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
P L
PL
Department of Anatomy, University of Iowa College of Medicine, Iowa City 52242.
Nanthakumar
E J
EJ
Snyder
J M
JM
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005314:Embryonic and Fetal Development / Q000502:physiology; D005865:Gestational Age; D006023:Glycoproteins / Q000378:metabolism; D006801:Humans; D008168:Lung / Q000196:embryology* / Q000378:metabolism; D008969:Molecular Sequence Data; D011663:Pulmonary Surfactants / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D011817:Rabbits; D051381:Rats; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity
D006023:Glycoproteins; D011663:Pulmonary Surfactants; D012333:RNA, Messenger