RESUMO
The quality and quantity of BCR signals impact on cell fate decisions of B lymphocytes. Here, we describe novel gene-targeted mice, which in the context of normal VDJ recombination show hypomorphic expression of immunoglobulin µ heavy chain (µHC) mRNA levels and hence lower pre-BCR and BCR levels. Hypomorphic expression of µHC leads to augmented selection processes at all stages of B-cell development, noticeably at the expansion of pre-B cells, the positive selection of immature B lymphocytes in the bone marrow and the selection of the follicular (FO), marginal zone (MZ) and B1 B-lymphocyte compartment in peripheral lymphoid organs. Immature as well as mature FO and MZ B lymphocytes in the peripheral lymphoid organs express lower levels of the receptor for B-cell activating factor (BAFF). In addition, hypomorphic expression of the BCR favours receptor editing. Together, our results highlight the critical importance of pre-BCR and BCR receptor levels for the normal development of B-lymphocyte subpopulations in the context of intact VDJ recombination and a diverse antibody repertoire.
Assuntos
Subpopulações de Linfócitos B/fisiologia , Diferenciação Celular/imunologia , Genes de Cadeia Pesada de Imunoglobulina/fisiologia , Receptores de Antígenos de Linfócitos B/imunologia , Receptores de Antígenos de Linfócitos B/metabolismo , Alelos , Animais , Formação de Anticorpos/genética , Formação de Anticorpos/fisiologia , Receptor do Fator Ativador de Células B/metabolismo , Subpopulações de Linfócitos B/metabolismo , Células da Medula Óssea/imunologia , Células da Medula Óssea/metabolismo , Células da Medula Óssea/fisiologia , Diferenciação Celular/genética , Células Cultivadas , Genes de Cadeia Pesada de Imunoglobulina/genética , Cadeias mu de Imunoglobulina/genética , Cadeias mu de Imunoglobulina/metabolismo , Lectinas/genética , Lectinas/imunologia , Lectinas/metabolismo , Camundongos , Camundongos Transgênicos , Células Precursoras de Linfócitos B/imunologia , Células Precursoras de Linfócitos B/metabolismo , Células Precursoras de Linfócitos B/fisiologia , Receptores de Antígenos de Linfócitos B/genética , Lectinas Semelhantes a Imunoglobulina de Ligação ao Ácido SiálicoRESUMO
Annexins are highly conserved proteins that are characterized by their ability to interact with phospholipids in a calcium-dependent manner. Although diverse functions have been ascribed to annexins based on in vitro analyses, their in vivo functions still remain unclear. The intensively studied annexin A5 has been identified by its effects on blood coagulation, and subsequently, its function as a calcium-specific ion channel was described. In vitro experiments and expression studies suggested a potential role of annexin A5 during calcification processes in vivo, especially in endochondral ossification. To gain insights into the relevance of annexin A5 in this process, we generated an annexin A5-deficient mouse mutant. Mice lacking annexin A5 are viable, are fertile, and reveal no significant alterations in the biochemical parameters characteristic for metabolic or functional defects. Neither the development of skeletal elements nor the in vitro calcification properties of isolated chondrocytes is significantly impaired by the absence of annexin A5. Therefore, annexin A5 is dispensable for the formation and maintenance of skeletal elements in the mouse and may possibly be pointing to a compensatory effect of other members from the annexin family due to their high functional and structural similarity.
Assuntos
Anexinas/fisiologia , Desenvolvimento Ósseo/fisiologia , Animais , Animais Recém-Nascidos , Anexina A5 , Anexinas/deficiência , Anexinas/genética , Desenvolvimento Ósseo/genética , Calcificação Fisiológica/genética , Condrócitos/metabolismo , Marcação de Genes , Imuno-Histoquímica , Técnicas In Vitro , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , FenótipoRESUMO
We examined the molecular progression of ectopic bone development upon application of recombinant human bone morphogenetic protein-2 (rhBMP2), using a commercial collagen type I carrier, in the hind quarter muscles of mice. We performed a gene expression study using mRNA in situ hybridisation to compare embryonic cartilage and bone formation with BMP2-induced ectopic bone formation. As bone growth can be induced postnatally or in adult animals, we examined the expression of molecules regulating embryonic bone development. We found that the mRNAs of the same molecules, such as Indian hedgehog (IHH), parathyroid hormone (PTH)/PTH-related peptide receptor (PPR) and BMPs, that regulate embryonic cartilage and bone development, are expressed during BMP-induced ectopic bone formation, suggesting parallels in the mechanisms controlling these processes. Our studies support by molecular means the previous findings in rats that BMP2-induced ectopic bone formation in mice undergoes bone development involving both modes, endochondral and intramembranous ossification, simultaneously at different sites of the implant.