Volume 28, Issue 4

One of the major functions of our brain is to process spatial information and to make this information available to our motor systems to interact successfully with the environment. Numerous studies over the past decades and even centuries have investigated, how our central nervous system deals with this challenge. Spatial information can be derived from vision. We see, where the cup of coffee stands at the breakfast table or where the un-mute-button of our video-conference tool is. However, this is always just a snapshot, because the location of the projection of the cup or the un-mute-button shifts across the retina by each eye movement, i.e., 2–3 times per second. So, where exactly in space are objects located? And what signals guide self-motion and navigation through our environment? While also other sensory signals (vestibular, tactile, auditory, even smell) can help us localize objects in space and guide our navigation, here, we will focus on the dominant sense in primates: vision. We will review (i) how visual information is processed to eventually result in space perception, (ii) how this perception is modulated by action, especially eye movements, at the behavioral and at the neural level, and (iii) how spatial representations relate to other encodings of magnitude, i.e., time and number.

“Blindness separates from things; deafness separates from people.” This quote attributed to the deaf-blind author and activist Helen Keller (1880–1968) indicates the importance of proper hearing for social interaction in our society which is largely driven by acoustic communication. A major cause for auditory dysfunction lies in our genome with currently more than 100 genes linked to hearing loss. One example is the microRNA gene Mir-96 of the microRNA-183 family. MicroRNAs are small regulatory RNAs involved in the finetuning of gene expression. Analyses of transgenic mouse models established this microRNA family as a major regulator for the function of the inner ear as well as synaptic transmission in the auditory brainstem. The microRNA-183 family might therefore play an important role in coordinating the development of the peripheral and central auditory system and their specializations.

Familial adult myoclonic epilepsy (FAME) is a rare autosomal dominant disorder characterized by cortical myoclonic tremor and seizures. FAME has been mapped to chromosomes (chr) 2, 3, 5 and 8, but the cause has remained elusive for more than a decade. An expansion of intronic TTTTA and TTTCA repeats in SAMD12 was identified as the cause of FAME1 in Japanese families linked to chr 8 in 2018. This discovery triggered the identification of identical repeat expansions at five additional loci (FAME2: STARD7 ; FAME3: MARCHF6 ; FAME4: YEATS2 ; FAME6: TNRC6A and FAME7: RAPGEF2 ). These genes encode proteins with different functions and subcellular localizations and their expression is unaltered in available peripheral tissues, suggesting that the expansion is pathogenic independently of the gene itself. The pathophysiological mechanisms are not yet known but possibly include toxicity at the RNA level or translation of toxic polypeptides from the repeats, a mechanism known as repeat-associated non-AUG (RAN) translation. FAME is a paradigm of human genetic disorder caused by a non-coding expansion unrelated to the gene where it occurs.

Patients carrying pathogenic gene variants encoding factors linked to the sonic hedgehog (SHH) pathway suffer from severe congenital brain malformations including holoprosencephaly (HPE). A poorly understood feature of these common anomalies is the highly variable penetrance, even amongst family members, carrying the same mutation. Modifier genes–genetic variants that can affect the phenotypic outcome of the primary disease-causing gene–contribute to this variability within pedigrees. Modifier genes can confer resilience or susceptibility to a disease, but are difficult to identify in humans. Studying the complex genetic interactions in mouse models of human congenital disorders can be instrumental in the identification of genes, that powerfully modulate SHH signaling pathway capacity and ultimately the penetrance of genetic disturbances. Understanding the underlying complex molecular mechanisms of disease aetiology and can support directing future genetic linkage studies in humans.