Twist2: role in corneal stromal keratocyte proliferation and corneal thickness.
OBJECTIVE
Twist2 is a member of a family of bHLH transcription factors critical for normal mesenchymal proliferation and differentiation. In this study, the authors analyzed the role of Twist2 in the eye and cornea through examination of a Twist2 loss-of-function mouse mutant.


METHODS
Twist2 expression during eye development in the mouse was investigated using RT-PCR and mRNA slide in situ hybridization. Lineage tracing was performed using Cre reporter mice. Morphometric analyses were performed, and cell proliferation and cell death were investigated by immunohistochemistry using Ki67 and cleaved caspase 3 antibodies, respectively.


RESULTS
In the mouse, Twist2 is expressed first in the periocular mesenchyme and subsequently in the corneal stroma and endothelium of the developing eye. Loss of Twist2 function leads to corneal thinning and a reduced population of stromal keratocytes. The reduction in the stromal cell population can be traced back to embryonic stages during which the proliferation of stromal progenitor cells is impaired and to the reduced number of proliferating cells in the corneal limbus postnatally. Adult Twist2-null mice display enophthalmia and blepharophimosis. Corneal thinning in mutant mice is not accompanied by glaucoma, an association reported in human patients.


CONCLUSIONS
Twist2 is required for normal corneal keratocyte proliferation and eyelid morphogenesis in the mouse. Loss of Twist2 function leads to corneal thinning because of the reduction in stromal keratocyte proliferation.
Weaving
Linda
L
Eye Genetics Research Group, Embryology, Children's Medical Research Institute, The Children's Hospital at Westmead, Save Sight Institute, Sydney, NSW, Australia.
Mihelec
Marija
M
Storen
Rebecca
R
Sosic
Drazen
D
Grigg
John R
JR
Tam
Patrick P L
PP
Jamieson
Robyn V
RV
D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis; D016569:Blepharophimosis / Q000235:genetics / Q000473:pathology; D053148:Caspase 3 / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology; D049109:Cell Proliferation; D003315:Cornea / Q000196:embryology* / Q000473:pathology*; D003319:Corneal Stroma / Q000196:embryology* / Q000378:metabolism; D015841:Enophthalmos / Q000235:genetics / Q000473:pathology; D005260:Female; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D005838:Genotype; D018257:Helix-Loop-Helix Motifs / Q000502:physiology; D017403:In Situ Hybridization; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009024:Morphogenesis; D012333:RNA, Messenger / Q000235:genetics; D012097:Repressor Proteins / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051879:Twist-Related Protein 1 / Q000502:physiology*
D012333:RNA, Messenger; D012097:Repressor Proteins; D051879:Twist-Related Protein 1; C096852:Twist2 protein, mouse; D053148:Caspase 3