Distinct expression pattern of insulin-like growth factor family in rodent taste buds.
The insulin-like growth factor (IGF) system is an important regulator of growth and differentiation in a variety of tissues. In the present study, the expression of IGF family members in the taste buds of mice and rats was examined. By reverse transcriptase polymerase chain reaction (RT-PCR) analysis, mRNA of IGF-I and -II, IGF-I receptor (IGF-IR), insulin receptor (insulin R), and IGF-binding protein (IGFBP)-2, -3, -4, -5, and -6 was detected in the taste bud-containing epithelium of the circumvallate papillae of mice. As suggested by the study using degenerate PCR (McLaughlin [2000] J. Neurosci. 20:5679-5688), IGF-IR was expressed in most of the taste bud cells of adult mice, as found by immunohistochemistry, and in those of postnatal day (P) 6 mice by in situ hybridization. Insulin R, which has strong homology to IGF-IR, was also detected in most of the taste bud cells of mice by immunohistochemistry and in situ hybridization. IGF-I immunoreactivity was detected in a few taste bud cells and in the epithelium surrounding taste buds. Northern blot analysis revealed that the amount of IGF-I mRNA in taste bud-containing epithelium was very low compared with that in liver. IGF-II immunoreactivity was weakly detected in mouse taste buds and the surrounding epithelium. In the rat tissue, a subset of the taste bud cells was positive for IGF-II. Among the six IGFBPs, IGFBP-2, -5, and -6 were detected in the mouse taste buds: IGFBP-2 and -5 immunoreactivity was seen in the majority of the taste bud cells, whereas IGFBP-6 immunoreactivity was found in the nerve fibers innervating the taste buds. In situ hybridization study also revealed that IGFBP-2 and -5 mRNA was synthesized in the taste buds of P6 mice and that the expression of these mRNAs overlapped in von Ebner's glands. These data reveal that IGF-I and -II might be produced in taste bud cells and (or) surrounding lingual epithelium and act through IGF-IR and insulin R locally in a paracrine and autocrine manner. The activity of these IGFs may be modulated through their interaction with IGFBP-2, -5, and 6.
Suzuki
Yuko
Y
Department of Oral Anatomy, School of Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu 061-0293, Japan. suzuki@hoku-iryo-u.ac.jpb
Takeda
Masako
M
Sakakura
Yasunori
Y
Suzuki
Noriyo
N
D000367:Age Factors; D000818:Animals; D005260:Female; D051379:Mice; D009475:Neurons, Afferent / Q000378:metabolism*; D011247:Pregnancy; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D017451:Receptors, Somatomedin / Q000235:genetics / Q000378:metabolism*; D013002:Somatomedins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D013045:Species Specificity; D013650:Taste Buds / Q000166:cytology / Q000378:metabolism*; D014018:Tissue Distribution
D012333:RNA, Messenger; D017451:Receptors, Somatomedin; D013002:Somatomedins