XMAN1, an inner nuclear membrane protein, antagonizes BMP signaling by interacting with Smad1 inXenopusembryos

Abstract

A family of inner nuclear membrane proteins is implicated in gene regulation by interacting with chromatin, nuclear lamina and intranuclear proteins; however, the physiological functions of these proteins are largely unknown. Using a Xenopus expression screening approach with an anterior neuroectoderm cDNA library, we have identified an inner nuclear membrane protein, XMAN1, as a novel neuralizing factor that is encoded by theXenopus ortholog of human MAN1. XMAN1 mRNA is expressed maternally, and appears to be restricted to the entire ectoderm at the early gastrula stage, then to the anterior neuroectoderm at the neurula stage. XMAN1 induces anterior neural markers without mesoderm induction in ectodermal explants, and a partial secondary axis when expressed ventrally by dorsalizing the ventral mesoderm. Importantly, XMAN1 antagonizes bone morphogenetic protein (BMP) signaling downstream of its receptor Alk3, as judged by animal cap assays, in which XMAN1 blocks expression of downstream targets of BMP signaling (Xhox3 and Msx1), and by luciferase reporter assays, in which XMAN1 suppresses BMP-dependent activation of theXvent2 promoter. Deletion mutant analyses reveal that the neuralizing and BMP-antagonizing activities of XMAN1 reside in the C-terminal region, and that the C-terminal region binds to Smad1, Smad5 and Smad8, which are intracellular mediators of the BMP pathway. Interference with endogenous XMAN1 functions with antisense morpholino oligos leads to the reduction of anterior neuroectoderm. These results provide the first evidence that the nuclear envelope protein XMAN1 acts as a Smad-interacting protein to antagonize BMP signaling during Xenopus embryogenesis.

Mouse neutrophils lacking lamin B-receptor expression exhibit aberrant development and lack critical functional responses

“…One possibility is that loss of LBR expression directly affects the activities of a transcription factor that regulates gp91 phox gene expression. Several recent studies of other inner nuclear envelope proteins lend support to this notion; the Xenopus homolog of mammalian MAN1, XMAN1, was shown to block transcriptional regulation by bone morphogenetic protein, and LAP2β repressed the transcriptional activity of several transcription factors, including E2F family members p53 and NF-kB [38][39][40]. Multiple transcriptional regulators have been identified to positively regulate gp91 phox expression, including NF-kB, PU.1, C/EBPε and HoxA9 [41][42][43][44].…”

Direct Binding of Nuclear Membrane Protein MAN1 to Emerin in Vitro and Two Modes of Binding to Barrier-to-Autointegration Factor

“…In Xenopus embryos, the proposed MAN1 alleles named XMAN1 and SANE (Smad1 antagonistic effector) regulate dorsal-ventral axis determination (3,11,12). The C-terminal domain of XMAN1 antagonizes signaling by bone morphogenetic proteins by binding directly to Smad1, Smad5, or Smad8, which are downstream effectors of signal transduction pathways triggered when BMP-4 binds its receptor at the plasma membrane (3).…”

Inner nuclear membrane and signal transduction

“…Osada et al [2003] further demonstrated that the Xenopus MAN1 orthologue antagonized BMP signaling downstream of its receptor in animal cap development and BMP reporter gene activation assays. They also showed that the ectoderm neutralizing and BMP-antagonizing activities of MAN1 resided in the carboxyl-terminal region and that this region bound to Smad1, Smad5, and Smad8.…”

“…MAN1 was also identified as a Smad1 binding protein that antagonizes BMP signaling in a functional screen for cDNAs that neutralized ectoderm formation in Xenopus development [Osada et al, 2003]. Osada et al [2003] further demonstrated that the Xenopus MAN1 orthologue antagonized BMP signaling downstream of its receptor in animal cap development and BMP reporter gene activation assays.…”