02197nas a2200205 4500008004100000022002500041245012900066210006900195260001600264490000800280520153300288653002201821653001601843653001501859653001601874653001701890100002201907700002301929856003901952 2025 eng d a0022-0949, 1477-914500aGene expression correlates and mechanistic insights into electric organ discharge duration changes in mormyrid electric fish0 aGene expression correlates and mechanistic insights into electri cJun-01-20250 v2283 a

Electric organ discharge (EOD) duration in African weakly electric fish (Mormyridae) is the most variable waveform component between species and the basis for distinguishing species-specific signals. EOD duration is thought to be influenced by morphological and physiological features of electrocytes (the cells that comprise the electric organ), but the mechanistic details are poorly understood. It has long been known that EOD duration is modulated by androgen hormones, affording an opportunity to identify gene expression correlates of EOD duration differences. We induced EOD elongation in the mormyrid Brienomyrus brachyistius by administering 17α-methyltestosterone (17αMT) to three treatment groups: control (no 17αMT exposure), T1day and T8day (samples taken 1 and 8 days after a single exposure to 17αMT, respectively). We then performed RNAseq, differential gene expression and functional enrichment analysis to detect gene expression changes during EOD duration change. Our analyses indicate 44 genes whose expression changed in tandem with EOD elongation and include genes responsible for actin filaments and microtubules, extracellular matrix organization and membrane lipid metabolism. Additionally, we found expression changes in one Na+ channel β-subunit, and five voltage-gated K+ channels. Together, these genes point toward specific cellular processes that contribute to morphological and physiological changes that contribute to EOD duration changes.

10aAndrogen hormones10aelectrocyte10aK+ channel10aNa+ channel10aTestosterone1 aLosilla, Mauricio1 aGallant, Jason, R. uhttps://doi.org/10.1242/jeb.24954802679nas a2200241 4500008004100000022002500041245011900066210006900185260001600254300000900270520193000279653001602209653002402225653001602249653001202265653002002277653001602297100001802313700001602331700002202347700002102369856004702390 2024 eng d a0302-766X, 1432-087800aOrganization of the stalk system on electrocytes in mormyrid weakly electric fish Campylomormyrus compressirostris0 aOrganization of the stalk system on electrocytes in mormyrid wea cDec-20-2024 a1-173 a

The adult electric organ in weakly electric mormyrid fish consists of action-potential-generating electrocytes, structurally and functionally modified skeletal muscle cells. The electrocytes have a disc-shaped portion and, on one of its sides, numerous thin processes, termed stalklets. These unite to stalks leading to a single main stalk that carries the innervation site. Here, we describe the 3-dimensional layout of the stalklet/stalk system in adult Campylomormyrus compressirostris by differential interference contrast microscopy and confocal fluorescence microscopy. Using antibodies against Na+/K+-ATPase α-subunit and plasma membrane Ca2+-ATPase, we show that these ion pumps are differentially distributed over the stalklet/stalk system, with plasma membrane Ca2+-ATPase being enriched on the stalklet membrane. Stalklets are distributed and organized in a quite uniform pattern on the posterior face of the electrocyte disc and fuse to terminal stalks. The latter then unite in a mostly dichotomic mode to stalks of increasing thickness, with the main stalk measuring about 100 µm in diameter. We further analyse the structural organization of stalklets and stalks, with a characteristic cytoskeletal system of bundled actin filaments in the centre and nuclei in subsurface position. These results suggest that the stalklet/stalk system is adapted in its structural layout to generate an action potential highly synchronized over the entire disc-portion of the electrocyte, accounting for the short electric organ discharge in this species. Our results suggest that actin-related proteins overexpressed in electrocytes, as shown previously by transcriptome analysis, may be involved in the organization of the unique F-actin system in stalklets and stalks.

10aCa2+-ATPase10aConfocal microscopy10aelectrocyte10aF-actin10aPlasma membrane10aSodium pump1 aBaumann, Otto1 aCheng, Feng1 aKirschbaum, Frank1 aTiedemann, Ralph uhttps://doi.org/10.1007/s00441-024-03938-y01771nas a2200217 4500008004100000022001400041245006900055210006500124260001600189300001000205490000800215520117700223653001701400653001601417653000801433653001701441100001701458700001701475700002001492856004101512 1976 eng d a0302-982400aThe electric organ of a mormyrid as a current and voltage source0 aelectric organ of a mormyrid as a current and voltage source cJan-01-1976 a65-880 v1103 a

We have examined how the electric organ discharge (EOD) of a mormyrid (Gnathonemus petersii) is affected by changes in resistive load (Figs. 3, 4, 5). We have also shown how this load depends on resistivity and distance to non-conducting boundaries (Figs. 10, 11). When resistive load was varied, voltage and current were related in a linear, battery-like manner for the initial, head positive phase of the EOD (Figs. 4, 5). This linear relation made it possible to estimate first phase e.m.f, and source resistance. For the second, head negative phase, however, voltage rose to a peak and then fell as resistance increased. Furthermore, the waveform of the second but not the first phase was strongly affected by load changes. These second phase features were shown to reflect a dependence of second phase e.m.f, on first phase current. A linear and battery-like relation between second phase voltage and current was seen when first phase load was held constant while varying second phase load (Fig. 6). These results on the behavior of the whole electric organ can be understood in terms of the underlying properties of the cellular generators, the electrocytes

10aconductivity10aelectrocyte10aEOD10aeod waveform1 aBell, C., C.1 aBradbury, J.1 aRussell, C., J. uhttp://dx.doi.org/10.1007/bf00656782