Abstract
The cAMP response element binding protein 1 (Creb1) transcription factor regulates cellular gene expression in response to elevated levels of intracellular cAMP. Creb1 −/− fetal mice are phenotypically smaller than wildtype littermates, predominantly die in utero and do not survive after birth due to respiratory failure. We have further investigated the respiratory defect of Creb1−/− fetal mice during development. Lungs of Creb1−/− fetal mice were pale in colour and smaller than wildtype controls in proportion to their reduced body size. Creb1−/− lungs also did not mature morphologically beyond E16.5 with little or no expansion of airway luminal spaces, a phenotype also observed with the Creb1−/− lung on a Crem −/− genetic background. Creb1 was highly expressed throughout the lung at all stages examined, however activation of Creb1 was detected primarily in distal lung epithelium. Cell differentiation of E17.5 Creb1 −/− lung distal epithelium was analysed by electron microscopy and showed markedly reduced numbers of type-I and type-II alveolar epithelial cells. Furthermore, immunomarkers for specific lineages of proximal epithelium including ciliated, non-ciliated (Clara), and neuroendocrine cells showed delayed onset of expression in the Creb1−/− lung. Finally, gene expression analyses of the E17.5 Creb1 −/− lung using whole genome microarray and qPCR collectively identified respiratory marker gene profiles and provide potential novel Creb1-regulated genes. Together, these results demonstrate a crucial role for Creb1 activity for the development and differentiation of the conducting and distal lung epithelium.
Highlights
Survival at birth is critically dependent upon the ability of the lung to immediately take over the role of gas exchange, which in turn, is dependent upon the development of a mature respiratory system during the fetal period
In this report we have investigated the role of cAMP response element binding protein 1 (Creb1) (cyclic adenosine 39,59-monophosphate response element binding protein), a downstream transcriptional mediator for a range of systemic signalling factors, in respiratory epithelial differentiation
Investigation of the top ten most differentially expressed targets in the microarray list (Table 1) identified a number of genes known or suspected to be over- or underexpressed in the lungs of Creb12/2 fetal mice. These included: Surfactant associated protein D (Sftpd), which we found under-expressed in the lung of E17.5 Creb12/2 mice as previously described (Fig. 5D and Fig. 7), Scgb1a1, which we found did not show evidence of protein expression until E18.5 in the Creb12/2 lung (Fig. 8), and cAMP response element modulatory protein (Crem), which we found over-expressed in the lung of E17.5 Creb12/2 mice (Fig. 2A)
Summary
Survival at birth is critically dependent upon the ability of the lung to immediately take over the role of gas exchange, which in turn, is dependent upon the development of a mature respiratory system during the fetal period. Neuroepithelial, ciliated, and non-ciliated secretory Clara cells differentiate within the airway buds that undergo branching morphogenesis during the pseudoglandular stage (,E10.5–E16.5), while more-distally located alveolar epithelial cells (AECs) begin to differentiate later during the canalicular stage (E16.5–E17.5). Correct differentiation into these cell types, those populating the distal epithelium, is essential to ensure sufficient levels of pulmonary surfactant and surface area for gas exchange, which together are required for survival at birth. In this report we have investigated the role of Creb (cyclic adenosine 39,59-monophosphate (cAMP) response element binding protein), a downstream transcriptional mediator for a range of systemic signalling factors, in respiratory epithelial differentiation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
