A functional and molecular approach to study novel human and primate specific N-Ank superfamily members and their involvement in modulating membrane topologies and shaping human neurons

• Applicant: Dr. Maria Schörnig
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells ; Cell Biology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 513225299

Primates and especially humans stand out in comparison to other mammals as they have larger brains and cortices with a higher number of cortical neurons and a high neuronal connectivity. Neurons need to adopt a specific morphology to form tightly connected neuronal networks. Likewise important, neuronal networks have the great ability to constantly change trough growth and reorganization, the so-called neuronal plasticity, which requires tremendous changes of the neuronal membrane morphology. So far, no human or primate specific gene could be identified that is involved in specifically mediating the dynamic, highly branched morphology of human neurons. Recently a new class of membrane shaping proteins has been identified, which was termed the N-Ank protein superfamily. The N-Ank proteins use a combination of their ankyrin repeat array and an amino (N)-terminal amphipathic helix to bind and shape membranes. In rodents, ankycorbin, a novel ankyrin repeat protein (N-Ank), is such a membrane shaper, able to bind to and shape the neuronal plasma membrane, increase the number of dendrites and change the branching pattern of rodent neurons. Surprisingly, we found a high variety of primate and ape specific N-Ank family members that consequently arose very recently in evolution on the hominin lineage. We hypothesize that the primate specific N-Ank proteins might fulfill specialized distinct functions in membrane shaping of human and primate neurons. To identify candidate proteins for this role, we studied the expression of ape and primate specific N-Ank genes using single cell RNA sequencing and RT-qPCR in human iPSC derived neurons (iNeurons). We found ANKRD18A, ANKRD18B, ANKRD36A, ANKRD36B and ANKRD36C expressed in human iNeurons, making these five proteins promising candidates for shaping human neuron membranes. This project proposes to address a putative loss-of-function of the membrane shaper ankycorbin in humans and a potential replacement of its functions by primate specific N-Ank proteins in human neurons. Therefore, we aim at characterizing the ape- and primate-specific N-Ank proteins ANKRD18A, ANKRD18B, ANKRD36A, ANKRD36B and ANKRD36C in comparison to human ankycorbin. We aim at identifying molecular causes of the functional diversity and possible specificity of the five human N-Ank proteins and define the distinct functional roles of these N-Ank proteins in human neuron membrane shaping and neuronal morphogenesis. Thereby, we hope to understand the evolutionary development of the primate specific N-Ank proteins. By identifying proteins that have functional consequences in human neurons we hope to understand some of the key biological predispositions that made human cognitive abilities possible. Such changes may also offer new inroads into understanding diseases that affect human-specific cognition.

• DFG Programme: Research Grants