Tissue specific loss of A-type lamins in the gastrointestinal epithelium can enhance polyp size

The nuclear lamina, comprised of the A and B-type lamins, is important in maintaining nuclear shape and in regulating key nuclear functions such as chromatin organization and transcription. Deletion of the A-type lamins results in genome instability and many cancers show altered levels of A-type lamin expression. Loss of function mutations in the mouse Lmna gene result in early postnatal lethality, usually within 3-5 weeks of birth making an analysis of the role of lamins in carcinogenesis difficult. To circumvent early lethality, and determine the role of the A-type lamins in specific tissues in older mice we derived a conditional allele of Lmna^FL/FL (floxed). Lmna^FL/FL was specifically deleted in the gastrointestinal (GI) epithelium by crossing the Lmna^FL/FL mice with Villin-Cre mice. Mice lacking Lmna in the GI are overtly normal with no effects on overall growth, longevity or GI morphology. On a GI specific sensitized (Apc^Min/+) background, polyp numbers are unchanged, but polyp size is slightly increased, and only in the duodenum. Our findings reveal that although A-type lamins are dispensable in the postnatal GI epithelium, loss of Lmna under malignant conditions may, to a limited extent, enhance polyp size indicating that A-type lamins may regulate cell proliferation in the transformed GI epithelium.