Marek Dudas

Cardiac outflow tract defects in mice lacking ALK2 in neural crest cells

Cardiac neural crest cells are multipotent migratory cells that contribute to the formation of the cardiac outflow tract and pharyngeal arch arteries. Neural crest-related developmental defects account for a large proportion of congenital heart disorders. Recently, the genetic bases for some of these disorders have been elucidated, and signaling pathways required for induction, migration and differentiation of cardiac neural crest have emerged. Bone morphogenetic proteins comprise a family of secreted ligands implicated in numerous aspects of organogenesis, including heart and neural crest development. However, it has remained generally unclear whether BMP ligands act directly on neural crest or cardiac myocytes during cardiac morphogenesis, or function indirectly by activating other cell types. Studies on BMP receptor signaling during organogenesis have been hampered by the fact that receptor knockouts often lead to early embryonic lethality. We have used a Cre/loxP system for neural crest-specific deletion of the type I receptor, ALK2, in mouse embryos. Mutant mice display cardiovascular defects, including persistent truncus arteriosus, and abnormal maturation of the aortic arch reminiscent of common forms of human congenital heart disease. Migration of mutant neural crest cells to the outflow tract is impaired, and differentiation to smooth muscle around aortic arch arteries is deficient. Moreover, in Alk2 mutants, the distal outflow tract fails to express Msx1, one of the major effectors of BMP signaling. Thus, the type I BMP receptor ALK2 plays an essential cell-autonomous role in the development of the cardiac outflow tract and aortic arch derivatives.

Craniofacial defects in mice lacking BMP type I receptor Alk2 in neural crest cells

Neural crest cells (NCCs) are pluripotent migratory cells that contribute to the development of various craniofacial structures. Many signaling molecules have been implicated in the formation, migration and differentiation of NCCs including bone morphogenetic proteins (BMPs). BMPs signal through a receptor complex composed of type I and type II receptors. Type I receptors (Alk2, Alk3 and Alk6) are the primary determinants of signaling specificity and therefore understanding their function is important in revealing the developmental roles of molecular pathways regulated by BMPs. Here we used a Cre/loxP system for neural crest specific deletion of Alk2. Our results show that mice lacking Alk2 in the neural crest display multiple craniofacial defects including cleft palate and a hypotrophic mandible. Based on the present results we conclude that signaling via Alk2 receptors is non-redundant and regulates normal development of a restricted set of structures derived from the cranial neural crest.

Defective ALK5 signaling in the neural crest leads to increased postmigratory neural crest cell apoptosis and severe outflow tract defects.

BackgroundCongenital cardiovascular diseases are the most common form of birth defects in humans. A substantial portion of these defects has been associated with inappropriate induction, migration, differentiation and patterning of pluripotent cardiac neural crest stem cells. While TGF-β-superfamily signaling has been strongly implicated in neural crest cell development, the detailed molecular signaling mechanisms in vivo are still poorly understood.ResultsWe deleted the TGF-β type I receptor Alk5 specifically in the mouse neural crest cell lineage. Failure in signaling via ALK5 leads to severe cardiovascular and pharyngeal defects, including inappropriate remodeling of pharyngeal arch arteries, abnormal aortic sac development, failure in pharyngeal organ migration and persistent truncus arteriosus. While ALK5 is not required for neural crest cell migration, our results demonstrate that it plays an important role in the survival of post-migratory cardiac neural crest cells.ConclusionOur results demonstrate that ALK5-mediated signaling in neural crest cells plays an essential cell-autonomous role in the pharyngeal and cardiac outflow tract development.

Transforming growth factor‐β3 affects plasminogen activator inhibitor‐1 expression in fetal mice and modulates fibroblast‐mediated collagen gel contraction

For over two decades, the precise role of transforming growth factor‐β (TGF‐β) isoforms in scarless healing of mammalian fetal skin wounds has generated much interest. Although their exact role remains to be established, it has been suggested that high TGF‐β3 activity may correlate with a scarless phenotype. Previously, we showed that plasminogen activator inhibitor‐1 (PAI‐1), a known TGF‐β downstream molecule and marker of fibrosis, is also developmentally regulated during fetal skin development. In this study, the relationship between TGF‐β3 and PAI‐1 was investigated using embryonic day 14.5 TGF‐β3 knockout (ko) mice. The results showed increased PAI‐1 expression in the epidermis and dermis of ko mice, using an ex vivo limb‐wounding study. Furthermore, increased PAI‐1 expression and activity was seen in embryo extracts and conditioned media of ko dermal fibroblasts. When TGF‐β3 knockout fibroblasts were placed into three‐dimensional collagen matrices, they were found to have decreased collagen gel contraction, suggesting altered cell–matrix interaction. These findings provide a further avenue for the interactive role of TGF‐β3 and PAI‐1 during fetal scarless repair.

TGF-β Superfamily and Mouse Craniofacial Development: Interplay of Morphogenetic Proteins and Receptor Signaling Controls Normal Formation of the Face

Publisher Summary This chapter discusses the role of members of the transforming growth factor-β (TGF-β) super family and their signaling pathways in facial development. The discovery of bone morphogenetic proteins (BMPs) was instigated by the observation that ectopic bone was formed in fascia that had been used during surgery to bridge large gaps in the urinary bladder. This was followed by the discovery that, in addition to urinary epithelium, demineralized bone also possesses osteogenic capability when transplanted into connective tissues. Based on their abundance and expression pattern, BMPs and growth and differentiation factors (GDFs) represent a heterogeneous group of growth factors sharing the same receptors in a complicated manner that is poorly understood. Based on the sequence homology and similarities in physiological behavior, these ligands are currently sorted into eight groups, but this sorting should be considered approximate and not final. The BMP–GDF signaling logic during development is difficult to understand, and the current knowledge is very fragmented, composed of hundreds of mutually unconnected observations coming from multiple animal species, developmental stages, and practically all organ systems. Germline mutations, somatic mutations, and polymorphisms of genes related to TGF-β signaling lead to various diseases in humans. In addition to developmental malformations, a large portion of TGF-β superfamily signaling research is devoted to cancer. Some human ‘‘TGF-β’’ diseases have phenotypic features similar to those described in rodent knockout models, but many others are quite different.

Tripolar mitosis in human cells and embryos: Occurrence, pathophysiology and medical implications

Tripolar mitosis is a specific case of cell division driven by typical molecular mechanisms of mitosis, but resulting in three daughter cells instead of the usual count of two. Other variants of multipolar mitosis show even more mitotic poles and are relatively rare. In nature, this phenomenon was frequently observed or suspected in multiple common cancers, infected cells, the placenta, and in early human embryos with impaired pregnancy-yielding potential. Artificial causes include radiation and various toxins. Here we combine several pieces of the most recent evidence for the existence of different types of multipolar mitosis in preimplantation embryos together with a detailed review of the literature. The related molecular and cellular mechanisms are discussed, including the regulation of centriole duplication, mitotic spindle biology, centromere functions, cell cycle checkpoints, mitotic autocorrection mechanisms, and the related complicating factors in healthy and affected cells, including post-mitotic cell-cell fusion often associated with multipolar cell division. Clinical relevance for oncology and embryo selection in assisted reproduction is also briefly discussed in this context.

Signaling through Tgf-β type I receptor Alk5 is required for upper lip fusion

Cleft lip with or without cleft palate is one of the most common congenital malformations in newborns. While numerous studies on secondary palatogenesis exist, data regarding normal upper lip formation and cleft lip is limited. We previously showed that conditional inactivation of Tgf-beta type I receptor Alk5 in the ectomesenchyme resulted in total facial clefting. While the role of Tgf-beta signaling in palatal fusion is relatively well understood, its role in upper lip fusion remains unknown. In order to investigate a role for Tgf-beta signaling in upper lip formation, we used the Nes-Cre transgenic mouse line to delete the Alk5 gene in developing facial prominences. We show that Alk5/Nes-Cre mutants display incompletely penetrant unilateral or bilateral cleft lip. Increased cell death seen in the medial nasal process and the maxillary process may explain the hypoplastic maxillary process observed in mutants. The resultant reduced contact is insufficient for normal lip fusion leading to cleft lip. These mice also display retarded development of palatal shelves and die at E15. Our findings support a role for Alk5 in normal upper lip formation not previously reported.