Six1 is essential for early neurogenesis in the development of olfactory epithelium.
The olfactory epithelium (OE) is derived from the olfactory placode (OP) during mouse development. At embryonic day (E) 10.0-E10.5, "early neurogenesis" occurs in the OE, which includes production of pioneer neurons that emigrate out of the OE and other early-differentiated neurons. Around E12.5, the OE becomes organized into mature pseudostratified epithelium and shows "established neurogenesis," in which olfactory receptor neurons (ORNs) are differentiated from basal progenitors. Little is known about the molecular pathway of early neurogenesis. The homeodomain protein Six1 is expressed in all OP cells and neurogenic precursors in the OE. Here we show that early neurogenesis is severely disturbed despite the unaltered expression of Mash1 at E10.5 in the Six1-deficient mice (Six1-/-). Expression levels of neurogenin1 (Ngn1) and NeuroD are reduced and those of Hes1 and Hes5 are augmented in the OE of Six1-/- at E10.5. Pioneer neurons and cellular aggregates, which are derived from the OP/OE and situated in the mesenchyme between the OE and forebrain, are completely absent in Six1-/-. Moreover, ORN axons and the gonadotropin-releasing hormone-positive neurons fail to extend and migrate to the forebrain, respectively. Our study indicates that Six1 plays critical roles in early neurogenesis by regulating Ngn1, NeuroD, Hes1, and Hes5.
Ikeda
Keiko
K
Division of Biology, Center for Molecular Medicine, Jichi Medical University, Shimotsuke, Tochigi 329-0498, Japan.
Ookawara
Shigeo
S
Sato
Shigeru
S
Ando
Zen-ichi
Z
Kageyama
Ryoichiro
R
Kawakami
Kiyoshi
K
D000818:Animals; D002454:Cell Differentiation; D003433:Crosses, Genetic; D004622:Embryo, Mammalian / Q000378:metabolism*; D004848:Epithelium / Q000196:embryology; D005260:Female; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D018034:Olfactory Receptor Neurons / Q000196:embryology*
D018398:Homeodomain Proteins; C490947:Six1 protein, mouse