Biology subjects
Publications and source records attributed to Barlier, A..
Congenital melanocytic nevi (CMN) and common acquired melanocytic nevi (AMN) are melanoma-predisposing skin conditions presenting excessive numbers of melanocytes but arising at different times in life. Appropriately weighted whole-genome methylation analysis can be used as a basis for further research in dermatopathology and as applied here provides new insights into nevus biology.
RASopathies, rare congenital syndromes affecting multiple organ systems, often include peripheral neuropathy of unknown origin. While RASopathy-associated gene variants are proto-oncogenic, the impact of timing and mosaicism on pathogenicity remains poorly understood. Here, we investigate the links between Braf, a key mitogen-activated protein kinase (MAPK) effector, and peripheral neuropathy. By targeting Braf p.V600E, an oncogenic variant found in mosaic RASopathies, to embryonic Mpz-expressing cells in mice, we induced a congenital Charcot-Marie-Tooth-like degenerative neuropathy. This phenotype was characterized by hyperplastic nerves, hindlimb weakness, and unexpectedly reduced body size. Constitutively active Braf expanded a Jun+ Schwann cell repair state, impairing myelination and nerve homeostasis. To examine relevance to RASopathies, we differentiated patient-derived stem cells bearing the cardio-facio-cutaneous syndrome-associated BRAF p.Q257R variant into Schwann cells. Compared to wild-type controls, CFC-derived cells failed to acquire mature phenotypes, instead exhibiting progenitor or repair-type transcriptional profiles. Our findings implicate somatic mosaicism in the unresolved genetic heterogeneity of neuropathies and expand the candidate gene list for peripheral nerve disorders. Moreover, they reveal a MAPK-dependent mechanism linking neural crest-derived Schwann cell dysfunction to both body growth and nerve homeostasis, providing new insights into the mechanisms in RASopathy-associated neuropathy and potential therapeutic targets.
BackgroundDeficient Anterior pituitary with common Variable Immune Deficiency (DAVID) syndrome, combining adrenocorticotropic hormone deficiency (ACTHD) and primary hypogammaglobulinemia, is caused by NFKB2 heterozygous mutations. Nuclear factor kappa B (NFKB) signaling is a key regulator of the immune system; however, the underlying mechanism of its association with endocrine symptoms remains unknown. The role of NFKB2 in the development of the human pituitary was called into question by Nfkb2-deficient Lym1 mice, which have normal pituitary functions. PurposeThe aim of this study was to create a human disease model to define the role of NFKB2 in human pituitary development. MethodsWe established pituitary organoids in three-dimensional (3D) culture after directed differentiation from CRISPR/Cas9-edited human induced pluripotent stem cells (hiPSC). First, we conducted a proof-of-concept study, introducing a homozygous TBX19K146R/K146R missense pathogenic variant in hiPSC, an allele found in patients with congenital isolated ACTHD. We then used the same method to produce NFKB2D865G/D865G mutant organoids, harboring the pathogenic missense variant previously identified in DAVID patients. This mutation causes a failure of NFKB2 p100 phosphorylation that blocks processing to form active NFKB2 p52. We further characterized pituitary organoid development with bulk RNA sequencing and validated findings with quantitative RT-PCR and by immunofluorescence in section and whole organoids. ResultsAnalysis of wild-type (WT) organoids demonstrated that this in vitro model recapitulates corticotroph cell differentiation. TBX19K146R/K146R organoids conserved early expression of HESX1, but had significantly decreased PITX1, TBX19, LHX3, and POMC transcription. NFKB2D865G/D865G organoids also had dramatically reduced corticotrophs. Furthermore, NFKB2D865G/D865G significantly perturbs the expression of 67 genes known to contribute to pituitary development, among which 39 transcription factors. Differential expression was found for several growth factor genes or genes associated with the epithelial-to-mesenchymal transition and terminal endocrine differentiation. ConclusionWe used a combination of CRISPR/Cas9 editing and refinement of a 3D organoid culture protocol to model human ACTHD due to TBX19 or NFKB2 mutations. The NFKB2 variant studied induced a significant decrease in corticotroph differentiation, confirming the causative role of NFKB2 in isolated or syndromic ACTHD and demonstrating for the first time a direct functional role of NFKB2 in human pituitary development.
Recurrent missense mutations of the PIK3CA oncogene are among the most frequent drivers of human cancers. These often lead to constitutive activation of its product p110, a phosphatidylinositol 3-kinase (PI3K) catalytic subunit. In addition to causing a broad range of cancers, the H1047R mutation is also found in affected tissues of a distinct set of congenital tumors and malformations. Collectively termed PIK3CA-related disorders (PRDs), these lead to overgrowth of brain, adipose, connective and musculoskeletal tissues and/or blood and lymphatic vessel components. Vascular malformations are frequently observed in PRD, due to cell-autonomous activation of PI3K signaling within endothelial cells. These, like most muscle, connective tissue and bone, are derived from the embryonic mesoderm. However, important organ systems affected in PRDs are neuroectodermal derivatives. To further examine their development, we drove the most common post-zygotic activating mutation of Pik3ca in neural crest and related embryonic lineages. Outcomes included macrocephaly, cleft secondary palate and more subtle skull anomalies. Surprisingly, Pik3ca-mutant subpopulations of neural crest origin were also associated with widespread cephalic vascular anomalies. Mesectodermal neural crest is a major source of non-endothelial connective tissue in the head, but not the body. To examine the response of vascular connective tissues of the body to constitutive Pik3ca activity during development, we expressed the mutation by way of an Egr2 (Krox20) Cre driver. Lineage tracing led us to observe new lineages that had normally once expressed Krox20 and that may be co-opted in pathogenesis, including vascular pericytes and perimysial fibroblasts. Finally, Schwann cell precursors having transcribed either Krox20 or Sox10 and induced to express constitutively active PI3K were associated with vascular and other tumors. These murine phenotypes may aid discovery of new candidate human PRDs affecting craniofacial and vascular smooth muscle development as well as the reciprocal paracrine signaling mechanisms leading to tissue overgrowth.