The Iroquois homeobox gene, Irx5, is required for retinal cone bipolar cell development.
In the mouse retina, at least ten distinct types of bipolar interneurons are involved in the transmission of visual signals from photoreceptors to ganglion cells. How bipolar interneuron diversity is generated during retinal development is poorly understood. Here, we show that Irx5, a member of the Iroquois homeobox gene family, is expressed in developing bipolar cells starting at postnatal day 5 and is localized to a subset of cone bipolar cells in the mature mouse retina. In Irx5-deficient mice, defects were observed in the expression of some, but not all, immunohistological markers that define mature Type 2 and Type 3 OFF cone bipolar cells, indicating a role for Irx5 in bipolar cell differentiation. The differentiation of these two bipolar cell types has previously been shown to require the homeodomain-CVC transcription factor, Vsx1. However, the defects observed in Irx5-deficient retinas do not coincide with a reduction of Vsx1 expression, and conversely, the expression of Irx5 in cone bipolar cells does not require the presence of a functional Vsx1 allele. These results indicate that there are at least two distinct genetic pathways (Irx5-dependent and Vsx1-dependent) regulating the development of Type 2 and Type 3 cone bipolar cells.
Cheng
Chi Wa
CW
Program in Developmental Biology, The Hospital for Sick Children, and Department of Molecular and Medical Genetics, University of Toronto, Toronto, Ontario, Canada M5G 1X8.
Chow
Robert L
RL
Lebel
Mélanie
M
Sakuma
Rui
R
Cheung
Helen Oi-Lam
HO
Thanabalasingham
Vijitha
V
Zhang
Xiaoyun
X
Bruneau
Benoit G
BG
Birch
David G
DG
Hui
Chi-chung
CC
McInnes
Roderick R
RR
Cheng
Shuk Han
SH
D000818:Animals; D002454:Cell Differentiation / Q000235:genetics* / Q000502:physiology; D005136:Eye Proteins / Q000502:physiology; D005801:Genes, Homeobox / Q000502:physiology*; D018398:Homeodomain Proteins / Q000235:genetics / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D009457:Neuroglia / Q000502:physiology; D012160:Retina / Q000196:embryology*; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology* / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*
D005136:Eye Proteins; D018398:Homeodomain Proteins; C501601:Irx5 protein, mouse; D014157:Transcription Factors; C491582:Vsx1 protein, mouse