We have isolated and characterized murine surfactant protein (SP-B) cDNAs and determined both the cellular distribution and developmental expression of SP-B mRNA. The nucleotide sequence of the composite SP-B cDNAs and cloned genomic SP-B DNA predicted a primary translation product of 377 amino acids (molecular mass = 41.7 kDa) that contained a single asparagine linked glycosylation site. The 410 base 3' untranslated region contained a novel sequence consisting of a (CCA)21 repeat. Tissue specificity and developmental expression of SP-B mRNA was assessed by Northern blot analysis. A single 1.6-kb mRNA species was detected specifically in lung tissue. In fetal mouse lung SP-B mRNA was detected at low levels on day 15 of gestation and increased markedly between days 16 and 17, reaching adult levels by birth. In situ hybridization analysis of SP-B mRNA demonstrated SP-B expression primarily in bronchiolar and alveolar epithelium, although discrete bronchial cells also contained the SP-B mRNA. The murine SP-B mRNA was expressed in proximal and distal epithelial cells within the respiratory tract and shares a close structural relationship to SP-B from other species.

The murine beta-glucuronidase (GUS) gene complex, [Gus], encompasses the GUS structural element, Gus-s, and a set of regulatory elements which serve to modulate Gus-s expression. Three common GUS haplotypes representing virtually all inbred strains of laboratory mice have been compared with respect to GUS mRNA sequence. Results of such comparisons revealed sequence variations which target the location of one of the GUS regulatory elements to sequences within Gus-s and which account for known electrophoretic and heat stability differences among GUS allozymes of the three common GUS haplotypes.