Increased activity of mesenchymal ALK2-BMP signaling causes posteriorly truncated microglossia and disorganization of lingual tissues

Epigenetic modifier G9a is involved in regulation of mouse tongue development

OBJECTIVES

The tongue comprises multiple tissues of different embryonic origins, including pharyngeal arch, somite, and cranial neural crest (CNC). However, its developmental regulatory mechanisms, especially those involving epigenetic modifiers, remain poorly understood. This study examined the roles of the epigenetic modifier G9a in murine tongue development.

METHODS

We deleted G9a using Sox 9 (SRY-related HMG-box gene 9)-Cre recombinase, which acts in tongue progenitor cells, including CNC-derived cells, to generate G9a conditional knockout (cKO) mice. Histochemical and immunohistochemical analyses were conducted on sections prepared from tongue tissues of control and cKO mice.

RESULTS

Cre-dependent LacZ reporter mice, generated by crossing Rosa-LacZ mice with sox9-Cre mice, revealed Cre recombinase activity in the mucosal epithelium and tongue connective tissue of the embryonic tongue. Tongue volume was significantly reduced on embryonic day 17.5 (E17.5) and postnatal day 0 (P0) in cKO mice. Histological sections showed that the lingual mucosal epithelium was thinner in cKO mice. Reduced G9a levels were accompanied by decreased levels of a G9a substrate, dimethylated lysine 9 in histone H3, in the embryonic tongue. BrdU injection at E16.5 revealed reduced numbers of BrdU-positive cells in the mucosal epithelium and underlying connective tissue at E17.5 in cKO mice, indicating suppression of cell proliferation in both tissues. Investigation of keratin 5 and 8 protein localization showed significantly suppressed expression in the lingual mucosal epithelium in cKO mice.

CONCLUSIONS

G9a is required for proper proliferation and differentiation of sox9-expressing tongue progenitor cells and is thereby involved in tongue development.

Taste papilla cell differentiation requires the regulation of secretory protein production by ALK3-BMP signaling in the tongue mesenchyme

Taste papillae are specialized organs, each of which comprises an epithelial wall hosting taste buds and a core of mesenchymal tissue. In the present study, we report that during early taste papilla development in mouse embryos, bone morphogenetic protein (BMP) signaling mediated by type 1 receptor ALK3 in the tongue mesenchyme is required for epithelial Wnt/β-catenin activity and taste papilla differentiation. Mesenchyme-specific knockout (cKO) of Alk3 using Wnt1-Cre and Sox10-Cre resulted in an absence of taste papillae at E12.0. Biochemical and cell differentiation analyses demonstrated that mesenchymal ALK3-BMP signaling governed the production of previously unappreciated secretory proteins, i.e. it suppressed those that inhibit and facilitated those that promote taste papilla differentiation. Bulk RNA-sequencing analysis revealed many more differentially expressed genes (DEGs) in the tongue epithelium than in the mesenchyme in Alk3 cKO versus control. Moreover, we detected downregulated epithelial Wnt/β-catenin signaling and found that taste papilla development in the Alk3 cKO was rescued by the GSK3β inhibitor LiCl, but not by Wnt3a. Our findings demonstrate for the first time the requirement of tongue mesenchyme in taste papilla cell differentiation.

Clinical manifestation score and characterization of cytokines and lymphocytes of dimethylacetamide-induced toxic hepatitis in spandex workers

Occupational exposure to dimethylacetamide (DMAc) has been reported to cause toxic hepatitis. Sixty spandex workers were included in this study to research the clinical manifestations and expression of cytokines and lymphocytes in DMAc-induced toxic hepatitis. Chinese drugs (reduced glutathione and Hugan tablets) were used to treat them. The manifestations including jaundice, asthenia, appetite, nausea, emesis, abdominal distension, yellow urine, and dizziness were scored. The percentages of patients rated as 0-3, 4-6, 7-9, and 10-12 points were 33.3%, 43.3%, 21.7%, and 1.7%, respectively, before treatment, and all patients showed 0-3 points after the treatment. The ultrasonic and CT imaging revealed diffuse intrahepatic hypodensity, intrahepatic calcification, signs of liver injury, and splenomegaly, which improved after therapy. Blood analysis showed that ALT, AST, TBIL, IL-6, IL-10, TNF-α, IFN-γ, CD3⁺%, and CD4⁺/CD8⁺ statistically decreased after drug treatment. Correlation analysis demonstrated positive linear correlations between ALT and TBIL, AST and TBIL, IL-10 and ATL, IL-10 and AST, IL-10 and TBIL, IFN-γ and IL-6, IFN-γ and TNF-α, and CD3⁺% and ALT. Pro-inflammatory cytokines and lymphocytes in DMAc-induced toxic hepatitis reflected an active immune state that decreased after treatment. IL-10 may inhibit the immune response in this disease, as a protective mechanism.

The sense of taste: Development, regeneration, and dysfunction

Gustation or the sense of taste is a primary sense, which functions as a gatekeeper for substances that enter the body. Animals, including humans, ingest foods that contain appetitive taste stimuli, including those that have sweet, moderately salty and umami (glutamate) components, and tend to avoid bitter-tasting items, as many bitter compounds are toxic. Taste is mediated by clusters of heterogeneous taste receptors cells (TRCs) organized as taste buds on the tongue, and these convey taste information from the oral cavity to higher order brain centers via the gustatory sensory neurons of the seventh and ninth cranial ganglia. One remarkable aspect of taste is that taste perception is mostly uninterrupted throughout life yet TRCs within buds are constantly renewed; every 1-2 months all taste cells have been steadily replaced. In the past decades we have learned a substantial amount about the cellular and molecular regulation of taste bud cell renewal, and how taste buds are initially established during embryogenesis. Here I review more recent findings pertaining to taste development and regeneration, as well as discuss potential mechanisms underlying taste dysfunction that often occurs with disease or its treatment. This article is categorized under: Infectious Diseases > Stem Cells and Development Cancer > Stem Cells and Development Neurological Diseases > Stem Cells and Development.

Deletion of Nf2 in neural crest-derived tongue mesenchyme alters tongue shape and size, Hippo signalling and cell proliferation in a region- and stage-specific manner

Objectives

The mammalian tongue develops from the branchial arches (1–4) and comprises highly organized tissues compartmentalized by mesenchyme/connective tissue that is largely derived from neural crest (NC). This study aimed to understand the roles of tumour suppressor Neurofibromin 2 (Nf2) in NC‐derived tongue mesenchyme in regulating Hippo signalling and cell proliferation for the proper development of tongue shape and size.

Materials and methods

Conditional knockout (cKO) of Nf2 in NC cell lineage was generated using Wnt1‐Cre (Wnt1‐Cre/Nf2^cKO). Nf2 expression, Hippo signalling activities, cell proliferation and tongue shape and size were thoroughly analysed in different tongue regions and tissue types of Wnt1‐Cre/Nf2^cKO and Cre^‐/Nf2^fx/fx littermates at various stages (E10.5–E18.5).

Results

In contrast to many other organs in which the Nf2/Hippo pathway activity restrains growth and cell proliferation and as a result, loss of Nf2 decreases Hippo pathway activity and promotes an enlarged organ development, here we report our observations of distinct, tongue region‐ and stage‐specific alterations of Hippo signalling activity and cell proliferation in Nf2^cKO in NC‐derived tongue mesenchyme. Compared to Cre⁻/Nf2^fx/fx littermates, Wnt1‐Cre/Nf2^cKO depicted a non‐proportionally enlarged tongue (macroglossia) at E12.5–E13.5 and microglossia at later stages (E15.5–E18.5). Specifically, at E12.5 Nf2^cKO mutants had a decreased level of Hippo signalling transcription factor Yes‐associated protein (Yap), Yap target genes and cell proliferation anteriorly, while having an increased Yap, Yap target genes and cell proliferation posteriorly, which lead to a tip‐pointed and posteriorly widened tongue. At E15.5, loss of Nf2 in the NC lineage resulted in distinct changes in cell proliferation in different regions, that is, high in epithelium and mesenchyme subjacent to the epithelium, and lower in deeper layers of the mesenchyme. At E18.5, cell proliferation was reduced throughout the Nf2^cKO tongue.