Mitotic activity and specification of fibrocyte subtypes in the developing rat cochlear lateral wall.
Spiral ligament fibrocytes (SLFs) in the mammalian cochlear lateral wall participate in K(+) recycling; they are classified into five subtypes based on their morphology, distribution, and function. Regeneration of SLFs is a potential therapeutic strategy for correcting several types of hearing loss, prompting us to investigate how SLF subtypes are established during development. We compared transitional SLF-type marker expression with mitotic activity to evaluate proliferation-differentiation relationships in SLFs from postnatal rat cochleae. I.p. injection of 5-bromo-2'-deoxyuridine (BrdU) demonstrated that the overall mitotic activity of SLFs decreased significantly between postnatal day 7 (P7) and P10. For all developmental periods, BrdU incorporation was weakest in the area where type I SLFs reside. The onset of expression of markers for type II/IV SLFs followed the reduced mitotic activity of the cells, whereas that of aquaporin-1, a marker for type III SLFs, was already detectable at P7, when the type III SLFs were still proliferating vigorously. Distribution of BrdU(+) cells increased in the area of type I SLFs between P7 and P10, suggesting migration of SLFs from adjacent areas. We conclude that the time course of development of SLFs is subtype-specific.
Mutai
H
H
Laboratory of Auditory Disorders, National Institute of Sensory Organs, National Tokyo Medical Center, 2-5-1 Higashigaoka, Meguro, Tokyo, Japan.
Nagashima
R
R
Fujii
M
M
Matsunaga
T
T
D000818:Animals; D000831:Animals, Newborn; D051398:Aquaporin 1 / Q000378:metabolism; D001973:Bromodeoxyuridine; D002454:Cell Differentiation / Q000502:physiology; D049109:Cell Proliferation; D003051:Cochlea / Q000254:growth & development* / Q000502:physiology*; D005347:Fibroblasts / Q000502:physiology*; D006309:Hearing; D007150:Immunohistochemistry; D008938:Mitosis / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
C496022:Aqp1 protein, rat; D051398:Aquaporin 1; D001973:Bromodeoxyuridine