PigK underlies macho behavior and is required for Rohon-Beard cell excitability

Abstract

The study of touch-evoked behavior allows investigation into the cells, circuits, and specific proteins and channels required for a tactile response. I investigated a mutant zebrafish strain, macho, lacking a touch response and with decreased sodium current amplitudes in sensory neurons. Mutant macho embryos carry a mutation in the pigk gene that is not present in wild type siblings. The pigk gene encodes the protein PigK that is critical for transfer of glycophosphatidylinositol anchors to precursor proteins. It is not understood how a mutation in pigk results in a decrease in sensory neuron sodium current amplitudes or touch response. I provided evidence that pigk is present at the right time to affect the touch response. My data suggests that maternal expression of pigk is a potential explanation for survival of macho mutants to larval stages. I next provided support for the identification of pigk as the gene underlying the macho phenotype through rescue with wild type pigk. I found that the touch response in macho mutants is rescued with ubiquitously expressed wild type pigk. I then expressed wild type pigk specifically in sensory neurons of macho mutants. I used electrophysiology to demonstrate that specific expression of wild type pigk resulted in rescue of voltage-gated sodium current amplitude and the ability to elicit action potentials. However, I found that expression of wild type pigk in these sensory neurons did not rescue the touch response. My work indicates the importance of pigk in the touch circuit, and reveals the need for pigk for more than normal function of INa and action potential firing in RB cells. I discuss potential future directions and implications for the study of the macho mutant and other mutants with decreased touch response.