Structural and functional characterization of the zebrafish lamin B receptor

The lamin B receptor (LBR) is an integral membrane protein of the inner nuclear membrane that is interacting with B-type lamins, chromatin and DNA. The complete loss of the protein in mouse mutants causes a reduced viability of embryos, and viable animals develop abnormalities of the skeleton. Here, we present the molecular characterization of the zebrafish LBR (zLBR) gene and the functional analysis of LBR during zebrafish embryogenesis. We found that the coding region of the LBR mRNA of zebrafish as well as of mammals is contained in 13 exons. At the protein level, human and zebrafish LBR exhibit a high sequence identity (57% and higher) in 8 of the 13 exons. Knockdown of zLBR by microinjection of 0.5-1.0 mM morpholino antisense oligonucleotides (MO) into 1- to 2-cell stage embryos reduced the amount of endogenous zLBR protein to approximately 10-20%. The viability of MO-injected embryos within 24 h was reduced to 70-77%. Surviving 1-day-old embryos exhibited morphological alterations including reduced growth of head structures, retardation of tail growth and a bent backbone and tail. Expression analysis of the transcription factors no tail (ntl) and goosecoid (gsc) by in situ hybridization suggests that these malformations are caused by altered cell migration during gastrulation. Our data indicate that the LBR of zebrafish and mammals are both required for correct development.