Inactivation of Sonic Hedgehog Signaling and Polydactyly in Limbs of Hereditary Multiple Malformation, a Novel Type of Talpid Mutant

Multiple Cell Lineages Give Rise to a Cell Type

It has long been assumed that a specific cell type arises following stepwise specification of cells corresponding to the branching of cell lineages. However, accumulating evidence indicates that multiple and even remote cell lineages can lead to the development of the same cells. Four examples giving different yet new insights will be discussed: skeletal muscle development from precursors with distinct initial histories of transcriptional regulation, lens cell development from remote lineages yet sharing basic transcription factors, blood cell development under intersectional pathways, and neural tissue development from cardiac precursors through the manipulation of just one component of epigenetic regulation. These examples provide flexible and nondogmatic perspectives on developmental cell regulation, fundamentally revising the old model relying on cell lineages.

Two nonsense GLI3 variants are associated with polydactyly and syndactyly in two families by affecting the sonic hedgehog signaling pathway

Background

Polydactyly and syndactyly are congenital limb deformities, segregating in an autosomal‐dominant fashion. The variants in the GLI3 gene are closely related to congenital limb malformations. However, the causes underlying polydactyly and syndactyly are not well understood.

Methods

We conducted a whole‐exome sequencing on two four‐generation Chinese families with polydactyly and syndactyly. Then c.2374C>T and c.1728C>A mutant plasmids were transfected to HEK293T cells and mice limb bud cells to explore the functional consequences of these variants. Western blot and real‐time quantitative PCR were used to analyze the expression of GLI3 and Shh.

Results

In these two families, the known GLI3 variant (NM_000168.6:c.2374C>T) and the novel GLI3 variant (NM_000168.6:c.1728C>A) contributed to polydactyly and syndactyly. Additionally, the GLI3 c.2374C>T mutant plasmid led to truncated GLI3 protein, and the GLI3 c.1728C>A mutant plasmid led to degraded GLI3 protein. Simultaneously, we demonstrated that the GLI3‐mutant plasmids led to decreased Shh expression in mice limb bud cells.

Conclusion

We demonstrated that the novel GLI3 variant (c.1728C>A) and known GLI3 variant (c.2374C>T) contributed to the malformations in two four‐generation pedigrees with polydactyly and syndactyly by affecting SHH signaling.

We demonstrated that the novel GLI3 variant (c.1728C>A) and known GLI3 variant (c.2374C>T) contributed to the malformations in two four‐generation pedigrees with polydactyly and syndactyly by affecting SHH signaling.

TALPID3/KIAA0586 Regulates Multiple Aspects of Neuromuscular Patterning During Gastrointestinal Development in Animal Models and Human

TALPID3/KIAA0586 is an evolutionary conserved protein, which plays an essential role in protein trafficking. Its role during gastrointestinal (GI) and enteric nervous system (ENS) development has not been studied previously. Here, we analyzed chicken, mouse and human embryonic GI tissues with TALPID3 mutations. The GI tract of TALPID3 chicken embryos was shortened and malformed. Histologically, the gut smooth muscle was mispatterned and enteric neural crest cells were scattered throughout the gut wall. Analysis of the Hedgehog pathway and gut extracellular matrix provided causative reasons for these defects. Interestingly, chicken intra-species grafting experiments and a conditional knockout mouse model showed that ENS formation did not require TALPID3, but was dependent on correct environmental cues. Surprisingly, the lack of TALPID3 in enteric neural crest cells (ENCC) affected smooth muscle and epithelial development in a non-cell-autonomous manner. Analysis of human gut fetal tissues with a KIAA0586 mutation showed strikingly similar findings compared to the animal models demonstrating conservation of TALPID3 and its necessary role in human GI tract development and patterning.

Hedgehog Signaling and Embryonic Craniofacial Disorders

Since its initial discovery in a Drosophila mutagenesis screen, the Hedgehog pathway has been revealed to be instrumental in the proper development of the vertebrate face. Vertebrates possess three hedgehog paralogs: Sonic hedgehog (Shh), Indian hedgehog (Ihh), and Desert hedgehog (Dhh). Of the three, Shh has the broadest range of functions both in the face and elsewhere in the embryo, while Ihh and Dhh play more limited roles. The Hedgehog pathway is instrumental from the period of prechordal plate formation early in the embryo, until the fusion of the lip and secondary palate, which complete the major patterning events of the face. Disruption of Hedgehog signaling results in an array of developmental disorders in the face, ranging from minor alterations in the distance between the eyes to more serious conditions such as severe clefting of the lip and palate. Despite its critical role, Hedgehog signaling seems to be disrupted through a number of mechanisms that may either be direct, as in mutation of a downstream target of the Hedgehog ligand, or indirect, such as mutation in a ciliary protein that is otherwise seemingly unrelated to the Hedgehog pathway. A number of teratogens such as alcohol, statins and steroidal alkaloids also disrupt key aspects of Hedgehog signal transduction, leading to developmental defects that are similar, if not identical, to those of Hedgehog pathway mutations. The aim of this review is to highlight the variety of roles that Hedgehog signaling plays in developmental disorders of the vertebrate face.