Mouse A-type lamin genes were isolated. Structural analyses revealed that all the three known mouse A-type lamins (A, C and C2) were coded in a single genomic locus in a 22 kilobase DNA segment. The three lamins were coded in 12, 10 and 10 exons for A, C and C2, respectively, and shared 8 exons among them. Primer extension analyses identified possible transcription start sites for both A/C and C2 genes suggesting that the locus is under the control of two separate promoters, that is a somatic cell-acting promoter (for A and C) and a testis-specific promoter (for C2) which resides in the first intron of the A/C gene. Sequence characteristics of the possible promoter regions are discussed. Divergence of the two somatic cell-type lamins (A and C) is formally accounted for by differential selection of poly(A) sites together with lamin A-specific splicing.
