Signalling through phospholipase C beta 4 is not essential for midbrain dopaminergic neuron survival

MYT1 role in the microtia-craniofacial microsomia spectrum

Background

Craniofacial microsomia (CFM), also known as the oculo‐auriculo‐vertebral spectrum, comprises a variable phenotype with the most common features including microtia and mandibular hypoplasia on one or both sides, in addition to lateral oral clefts, epibulbar dermoids, cardiac, vertebral, and renal abnormalities. The etiology of CFM is largely unknown. The MYT1 gene has been reported as a candidate based in mutations found in three unrelated individuals. Additional patients with mutations in this gene are required to establish its causality. We present two individuals with CFM that have rare variants in MYT1 contributing to better understand the genotype and phenotype associated with mutations in this gene.

Methods/Results

We conducted genetic analysis using whole‐exome and ‐genome sequencing in 128 trios with CFM. Two novel MYT1 mutations were identified in two participants. Sanger sequencing was used to confirm these mutations.

Conclusion

We identified two additional individuals with CFM who carry rare variants in MYT1, further supporting the presumptive role of this gene in the CFM spectrum.

Specific vulnerability of substantia nigra compacta neurons

The specific loss of substantia nigra compacta (SNc) neurons in Parkinson's disease (PD) has been the main driving force in initiating research efforts to unravel the apparent SNc-specific vulnerability. Initially, metabolic constraints due to high dopamine turnover have been the main focus in the attempts to solve this issue. Recently, it has become clear that fundamental differences in the molecular signature are adding to the neuronal vulnerability and provide specific molecular dependencies. Here, the different processes that define the molecular background of SNc vulnerability are summarized.

Signalling pathways underlying neural cell adhesion molecule-mediated survival of dopaminergic neurons

Stimulation of the neural cell adhesion molecule (NCAM) by homophilic interactions is known to lead to neurite outgrowth as well as to neuronal survival. Whereas a complex network of signalling molecules is known to be of importance to NCAM-mediated neurite extension, only limited information is available regarding signalling underlying NCAM-mediated neuroprotection. Here, we present data suggesting a difference in the signalling events required for survival of rat dopaminergic neurons as compared with neurite outgrowth from the same cell type. Whereas Fyn, fibroblast growth factor receptor, mitogen-activated protein and ERK kinase, protein kinase A and protein kinase C are required for both responses to NCAM-induced signalling, phospholipase C and Ca(2+)-calmodulin-dependent kinase II are only necessary for the neurite outgrowth response, but dispensable for neuroprotection.

Strategies to unravel molecular codes essential for the development of meso-diencephalic dopaminergic neurons

Understanding the development of neuronal systems has become an important asset in the attempt to solve complex questions about neuropathology as found in Parkinson's disease, schizophrenia and other complex neuronal diseases. The development of anatomical and functional divergent structures in the brain is achieved by a combination of early anatomical patterning and highly coordinated neuronal migration and differentiation events. Fundamental to the existence of divergent structures in the brain is the early region-specific molecular programming. Neuronal progenitors located along the neural tube can still adapt many different identities. Their exact position in the developing brain, however, determines early molecular specification by region-specific signalling molecules. These signals determine time and region-specific expression of early regulatory genes, leading to neuronal differentiation. Here, we focus on a well-described neuronal group, the meso-diencephalic dopaminergic neurons, of which heterogeneity based on anatomical position could account for the difference in vulnerability of specific subgroups as observed in Parkinson's disease. The knowledge of their molecular coding helps us to understand how the meso-diencephalic dopaminergic system is built and could provide clues that unravel mechanisms associated with the neuropathology in complex diseases such as Parkinson's disease.