title: A Conditional Knockout Mouse Model Reveals That Calponin-3 Is Dispensable for Early B Cell Development.
abstract: Calponins form an evolutionary highly conserved family of actin filament-associated proteins expressed in both smooth muscle and non-muscle cells. Whereas calponin-1 and calponin-2 have already been studied to some extent, little is known about the role of calponin-3 under physiological conditions due to the lack of an appropriate animal model. Here, we have used an unbiased screen to identify novel proteins implicated in signal transduction downstream of the precursor B cell receptor (pre-BCR) in B cells. We find that calponin-3 is expressed throughout early B cell development, localizes to the plasma membrane and is phosphorylated in a Syk-dependent manner, suggesting a putative role in pre-BCR signaling. To investigate this in vivo, we generated a floxed calponin-3-GFP knock-in mouse model that enables tracking of cells expressing calponin-3 from its endogenous promoter and allows its tissue-specific deletion. Using the knock-in allele as a reporter, we show that calponin-3 expression is initiated in early B cells and increases with their maturation, peaking in the periphery. Surprisingly, conditional deletion of the Cnn3 revealed no gross defects in B cell development despite this regulated expression pattern and the in vitro evidence, raising the question whether other components may compensate for its loss in lymphocytes. Together, our work identifies calponin-3 as a putative novel mediator downstream of the pre-BCR. Beyond B cells, the mouse model we generated will help to increase our understanding of calponin-3 in muscle and non-muscle cells under physiological conditions.
authors.affiliation: Department of Molecular Immunology, Max-Planck-Institut of Immunobiology and Epigenetics, Freiburg, Germany; Biology III, Faculty of Biology, Albert-Ludwigs-University Freiburg, Freiburg, Germany.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Flemming
authors.affiliation: Department of Medicine, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States of America.
authors.forename: Qi-Quan
authors.initials: QQ
authors.lastname: Huang
authors.affiliation: Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan, United States of America.
authors.forename: Jian-Ping
authors.initials: JP
authors.lastname: Jin
authors.affiliation: Department of Molecular Immunology, Max-Planck-Institut of Immunobiology and Epigenetics, Freiburg, Germany; Biology III, Faculty of Biology, Albert-Ludwigs-University Freiburg, Freiburg, Germany; BIOSS Centre for Biological Signalling Studies, Albert-Ludwigs-University Freiburg, Freiburg, Germany.
authors.forename: Hassan
authors.initials: H
authors.lastname: Jumaa
authors.affiliation: Department of Molecular Immunology, Max-Planck-Institut of Immunobiology and Epigenetics, Freiburg, Germany; Biology III, Faculty of Biology, Albert-Ludwigs-University Freiburg, Freiburg, Germany; BIOSS Centre for Biological Signalling Studies, Albert-Ludwigs-University Freiburg, Freiburg, Germany; Division of Developmental Immunology, Biocenter, Medical University Innsbruck, Innsbruck, Austria.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Herzog
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D055879:Gene Knock-In Techniques; D005822:Genetic Vectors / Q000235:genetics / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008840:Microfilament Proteins / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D015398:Signal Transduction; D000072377:Syk Kinase; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D000096985:Calponins
chemical_list: D002135:Calcium-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008840:Microfilament Proteins; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; D000096985:Calponins; C000606897:Syk protein, mouse