Unique spatial and cellular expression patterns of Hoxa5, Hoxb4, and Hoxb6 proteins in normal developing murine lung are modified in pulmonary hypoplasia.
BACKGROUND
Hox transcription factors modulate signaling pathways controlling organ morphogenesis and maintain cell fate and differentiation in adults. Retinoid signaling, key in regulating Hox expression, is altered in pulmonary hypoplasia. Information on pattern-specific expression of Hox proteins in normal lung development and in pulmonary hypoplasia is minimal. Our objective was to determine how pulmonary hypoplasia alters temporal, spatial, and cellular expression of Hoxa5, Hoxb4, and Hoxb6 proteins compared to normal lung development.


METHODS
Temporal, spatial, and cellular Hoxa5, Hoxb4, and Hoxb6 expression was studied in normal (untreated) and nitrofen-induced hypoplastic (NT-PH) lungs from gestational day 13.5, 16, and 19 fetuses and neonates using Western blot and immunohistochemistry.


RESULTS
Modification of protein levels and spatial and cellular Hox expression patterns in NT-PH lungs was consistent with delayed lung development. Distinct protein isoforms were detected for each Hox protein. Expression levels of the Hoxa5 and Hoxb6 protein isoforms changed with development and were altered further in NT-PH lungs. Compared to normal lungs, GD19 and neonatal NT-PH lungs had decreased Hoxb6 and increased Hoxa5 and Hoxb4. Hoxa5 cellular localization changed from mesenchyme to epithelia earlier in normal lungs. Hoxb4 was expressed in mesenchyme and epithelial cells throughout development. Hoxb6 remained mainly in mesenchymal cells around distal airways.


CONCLUSIONS
Unique spatial and cellular expression of Hoxa5, Hoxb4, and Hoxb6 participates in branching morphogenesis and terminal sac formation. Altered Hox protein temporal and cellular balance of expression either contributes to pulmonary hypoplasia or functions as a compensatory mechanism attempting to correct abnormal lung development and maturation in this condition.
Div. of Newborn Medicine, Department of Pediatrics, Tufts Medical Center, Boston, Massachusetts 02111, USA. mvolpe1@tuftsmedicalcenter.org
MaryAnn Vitoria
MV
Volpe
Karen Ting Wai
KT
Wang
Heber Carl
HC
Nielsen
Mala Romeshchandra
MR
Chinoy
D000818:Animals; D000831:Animals, Newborn; D005260:Female; D018398:Homeodomain Proteins / Q000378:metabolism*; D008168:Lung / Q000002:abnormalities* / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D008171:Lung Diseases / Q000139:chemically induced / Q000151:congenital / Q000378:metabolism; D051379:Mice; D010647:Phenyl Ethers; D010750:Phosphoproteins / Q000378:metabolism*; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000139:chemically induced / Q000378:metabolism; D014018:Tissue Distribution / Q000187:drug effects; D014157:Transcription Factors / Q000378:metabolism*
D018398:Homeodomain Proteins; C059637:Hoxa5 protein, mouse; C513262:Hoxb4 protein, mouse; C490537:Hoxb6 protein, mouse; D010647:Phenyl Ethers; D010750:Phosphoproteins; D014157:Transcription Factors; C007350:nitrofen