Ultrastructural observations on rodlet-cell development in the head kidney of the southern platyfish, Xiphophorus maculatus (Teleostei: Poeciliidae)

Abstract

The enigmatic rodlet cell has been observed in tissues of marine and freshwater teleosts. The origin and function of this cell remain unclear. We describe the association of the rodlet cell with the head-kidney tissue of the southern platyfish, Xiphophorus maculatus. We have observed rodlet cells in various tissues of X. maculatus, e.g., the hemopoietic compartments of the head kidney, gill epithelia, and ovarian tissue, and in melanotic tumors. Recently, we found rodlet cells within the mesothelium and musculature. Intrigued by these observations, we began our current study of the rodlet cell – head kidney association in X. maculatus. We discerned a series of developmental stages of the rodlet cell within the hemopoietic tissue of the head kidney, including early precursor cells through degraded terminal stages. Tight junctions and desmosomes were observed between mature rodlet cells and endothelial cells. Desmosomal junctions were occasionally seen between maturing rodlet cells and neighboring cells within intertubular areas. We never observed junctional complexes between adjacent rodlet cells at any stage. Rodlet sacs were released intact and were seen to interact with other cellular components. We relate our findings to those of others who have described the development and distribution of rodlet cells in teleosts.