Developmental regulation of surfactant-associated proteins in rabbit fetal lung in vivo
The developmental regulation of the rabbit surfactant-associated proteins, SP-A, SP-B, and SP-C, was investigated using Northern blot analysis. These proteins comprise approximately 10% by weight of pulmonary surfactant, a lipoprotein secreted by type II cells that reduces surface tension at the air-alveolar interface. SP-A mRNA and SP-B mRNA were first detected in rabbit fetal lung at day 24 of gestation (term = 31 days), i.e., approximately two days prior to the appearance of lamellar bodies within differentiated alveolar type II cells. The relative abundance of SP-B mRNA detected on day 24 of gestation was greater than that of SP-A mRNA. Fetal lung SP-A mRNA and SP-B mRNA levels increased rapidly during the remainder of gestation, reaching a maximum at day 31 of gestation. The relative concentrations of SP-A mRNA and SP-B mRNA were decreased in day 2 neonatal and adult lung tissues when compared to the levels present in fetal lung tissue late in gestation. A 0.5-kb rabbit SP-C cDNA was generated using the reverse transcriptase-polymerase chain reaction and was found to have high sequence homology to the human and rat SP-C cDNA nucleotide sequences. The predicted amino acid sequence for the rabbit SP-C cDNA revealed strong conservation of a hydrophobic region close to the amino terminus of the SP-C protein. Fetal lung SP-C mRNA was detected at day 19 of gestation, the earliest time point examined in this study. SP-C mRNA levels gradually increased in fetal lung tissue until day 28 of gestation and then remained level throughout the remainder of gestation and in the day 2 neonatal and adult rabbit lung tissue. These results suggest that the developmental pattern of induction of mRNA for the surfactant-associated proteins, SP-A, SP-B, and SP-C, differ from each other and are different in several respects from the developmental patterns observed in fetal lung tissue of the rat and human species.
Durham, Paul L., Elizabeth J. Nanthakumar, and Jeanne M. Snyder. "Developmental regulation of surfactant-associated proteins in rabbit fetal lung in vivo." Experimental lung research 18, no. 6 (1992): 775-793.
Experimental Lung Research