Differential expression of a BMP4 reporter allele in anterior fungiform versus posterior circumvallate taste buds of mice

Abstract

BackgroundBone Morphogenetic Protein 4 (BMP4) is a diffusible factor which regulates embryonic taste organ development. However, the role of BMP4 in taste buds of adult mice is unknown. We utilized transgenic mice with LacZ under the control of the BMP4 promoter to reveal the expression of BMP4 in the tongues of adult mice. Further we evaluate the pattern of BMP4 expression with that of markers of specific taste bud cell types and cell proliferation to define and compare the cell populations expressing BMP4 in anterior (fungiform papillae) and posterior (circumvallate papilla) tongue.ResultsBMP4 is expressed in adult fungiform and circumvallate papillae, i.e., lingual structures composed of non-taste epithelium and taste buds. Unexpectedly, we find both differences and similarities with respect to expression of BMP4-driven ß-galactosidase. In circumvallate papillae, many fusiform cells within taste buds are BMP4-ß-gal positive. Further, a low percentage of BMP4-expressing cells within circumvallate taste buds is immunopositive for markers of each of the three differentiated taste cell types (I, II and III). BMP4-positive intragemmal cells also expressed a putative marker of immature taste cells, Sox2, and consistent with this finding, intragemmal cells expressed BMP4-ß-gal within 24 hours after their final mitosis, as determined by BrdU birthdating. By contrast, in fungiform papillae, BMP4-ß-gal positive cells are never encountered within taste buds. However, in both circumvallate and fungiform papillae, BMP4-ß-gal expressing cells are located in the perigemmal region, comprising basal and edge epithelial cells adjacent to taste buds proper. This region houses the proliferative cell population that gives rise to adult taste cells. However, perigemmal BMP4-ß-gal cells appear mitotically silent in both fungiform and circumvallate taste papillae, as we do not find evidence of their active proliferation using cell cycle immunomarkers and BrdU birthdating.ConclusionOur data suggest that intragemmal BMP4-ß-gal cells in circumvallate papillae are immature taste cells which eventually differentiate into each of the 3 taste cell types, whereas perigemmal BMP4-ß-gal cells in both circumvallate and fungiform papillae may be slow cycling stem cells, or belong to the stem cell niche to regulate taste cell renewal from the proliferative cell population.

Induction of ectopic taste buds by SHH reveals the competency and plasticity of adult lingual epithelium

“…Our expression analysis is not an exhaustive survey of regulatory genes expressed in adult taste buds, which include members of the Notch, TGFβ and Wnt pathways (Gaillard and Barlow, 2011;Nakamura et al, 2010;Nguyen and Barlow, 2010;Seta et al, 2003), as well as numerous transcription factor genes, such as Six1, Six4, Ascl1, Hes6 and Hes1 (Ota et al, 2009;Seta et al, 2003Seta et al, , 2011Suzuki et al, 2010). The degree to which these genes are similarly or differentially expressed by endogenous versus ectopic taste buds might shed light on the genes that are required for taste cell differentiation regardless of location versus those required for interactions with sensory afferents or perhaps for taste papilla genesis.…”

“…Immunofluorescence was performed on 12 µm cryosections as described (Nguyen and Barlow, 2010). Primary antisera and dilutions: rat anti-K8 (Troma) (1:200; Developmental Studies Hybridoma Bank, University of Iowa, USA), rabbit anti-claudin 4 (1:250; 364800, Invitrogen), rabbit antiNTPDase2 (1:3000; mN2-36L, CHUQ), rabbit anti-α-gustducin (1:1000; sc-395, Santa Cruz), rabbit anti-SNAP25 (1:8000; S9684, Sigma), rabbit anti-PLCβ2 (1:1000; sc-206, Santa Cruz), rabbit anti-NCAM (1:1000; AB5032, Millipore), goat anti-KCNQ1 (1:500; sc-10646, Santa Cruz), guinea pig anti-TRPM5 (1:1000; from Dr Emily Liman at USC), goat anti-CAR4 (1:1000; AF2414, R&D Systems), rabbit anti-K14 (1:3500; PRB-155P, Covance), guinea pig anti-K13 (1:500; BP5076, Acris Antibodies), goat anti-SOX2 (1:500; sc-17320, Santa Cruz), rabbit anti-SKN-1A (POU2F3) (1:500; sc-330, Santa Cruz), rabbit anti-P2X2 (1:500; APR-003, Alomone Labs), rabbit anti-PGP9.5 (1:1000; 7863-0504, AbD Serotec), rabbit anti-β-galactosidase (1:1000; 55976, MP Biomedicals) and chicken anti-GFP (1:1000; GFP-1020, Aves Labs).…”

Progress and renewal in gustation: new insights into taste bud development

“…Taste cells are continually renewed in adults, with an average taste cell lifespan of 10-14 days in rodents (Beidler and Smallman, 1965;Farbman, 1980 constantly replaced by new cells that enter the taste buds and complete differentiation within 2-3 days of their final division (Cho et al, 1998;Hamamichi et al, 2006;Miura et al, 2006;Nguyen and Barlow, 2010;Perea-Martinez et al, 2013). If taste cells are homogeneous in terms of lifespan, one can estimate that 10% of cells are lost each day via natural attrition, ∼20-30% of the cells are new and undergoing differentiation, and the remaining 60-70% are functional taste cells.…”

“…Interestingly, during embryogenesis BMP signaling promotes taste fate during placode specification and then represses taste fate once taste placodes have formed (Zhou et al, 2006). Bmp4 is also expressed in and around adult taste buds (Nguyen and Barlow, 2010), but it is not known if or how BMP signaling affects taste cell turnover, nor how this pathway interacts with Hh and Wnt/β-catenin.…”

Developing and Regenerating a Sense of Taste

“…In adults, SHH-receiving cells in the mesenchyme have been proposed to comprise a niche for taste bud cell maintenance (Liu et al, 2013), an idea that was suggested initially based on expression of Bmp4 in the taste papilla mesenchyme (Nguyen and Barlow, 2010). Likewise, in the embryonic tongue, in addition to signaling to adjacent epithelium, Shh + taste placodes signal to the subjacent mesenchymal compartment.…”