Tropomyosin and alpha‐actinin in teleost rodlet cells

Abstract

AbstractRodlet cells are a distinctive pear‐shaped cell type unique to the epithelium of teleost fishes. Thick submembranous smooth muscle‐like cortex, or fibrous capsule, envelopes the rodlet cell. The cortex undergoes contraction resulting in the expulsion of intracellular contents through an apical pore and out into the extracellular environment. The present study evaluated the distribution of tropomyosin in rodlet cells. In addition, distribution of alpha‐actinin was revisited in a previous study using a modified immunostaining protocol. Alpha‐actinin was localized to the fibrous capsule predominantly in a partial fibrillar pattern reminiscent of dense plaques of smooth muscle. In contrast, tropomyosin was localized as dot‐ and patch‐like accumulations within the cortex. Tropomyosin was also found as a closely packed arrangement of intensely stained dots at the apical pore of rodlet cells, distinct from its location in the cortex. The findings support a smooth muscle‐like nature to the rodlet cell cortex and suggest a novel role for tropomyosin in capping the apical pore.