Ventral-to-dorsal electrocyte development in electric organs of electric eel (Electrophorus)

Electric eels (Electrophorus) are renowned for their ability to generate electric discharge, which is used for prey capture and defense. Their electric organs (EOs) are located along the lateral-ventral region of the tail and contain electrocytes, which are multinucleated syncytium cells. The developmental origin of the electrocyte is mesodermal lineage cells observed in the ventral part of the myotome. However, it is unclear whether these precursor cells are also maintained in later stages and contribute to electric organ growth in adulthood. In this study, we report regional differences in cell morphology within the main EO (mEO) and identify a candidate cell population for electrocyte progenitors at the juvenile stages of Electrophorus. The cell morphology and distribution from the ventral terminal to the dorsal region of the mEO suggest the segregation of progenitors from the ventral cluster and their gradual transformation into mature multinucleated electrocytes via cell fusion and layering along the dorsal axis. Immunohistochemistry revealed strong expression of sodium-potassium adenosine triphosphatase (Na⁺/K⁺-ATPase), a key component in generating electric discharge in the mEO, across most mEO regions, except in the ventral cluster cells. Based on these observations, we propose that electrocyte progenitors develop from ventral cluster cells in the mEO and differentiate into mature multinucleated cells as they migrate dorsally. This is the first report to approach the developmental process of Electrophorus electrocytes from cell morphology and genetic profiles. Our findings represent a breakthrough in understanding the differentiation of electrocytes during the growth stages of Electrophorus.