Spliced isoforms of LIM‐domain‐binding protein (CLIM/NLI/Ldb) lacking LIM interaction domain

Abstract

LIM-domain-binding proteins (CLIM/NLI/Ldb) are involved in a variety of developmental processes by assembling into functional complexes with the LIM homeodomain transcription factors (LIM-HD) and LIM-only proteins (LMO) through the LIM-interaction domain (LID). The LID of Ldb is located in the carboxy-terminal region, and encoded by the last exon (exon 11) of Ldb genes. It has been known that the mammalian CLIM1/Ldb2 gene has a splice isoform, named CLIM1b, lacking LID. Little is known about the nature of CLIM1b, and this type of alternative splicing is very well conserved among mammals and chicken but not in Xenopus and teleost fish. Here, we demonstrate that other Ldb genes also have splice isoforms lacking LID: Ldb4b in teleost fish; and Ldb1b in tetrapods (mammals, chicken, and Xenopus). All these alternative splicing occur in intron 10 and exon 11, but the splicing patterns are different among the isoforms. The nature of zebrafish Ldb4b is examined by expression of the protein in E. coli and mammalian culture cells. Ldb4b localized in the nucleus when expressed in mammalian culture cells. Ldb4b did not bind Lhx3 directly. However, Ldb4b bound Ldb4a, the splice isoform of Ldb4 containing LID, and LMO4 via Ldb4a. These findings suggest that splice isoforms of Ldb lacking LID are potential regulator of Ldb function. This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan.