Electrical synapse structure requires distinct isoforms of a postsynaptic scaffold.

Electrical synapses are neuronal gap junction (GJ) channels associated with a macromolecular complex called the electrical synapse density (ESD), which regulates development and dynamically modifies electrical transmission. However, the proteomic makeup and molecular mechanisms utilized by the ESD that direct electrical synapse formation are not well understood. Using the Mauthner cell of zebrafish as a model, we previously found that the intracellular scaffolding protein ZO1b is a member of the ESD, localizing postsynaptically, where it is required for GJ channel localization, electrical communication, neural network function, and behavior. Here, we show that the complexity of the ESD is further diversified by the genomic structure of the ZO1b gene locus. The ZO1b gene is alternatively initiated at three transcriptional start sites resulting in isoforms with unique N-termini that we call ZO1b-Alpha, -Beta, and -Gamma. We demonstrate that ZO1b-Beta and ZO1b-Gamma are broadly expressed throughout the nervous system and localize to electrical synapses. By contrast, ZO1b-Alpha is expressed mainly non-neuronally and is not found at synapses. We generate mutants in all individual isoforms, as well as double mutant combinations in cis on individual chromosomes, and find that ZO1b-Beta is necessary and sufficient for robust GJ channel localization. ZO1b-Gamma, despite its localization to the synapse, plays an auxiliary role in channel localization. This study expands the notion of molecular complexity at the ESD, revealing that an individual genomic locus can contribute distinct isoforms to the macromolecular complex at electrical synapses. Further, independent scaffold isoforms have differential contributions to developmental assembly of the interneuronal GJ channels. We propose that ESD molecular complexity arises both from the diversity of unique genes and from distinct isoforms encoded by single genes. Overall, ESD proteomic diversity is expected to have critical impacts on the development, structure, function, and plasticity of electrical transmission.

Acute exposure to carbon monoxide inhalation and/or hot water immersion transiently increases erythropoietin in females but not in males.

The use of acute carbon monoxide inhalation (COi) and hot water immersion (HWI) are of growing interest as interventions to stimulate erythropoietin (EPO) production. However, whether EPO production is further augmented when combining these stressors and whether there are sex differences in this response are poorly understood. Therefore, we measured circulating EPO concentration in response to acute COi and HWI independently and in combination and determined whether the responses were altered by sex. Participants completed three study visits-COi, HWI, and combined COi and HWI-separated by 1 week in a randomized, balanced, crossover design. Renal blood velocity was measured during all interventions, and carboxyhaemoglobin was measured during and after COi. Serum samples were analysed every hour for 6 h post-intervention for EPO concentration. HWI decreased renal blood velocity (46.2 cm/s to 36.2 cm/s) (P < 0.0001), and COi increased carboxyhaemoglobin (1.5%-12.8%) (P < 0.0001) without changing renal blood velocity (46.4-45.2 cm/s) (P = 0.4456). All three interventions increased peak EPO concentration from baseline (COi: 6.02-9.74 mIU/mL; HWI: 6.80-11.10 mIU/mL; COi + HWI: 6.71-10.91 mIU/mL) (P = 0.0048) and to the same extent (P = 0.3505). On average, females increased EPO while males did not in response to COi (females: 6.17 mIU/mL; males: 1.27 mIU/mL) (P = 0.0010), HWI (females: 6.47 mIU/mL; males: 2.14 mIU/mL) (P = 0.0104), and COi and HWI (females: 6.65 mIU/mL; males: 1.76 mIU/mL) (P = 0.0256). These data emphasize that combining these interventions does not augment EPO secretion and that these interventions may work better in females.