The superfamily of basic helix-loop-helix (bHLH) factors is strongly involved in brain development and neural stem cell specification. A subfamily of this huge family of transcription factors are the E-box factors, consisting of Tcf3, Tcf4, and Tcf12. We have shown that both Tcf4 and Tcf12 have a crucial role in the development of different cellular systems in the brain, like the cortex, corpus callosum and hippocampus (Tcf4), and mesodiencephalic dopaminergic neurons (Tcf4 and Tcf12).
Haplo-insufficiency of TCF4 in humans leads to Pitt-Hopkins syndrome, characterized by, amongst others, severe intellectual disability, typical facial gestalt, breathing abnormalities, and gastro-intestinal problems. By investigating the role of Tcf4 in brain development, we aim to gain more insight in the underlying molecular cascades and brain areas affected in Pitt-Hopkins syndrome patients, which is key to understanding this debilitating disease and in pinpointing possible therapeutic targets.
Our current research focuses mainly on the role of Tcf4 in brain development and can be divided into 2 different research lines
Next to this we have currently one research line running that focuses on Tcf12 in oligodendrogenesis
Pitt-Hopkins patients show severe breathing abnormalities in which they show periods of hyperventilation alternated with periods of severe hypoventilation or even complete absence of breathing. We hypothesize that one of the cuases of this problem may lie in an affected development of the medulla oblongata. This brain area is highly conserved between species and functions as a relay center in the regulation of vital cardiovascular, respiratory, and autonomic functions via highly specified medullary nuclei. The neurons that make up these nuclei originate from one (or more) of twelve specific progenitor zones in the medulla. As Tcf4 is expressed in the developing medulla oblongata, it may have a role in the correct development and functioning of these nuclei.
To gain more insight in the origin and development of the neurons in the different medullary nuclei we have mapped the development of these nuclei from progenitor to functional neuron. Based on this mapping and the expression of Tcf4 in the developing medulla we can make a proper estimation of which nuclei are dependent on Tcf4 for their development.
Defected myelination is one of the brain-specific characteristics in Pitt-Hopkins Syndrome patients. Myelination is crucial for neural functioning and communication. This proces is regulated by oligodendrocytes and continues until 21 years of age in humans. Next to this, it has been shown that mouse mutants with a Tcf4 mutation also show a defective myelin profile in the brain. We propose that Tcf4 is involved in the regulation of oligodendrogenesis and the ultimate maturation and functioning of oligodendrocytes. As oligodendrogenesis and myelination occurs relatively late during brain development and proceeds many years after birth, this would be a good starting point for a possible therapeutic target. With this research line we aim to gain more insight in the regulation of oligodendrogenesis by Tcf4 and investigate how Tcf4 regulates the generation of functioning oligodendrocytes and brain myelination.
Next to Tcf4 its direct family-member Tcf12 has been shown in few reports, to be expressed in oligodendrocytes and may have a role in oligodendrogenesis. Not much is known about a possible role for Tcf12 in this proces, but considering its close relation to Tcf4 and expression in OPCs there may be a role for this gene in this crucial proces. With this research line we aim to gain more insight into the role of Tcf12 in oligodendrogenesis and the possible combined regulation of E-box factors in this proces.