FREM1 deficiency causes lung lobulation defects in mice.

(A and A′) Ventral view of the lungs of a Frem1^eyes2/eyes2 mouse in which the right middle (RMd) and right caudal lobe (RCd) are fused with only small, partial fissures defining the boundaries of each lobe (yellow arrow). (B and B′) Dorsal view of the same lungs showing partial fusion of the right cranial lobe (RCr) to the fused right middle and caudal lobes (RMd/RCd) with an incomplete fissure separating these lobes (yellow arrow). In A′ and B′, the right lung lobes are outlined with a dashed yellow line. The left lung (L) and the right accessory lobe (RAc) are normal. H = heart.