Biology subjects

Lehmann, O. J.

Publications and source records attributed to Lehmann, O. J..

4 recordsLinked to original sources

bioRxiv2025

Mechanistic insights into transcriptional regulation of ARHGAP36 expression identify a factor predictive of neuroblastoma survival

Cancer repeatedly exploits attributes fundamental for morphogenesis to advance malignancy and metastasis. This is illustrated by lineage specific transcription factors that regulate neural crest migration representing frequent drivers of malignancy. One such example is the forkhead transcription factor FOXC1 where gain of function is a feature of diverse cancers that is associated with an unfavourable prognosis. Using RNA-, ChIP-sequencing and CRISPR interference, we show that Foxc1 binds a locus in a region of closed chromatin to induce expression of Arhgap36, a tissue-specific inhibitor of Protein Kinase A. Because PKA is a core Hedgehog (Hh) pathway inhibitor, Foxc1s induction of Arhgap36 expression increases Hh activity. The function of Sufu, a PKA substrate and a second essential Hh pathway inhibitor, is likewise impaired. The resulting increased Hh pathway output is resistant to pharmacological inhibition of Smoothened, a phenotype of more aggressive cancers. The Foxc1-Arhgap36 relationship identified in murine cells was further evaluated in neuroblastoma, a neural crest derived pediatric malignancy. This demonstrated in a cohort of 1348 patients that high levels of ARHGAP36 are predictive of improved five-year survival. Accordingly, this study has identified as a novel transcription factor which enhances ARHGAP36 expression, one that induces Hh activity in multiple tissues during development. It also establishes a model by which increased levels of FOXC1 via ARHGAP36 and PKA inhibition dysregulate multiple facets of Hh signaling, and provides evidence demonstrating relevance to a common neural-crest derived malignancy.

molecular biology↗

bioRxiv2020

Pleiotropy in FOXC1-attributable phenotypes involves altered ciliation and cilia-dependent signaling

Alterations to cilia are responsible for a wide range of severe disease; however, understanding of the transcriptional control of ciliogenesis remains incomplete. We evaluated whether ciliary dysfunction contributed to the pleiotropic phenotypes caused by the Forkhead transcription factor FOXC1. Here, we show that patients with FOXC1-attributable Axenfeld-Rieger Syndrome (ARS) have a prevalence of ciliopathy-associated phenotypes comparable to syndromic ciliopathies. We demonstrate that altering the level of Foxc1, via shRNA mediated inhibition and mRNA overexpression, modifies cilia length in vitro. These structural changes were associated with substantially perturbed cilia-dependent signaling [Hedgehog (Hh) and PDGFR] and the altered ciliary compartmentalization of a major Hh pathway transcription factor, Gli2. Analyses of two Foxc1 murine mutant strains demonstrated altered axonemal length in the choroid plexus with the increased expression of an essential regulator of multi-ciliation, Foxj1. The novel complexity revealed in ciliation of the choroid plexus indicates a partitioning of function between these Forkhead transcription factors. Collectively, these results support a contribution from ciliary dysfunction to some FOXC1-induced phenotypes.

genetics↗

bioRxiv2020

The Axenfeld-Rieger syndrome gene FOXC1 contributes to left-right patterning

Normal body situs requires precise spatiotemporal expression of the Nodal-Lefty-Pitx2 cascade in the lateral plate mesoderm. The ultimate output of this patterning is establishment of the left-right axis, which provides vital cues for correct organ formation and function. Mutations, deletions and duplications in PITX2 and FOXC1 lead to the rare genetic disease Axenfeld-Rieger syndrome (ARS). While situs defects are not a recognised feature of ARS, partial penetrance of cardiac septal defects and valve incompetence is observed; both of these congenital heart defects (CHDs) also occur following disruption of left-right patterning. Here we investigated whether foxc1 genes have a critical role in specifying organ situs. We demonstrate that CRISPR/Cas9 generated mutants for the zebrafish paralogs foxc1a and foxc1b recapitulate ARS phenotypes including craniofacial dysmorphism, hydrocephalus and intracranial haemorrhage. Furthermore, foxc1a-/-; foxc1b-/- mutant animals display cardiac and gut situs defects. Modelling FOXC1 duplication by transient mRNA overexpression revealed that increased foxc1 dosage also results in organ situs defects. Analysis of known left-right patterning genes revealed a loss in expression of the NODAL antagonist lefty2 in the lateral plate mesoderm. Consistently, LEFTY2 mutations are known to cause human cardiac situs defects. Our data reveal a novel role for the forkhead-box transcription factor foxc1 in patterning of the left-right axis, and provide a plausible mechanism for the incidence of congenital heart defects in Axenfeld-Rieger syndrome patients. Author SummaryThis manuscript investigates the functional consequences of abrogating the activity of Foxc1 (Forkhead Box C1). We demonstrate that loss of zebrafish foxc1a and foxc1b results in phenotypes that resemble human patients with deletions in the FOXC1 locus. Notably, such phenotypes include alterations to the morphology of the heart. Investigations into the mechanisms underlying this phenotype led to the discovery that Foxc1 functions as a regulator of left-right patterning. Most components of left-right specification function normally in foxc1a/b mutants, but there is a pronounced loss of lefty2, a known inhibitor of Nodal signaling. This supports a model in which Foxc1 regulates situs of the heart via the regulation of Lefty2.

genetics↗

bioRxiv2018

Morphogenesis and differentiation of embryonic vascular smooth muscle cells in zebrafish

Despite the critical role of vascular mural cells (smooth muscle cells and pericytes) in supporting the endothelium of blood vessels, we know little of their early morphogenesis and differentiation. foxc1b:EGFP expressing cells in zebrafish associate with the vascular endothelium (kdrl) and co-express a smooth muscle marker (acta2), but not a pericyte marker (pdgfr{beta}). The expression of foxc1b in early peri-endothelial mesenchymal cells allows us to follow the morphogenesis of mesenchyme into acta2 expressing vascular smooth muscle cells. We show that mural cells expressing different markers associate with vessels of different diameters, depending on their embryonic location and developmental timing, suggesting marker expression is predictive of functional differences. We identify gene expression signatures for an enriched vascular smooth muscle cell population (foxc1b + acta2) and all smooth muscle (acta2) using fluorescence-activated cell sorting and RNA-Seq. Finally, we demonstrate that progressive loss of foxc1a/foxc1b results in decreased smooth muscle cell coverage. Together, our data highlight the early cellular dynamics and transcriptome profiles of smooth muscle cells in vivo, using foxc1b as a unique tool to probe vascular smooth muscle cell differentiation.\n\nSummary StatementTracing the morphogenesis and transcriptome of early vascular smooth muscle cells using foxc1b

developmental biology↗