Figure 5.

(a) RT-PCR and immunoblot demonstrate the presence of SRFΔ5 in fresh (uncultured) mouse undifferentiated peribronchial mesenchymal cells on day 11 (E11) and absence of SRFΔ5 with concomitant increment in SRF on day 14 (E14), after the peribronchial cells become SM cells. S18 represents an internal control. The increment in SRF isoforms was best seen at the protein rather than at the message level. (b) RT-PCR shows SRF and SRFΔ5 mRNA changes along with cell spread–induced SM differentiation in culture. Notice the increment in SRF mRNA and the decrease and disappearance of SRFΔ5 mRNA. (c) RT-PCR demonstrates rapid disappearance of SRFΔ5 mRNA and increments in SRF mRNA upon 4 hours of sustained stretch. The same change is seen at the protein level after 12 hours in the immunoblot in the lower panel. (d) Effect of peribronchial mesenchymal cell stretch on SRF and SRFΔ5 isoforms in lung organ cultures. One percent dextran inside the airways led to suppression of SRFΔ5 and increase in SRF (lane 2), whereas dextran in the medium outside the lung explants maintained the SRF isoform profile characteristic of undifferentiated mesenchymal cells (lane 3). (e and f) Effect of cell spreading (e) and stretching (f) on SRFΔ5 in human fetal mesenchymal cells. Notice that the very low levels of SRFΔ5 mRNA found in the human cells are likely a reflection of their more advanced stage of SM differentiation. Results shown are representative of three experiments, each done on duplicate samples per treatment.