt function is also necessary for the directed migration of the dorsal trunk cells, a distinct subset of tracheal cells. This process is a prerequisite for the formation of the dorsal trunk generated by fusion of adjacent tracheal metameres into a common tubular structure. The directed cell migration, in which spalt gene function participates, seems to be independent of branch fusion and general tracheal cell migration processes.

Animals↗

PubMed2004

Neural induction in Xenopus: requirement for ectodermal and endomesodermal signals via Chordin, Noggin, beta-Catenin, and Cerberus.

The origin of the signals that induce the differentiation of the central nervous system (CNS) is a long-standing question in vertebrate embryology. Here we show that Xenopus neural induction starts earlier than previously thought, at the blastula stage, and requires the combined activity of two distinct signaling centers. One is the well-known Nieuwkoop center, located in dorsal-vegetal cells, which expresses Nodal-related endomesodermal inducers. The other is a blastula Chordin- and Noggin-expressing (BCNE) center located in dorsal animal cells that contains both prospective neuroectoderm and Spemann organizer precursor cells. Both centers are downstream of the early beta-Catenin signal. Molecular analyses demonstrated that the BCNE center was distinct from the Nieuwkoop center, and that the Nieuwkoop center expressed the secreted protein Cerberus (Cer). We found that explanted blastula dorsal animal cap cells that have not yet contacted a mesodermal substratum can, when cultured in saline solution, express definitive neural markers and differentiate histologically into CNS tissue. Transplantation experiments showed that the BCNE region was required for brain formation, even though it lacked CNS-inducing activity when transplanted ventrally. Cell-lineage studies demonstrated that BCNE cells give rise to a large part of the brain and retina and, in more posterior regions of the embryo, to floor plate and notochord. Loss-of-function experiments with antisense morpholino oligos (MO) showed that the CNS that forms in mesoderm-less Xenopus embryos (generated by injection with Cerberus-Short [CerS] mRNA) required Chordin (Chd), Noggin (Nog), and their upstream regulator beta-Catenin. When mesoderm involution was prevented in dorsal marginal-zone explants, the anterior neural tissue formed in ectoderm was derived from BCNE cells and had a complete requirement for Chd. By injecting Chd morpholino oligos (Chd-MO) into prospective neuroectoderm and Cerberus morpholino oligos (Cer-MO) into prospective endomesoderm at the 8-cell stage, we showed that both layers cooperate in CNS formation. The results suggest a model for neural induction in Xenopus in which an early blastula beta-Catenin signal predisposes the prospective neuroectoderm to neural induction by endomesodermal signals emanating from Spemann's organizer.

Animals↗

PubMed1986

A model of transient myocardial dysfunction in conscious dogs. Regional shortening in the presence of impaired coronary flow reserve and treadmill exercise.

An experimental model of treadmill exercise-induced regional myocardial dysfunction was developed in conscious dogs to mimic exertional angina pectoris in man. Twenty mongrel dogs, trained to run on a treadmill, were chronically instrumented with a miniature pressure transducer in the left ventricle and a hydraulic occluder placed around the circumflex branch of the left coronary artery. Two pairs of piezoelectric crystals for sonomicrometry were implanted subendocardially to measure regional myocardial function. Experiments were started 1 week after surgery. In the first group of ten dogs exercise with constant work load of 10 km/hr and 10% elevation during partial left coronary artery stenosis, induced by external filling of the occluder, produced comparable episodes of regional dysfunction in the left coronary artery area during five subsequent treadmill runs and recovery of function after each run. The second group of ten dogs, exercised with left coronary artery stenosis and increasing working load, exhibited minimal regional dysfunction in the left coronary artery area while running at 6 km/hr and 6% elevation, but maximal regional dysfunction during peak exercise (10 km/hr and 10% elevation). This load dependency and recovery of function after the runs was demonstrated during five identical consecutive exercise cycles. This model, in contrast to those using ameroid constrictors, enables various drugs to be tested in a single instrumented dog over a period of several weeks.

Angina Pectoris↗

PubMed1993

Interaction between the tobacco DNA-binding activity CBF and the cyt-1 promoter element of the Agrobacterium tumefaciens T-DNA gene T-CYT correlates with cyt-1 directed gene expression in multiple tobacco tissue types.

A novel DNA-binding activity, designated CBF, has been identified in nuclear extracts from tobacco leaf, stem and root tissue. CBF interacts specifically with a 30 bp promoter fragment, referred to as cyt-1, of the Agrobacterium tumefaciens T-DNA cytokinin (T-cyt) gene. The T-cyt promoter, although of bacterial origin is active in planta and the 30 bp cyt-1 element is located within a region that is essential for T-cyt promotor activity in leaf, stem and root cells of tobacco plants. Gel retardation assays using different synthetic oligonucleotides and methylation interference experiments pinpointed the binding site of CBF to a GC-rich sequence ATGCCCCACA within the cyt-1 element. Site-directed mutagenesis of the CBF binding site within the T-cyt promoter by using PCR resulted in an almost complete loss of T-cyt promoter activity in transgenic tobacco plants. In a gain-of-function experiment a hexamer of cyt-1 was shown to be able to confer leaf, stem and root expression when fused upstream of a TATA box containing -55 derivative of the T-cyt promoter. A mutant cyt-1 hexamer, defective in CBF binding, did not show activity above background levels. These results indicate that binding of CBF to the cyt-1 element is required for cyt-1 directed gene expression, suggesting that CBF might act as a transcriptional activator. Apart from the ASF-1 binding site of the CaMV 35S promoter, which is also present in the T-DNA nopaline and octopine synthase genes, the cyt-1 element is the only other identified element reported until now that in combination with a TATA box is sufficient to drive gene expression in multiple tobacco tissue types.

Agrobacterium tumefaciens↗

PubMed2006

Cooperative action of Sox9, Snail2 and PKA signaling in early neural crest development.

In neural crest formation, transcription factors, such as group E Sox and Snail1/Snail2 (Slug) regulate subsequent epithelial-mesenchymal transition (EMT) and migration. In particular, Sox9 has a strong effect on neural crest formation, EMT and differentiation of crest-derived cartilages in the cranium. It remains unclear, however, how Sox9 functions in these events, and how Sox9 activity is regulated. In this study, our gain-of-function and loss-of-function experiments reveal that Sox9 is essential for BMP signal-mediated induction of Snail2 and subsequent EMT in avian neural crest. We also show that Snail2 activates the Snail2 promoter, although Snail family proteins have been known as a repressor. Consistently, Sox9 directly activates the Snail2 promoter in synergy with, and through a direct binding to, Snail2. Finally, functions of these transcription factors in neural crest cells are enhanced by PKA signaling.

Animals↗

PubMed1998

Wilms' tumor suppressor gene (WT1) as a target gene of SRY function in a mouse ES cell line transfected with SRY.

With the aim of identifying the gene(s) located downstream from SRY, we transfected an ES cell line with XX karyotype, TMA-18, with a Sry DNA construct and established cell lines, TS18-1 and TS18-2, where the transfected Sry was expressed in the functional linear mRNA form. Among the five potential SRY-target genes examined, i.e., MIS, SF1, P450arom, Sox9 and WT1, only the expression of WT1 was induced de novo by the unscheduled expression of Sry in the transfected cell lines. No clear indication of Sry-induced enhancement of Sox9 expression was obtained in the present series of experiments. Function of a yet unidentified gene(s) located on the Y chromosome might be needed for the up-regulation of Sox 9 expression which takes place during the development of male gonads. Quantitative RT-PCR analysis of the patterns of WT1 expression in developing fetal gonads revealed that although both male and female fetal gonads express WT1, male gonads invariably expressed WT1 mRNA at higher levels than female ones after the Sry expression. Immunohistochemical analysis of the male fetal gonads between 10.5 and 13.5 dpc demonstrated the presence of strong WT1 immunoreactivity in Sertoli cells of the primordial testes. Suggestions were made in the past indicating that both SF1 and WT1 proteins might be active in a common pathway upstream from Sry. Our results showed that WT1 is located downstream, rather than upstream from Sry and behaves independently from SF1. Analysis using an appropriate in vitro system will be essential to understand the molecular mechanisms of SRY action within cells.

Animals↗

PubMed2005

Simultaneous perfusion and blood-oxygenation-level-dependent measurements using single-shot interleaved z-shim echo-planar imaging.

Single-shot interleaved z-shim EPI (SSIZS-EPI) was extended to a simultaneous perfusion and blood-oxygenation-level-dependent (BOLD) imaging technique that reduces susceptibility-induced signal loss while preserving rapid image acquisition. Experiments on human brains showed that images acquired with this technique had improved signal-to-noise ratio in the inferior prefrontal, meso-, and lateral-temporal lobes compared with a conventional EPI. Perfusion maps obtained from the SSIZS-EPI images at resting state illustrated substantial signal recovery in these brain areas. Perfusion and BOLD images collected with a sensorimotor paradigm demonstrated the feasibility of the technique to simultaneously measure cerebral blood flow and blood oxygenation signals associated with brain activation. Functional experiments with a neuropsychiatric paradigm showed increased brain activities in the periamygdalar regions in both perfusion and BOLD maps, consistent with a previous H(2) (15)O PET study. The proposed technique, with its advantages of reducing susceptibility artifacts and fast scanning speed, would be useful for obtaining more reliable measurements of functional signals, particularly in the brain regions with field inhomogeneities.

Artifacts↗

PubMed2026

Dietary Polyphenol Acteoside-Related Molecular Signatures in Clear Cell Renal Cell Carcinoma: Multi-Omics Profiling and Functional Validation of IMPDH1.

Clear cell renal cell carcinoma (ccRCC) is characterized by substantial metabolic and molecular heterogeneity, but the disease-relevant programs associated with acteoside, a dietary polyphenol, remain poorly understood. We integrated predicted acteoside targets with bulk, single-cell, and spatial transcriptomic data from ccRCC and combined molecular subtyping with cross-cohort machine-learning analysis. Acteoside-related signatures were preferentially enriched in malignant compartments and increased with tumor grade and stage. Consensus clustering identified two molecular subtypes with distinct biological and clinical features. C1 was associated with immune activation, metabolic activity, and more favorable survival, whereas C2 showed greater genomic instability, reduced renal epithelial differentiation, and poorer outcomes. We further benchmarked multiple machine-learning strategies and established a 10-gene prognostic model that retained predictive performance across independent cohorts, with IMPDH1 emerging as the strongest risk-associated feature. Functional experiments confirmed the biological relevance of IMPDH1: its knockdown suppressed ccRCC cell proliferation, DNA synthesis, colony formation, and migration, whereas overexpression produced the opposite effects. Together, these findings indicate that acteoside-related molecular signatures capture clinically relevant heterogeneity in ccRCC and provide a framework for linking dietary-polyphenol-related molecular space with tumor biology. The identification and functional validation of IMPDH1 further highlight its potential importance in ccRCC progression.

IMPDH1↗

PubMed2026

Non-syndromic premature ovarian insufficiency associated with monoallelic LIG4 mutation via haploinsufficiency.

BACKGROUND: Premature ovarian insufficiency (POI) is a heterogeneous reproductive disorder, with genetic factors, particularly defects in DNA damage response pathways, increasingly implicated in its pathogenesis. DNA ligase IV (LIG4) is a key enzyme in the non-homologous end joining (NHEJ) pathway responsible for repairing DNA double-strand breaks (DSBs). However, its role in non-syndromic POI remains unclear. This study aimed to investigate the potential contribution of LIG4 variants to non-syndromic POI. RESULTS: Whole-exome sequencing identified a heterozygous frameshift variant in LIG4 (c.1271_1275del) in a three-generation Han Chinese family with non-syndromic POI, which co-segregated with affected individuals. AlphaFold-based structural modeling predicted truncation of the C-terminal XRCC4 interaction region. Functional experiments demonstrated that the mutant LIG4 protein showed reduced stability and was predominantly mislocalized to the cytoplasm of cells. In ovarian KGN cells, LIG4 depletion reduced cell viability, induced stress-associated cellular senescence, and impaired DNA damage repair capacity. In LIG4 knockout 293T cells, co-transfection of wild-type and mutant constructs revealed dose-dependent functional impairment, resulting in increased apoptosis under basal conditions and after phleomycin induced DNA damage, together with delayed repair of DSBs. Reanalysis of public single-cell RNA sequencing data further showed stage specific upregulation of LIG4 during oocyte maturation. Co-expression network analysis revealed enrichment in the Fanconi anemia pathway, phosphatidylinositol 3-kinase signaling pathway, and glycan metabolism. CONCLUSIONS: Our findings suggest that monoallelic LIG4 mutations may represent a potential genetic etiology for non-syndromic POI with sex-limited penetrance. While further validation in more physiologically relevant models is warranted, our data indicate that LIG4 haploinsufficiency may impair DSB repair and disrupt molecular pathways crucial for oocyte maturation and survival, highlighting a potential role of the NHEJ pathway in maintaining human ovarian function.

Humans↗

PubMed2006

Assessment of pulmonary function after lobectomy for lung cancer--upper lobectomy might have the same effect as lung volume reduction surgery.

OBJECTIVE: Lung volume reduction surgery (LVRS) in well-selected patients with severe emphysema results in postoperative improvement in symptoms and pulmonary function. Experience with LVRS suggests that predicted postoperative FEV(1.0) may be underestimated after lobectomy in patients with lung cancer and emphysema. As most of the patients with lung cancer have more or less emphysematous changes in the lungs, we assumed that lobectomy would achieve the same effect as LVRS even in patients without chronic obstructive pulmonary disease on the pulmonary function test. We assessed changes in pulmonary function in terms of 'volume reduction effect' after lobectomy for lung cancer. METHODS: Forty-three patients underwent right upper lobectomy (RUL), 38 patients left upper lobectomy (LUL), 39 patients right lower lobectomy (RLL), and 38 patients left lower lobectomy (LLL). Pulmonary function tests were performed preoperatively and 6 months to 1 year after surgery. RESULTS: Percent change in FEV(1.0) after lobectomy was -6.9+/-16.1% in RUL group, -11.2+/-16.9% in LUL group, -14.7+/-9.8% in RLL group, and -12.8+/-9.5% in LLL group. We evaluated the correlation between a preoperative FEV(1.0)% of predicted and percentage change in FEV(1.0) after lobectomy. There were no significant relationships between these variables in RLL or LLL group. In contrast, there were significant negative relationships between these variables in RUL and LUL groups. Correlation coefficients were r = -0.667, p < 0.0001 for RUL and r = -0.712, p < 0.0001 for LUL. In RUL and LUL groups, patients with a higher preoperative FEV(1.0)% of predicted had a more adverse percentage change in FEV(1.0) after surgery. In addition, all 13 patients with a preoperative FEV(1.0)% of predicted <60% in RUL and LUL groups had an increase in FEV(1.0) postoperatively. Patients with a lower preoperative FEV(1.0)% of predicted had a greater 'volume reduction effect' with an increase in FEV(1.0) after upper lobectomy. CONCLUSION: Upper lobectomy might have a volume reduction effect.

Aged↗

PubMed2026

Synovial short-lived plasma cells mediate adalimumab resistance in rheumatoid arthritis via MIF-CD74 axis-driven, partially TNF-α-independent inflammation.

OBJECTIVE: Synovial plasma cell infiltration predicts inadequate response to adalimumab in patients with rheumatoid arthritis (RA), yet the cellular and molecular mechanisms underlying this association remain unclear. This study aimed to dissect the functional heterogeneity of synovial plasma cells between adalimumab responders and non-responders at single-cell resolution, and to identify the molecular pathways driving treatment resistance. METHODS: This study was based on a prospective clinical cohort of 101 RA patients receiving adalimumab, from which synovial tissues of 8 patients (4 ACR20 responders and 4 non-responders) were profiled by 10x Genomics single-cell RNA sequencing (66,539 high-quality cells). A systematic ligand-receptor screening was performed to identify candidate signaling axes. Core findings were validated at four levels: an independent single-cell validation cohort (n = 4), external bulk RNA-seq cohorts (GSE15602, GSE47726), multiplex immunofluorescence on synovial tissues (n = 9 per group), and in vitro functional experiments using patient-derived peripheral blood monocyte-derived macrophages stimulated with recombinant human MIF under pharmacological intervention with adalimumab, the MIF inhibitor ISO-1, and an anti-CD74 neutralizing antibody. RESULTS: Plasma cells were significantly enriched in non-responder synovium, with a heterogeneous pattern characterized by quantitative accumulation of long-lived plasma cells (LLPCs) and functional dominance of short-lived plasma cells (SLPCs): SLPCs contributed 58.15% of total ribosomal module activity and preferentially overexpressed MIF. Systematic screening of 145 candidate ligand-receptor pairs identified MIF-CD74 as the only axis satisfying all four independent evidence layers. Tissue-level immunofluorescence confirmed that approximately 95% of synovial CD138+ plasma cells in non-responders co-expressed MIF, compared with approximately 45% in responders. In vitro, rh-MIF upregulated macrophage activation markers (CD74, CD80, CD86, HLA-DR) and induced IL-6 and TNF-α secretion. Adalimumab neutralized supernatant TNF-α but failed to suppress MIF-driven IL-6 and IL-1β activation, whereas ISO-1 and anti-CD74 effectively blocked MIF-induced effects at all levels examined. These findings were replicated in patient-derived PBMC macrophages. CONCLUSION: In adalimumab-resistant RA, a functionally active SLPC subset drives partially TNF-α-independent macrophage inflammation through the MIF-CD74 axis, representing a resistance pathway not fully addressed by anti-TNF therapy. Targeting MIF or CD74 blocked this axis in vitro, supporting MIF-CD74-directed precision intervention.

Adalimumab↗

PubMed1998

Muscle-specific splicing of a heterologous exon mediated by a single muscle-specific splicing enhancer from the cardiac troponin T gene.

The chicken cardiac troponin T (cTNT) gene contains a single 30-nucleotide alternative exon that is included in embryonic striated muscle and skipped in the adult. Transient-transfection analysis of cTNT minigenes in muscle and fibroblast cell cultures previously identified four muscle-specific splicing enhancers (MSEs) that promote exon inclusion specifically in embryonic striated muscle cultures. Three MSEs located in the intron downstream from the alternative exon were sufficient for muscle-specific exon inclusion. In the present study, the boundaries of these MSEs were defined by scanning mutagenesis, allowing analysis of individual elements in gain-of-function experiments. Concatamers of MSE2 were necessary and sufficient to promote muscle-specific inclusion of a heterologous exon, indicating that it is a target for muscle-specific regulation. Sequences present in MSE2 are also found in MSE4, suggesting that these two MSEs act in a similar manner. MSE3 appears to be different from MSE2 and MSE4 yet is able to functionally replace both of these elements, demonstrating functional redundancy of elements that are likely to bind different factors. MSE2 and MSE4 each contain a novel sequence motif that is found adjacent to a number of alternative exons that undergo regulated splicing in striated muscle, suggesting a common role for this element in muscle-specific regulation.

Animals↗

PubMed2003

Intrinsic signals regulate the initial steps of myogenesis in vertebrates.

In vertebrates, despite the evidence that extrinsic factors induce myogenesis in naive mesoderm, other experiments argue that the initiation of the myogenic program may take place independent of these factors. To resolve this discrepancy, we have re-addressed this issue, using short-term in vivo microsurgery and culture experiments in chick. Our results show that the initial expression of the muscle-specific markers Myf5 and MyoD is regulated in a mesoderm-autonomous fashion. The reception of a Wnt signal is required for MyoD, but not Myf5 expression; however, we show that the source of the Wnt signal is intrinsic to the mesoderm. Gain- and loss-of-function experiments indicate that Wnt5b, which is expressed in the presomitic mesoderm, represents the MyoD-activating cue. Despite Wnt5b expression in the presomitic mesoderm, MyoD is not expressed in this tissue: our experiments demonstrate that this is due to a Bmp inhibitory signal that prevents the premature expression of MyoD before somites form. Our results indicate that myogenesis is a multistep process which is initiated prior to somite formation in a mesoderm-autonomous fashion; as somites form, influences from adjacent tissues are likely to be required for maintenance and patterning of early muscles.

Animals↗

PubMed1979

Pharmacological studies on new oncostatic acridine derivatives. I. Acute and subchronic action.

Preclinical pharmacological studies of two acridine derivatives, dihydrochloride N10-oxide 1-nitro-9-/3-dimethylaminopropylamino/-acridine (C-666) and dihydrochloride 1-nitro-9-[(2-dimethylamino)-1-methylethylamino]-acridine (C-829) are reported. Both compounds are characterized by biological activity, poor absorption from the gastrointestinal tract and local irritant action. Quality differences in an effect of both investigated acridine derivatives on the central nervous system were noted. C-666 proved to be deprived of the effect typical of the central component compounds while C-829 demonstrated mostly sedative activity. Clear dissociation in the effect of these both compounds was seen in in vitro experiments on isolated smooth muscle organs. C-666 acted spasmolytically on the motory action of intestine muscles while C-829 acted spastically. Both preparations had clearly hipotensic influence which can be due to the vascular effect and to their affinity with the intramyocardium transmitting system. Neither a distinctive effect on reproductivity of animals nor the teratogenic action were observed in the functional experiments.

Acridines↗

PubMed2003

The role of Pitx2 during cardiac development. Linking left-right signaling and congenital heart diseases.

Pitx2 is a bicoid-related homeodomain transcription factor that plays a critical role in directing cardiac asymmetric morphogenesis. Ectopic Pitx2c expression in the developing myocardium correlates with double outlet right ventricle (DORV) in laterality mutants. Pitx2 loss of function experiments cause severe cardiovascular defects, such as atrial isomerism (AI), double inlet left ventricle, transposition of the great arteries (TGA), persistent truncus arteriosus (PTA), and abnormal aortic arch (AAA) remodeling. Current studies suggest that Pitx2-mediated signaling during cardiogenesis is conducted within three different cell types: the myocardium, the cardiac neural crest (CNC) cells, and the pharyngeal arch mesenchyme. Impaired Pitx2 function in discrete myocardial regions seems to lead to DORV, AI, and possibly TGA. On the other hand, impaired Pitx2 expression in the CNC leads preferentially to PTA. AAA remodeling is likely to occur owing to impaired cross-talk of the CNC cells with the pharyngeal arch mesenchyme. Thus, Pitx2 appears to be directing left-right identity to the cardiac venous components (e.g., the atria), whereas it appears to be modeling the morphologic arrangement of distinct myocardial components in the arterial pole. These data suggest that altered left-right signaling underlies the etiology of several common congenital cardiac malformations.

Animals↗

PubMed1998

Krüppel acts as a developmental switch gene that mediates Notch signalling-dependent tip cell differentiation in the excretory organs of Drosophila.

Cell proliferation in the excretory organs of Drosophila, the Malpighian tubules (MT), is under the control of a neural tip cell. This unique cell is singled out from equivalent MT primordial cells in response to Notch signalling. We show that the gene Krüppel (Kr), best known for its segmentation function in the early embryo, is under the control of the Notch-dependent signalling process. Lack-of-function and gain-of-function experiments demonstrate that Kr activity determines the neural fate of tip cells by acting as a direct downstream target of proneural basic helix-loop-helix (bHLH) proteins that are restricted in response to Notch signalling. We have identified a unique cis-acting element that mediates all spatial and temporal aspects of Kr gene expression during MT development. This element contains functional binding sites for the restricted proneural bHLH factors and Fork head protein which is expressed in all MT cells. Our results suggest a mechanism in which these transcription factors cooperate to set up a unique cell fate within an equivalence group of cells by restricting the activity of the developmental switch gene Kr in response to Notch signalling.

Animals↗