Origin of Rodlet Cells and Mapping Their Distribution in Ruby-Red-Fin Shark

What is it about?

The present study describes for the first time histology, histochemistry, and ultrastructure of all rodlet stages. By ultrastructure, we identified rodlet progenitors in the stroma of the olfactory organ in Red-Fin shark. Rodlet progenitors were mesenchymal-like cells synthesis the primitive rodlet granules. Rodlet progenitors differentiated to vesicular rodlet cells, which was rich in vesicles and vacuoles, and accumulate intracellular fibrillar-like components. Granular rodlet cells were observed in the basal epithelia, contained premature rodlet granules and began to organize the fibrillar components of the rodlet capsule. Transitional rodlet cells continued to deposit the fibrils of the capsule and synthesis of rodlet granules. Mature rodlet cells were polarized bear-shape and had typical rodlet granules. Histochemistry showed rodlet cells had a wide range of staining affinities including carbohydrate, lipid, and protein staining. All stages of rodlet cells revealed the presence of PAS-positive granules in the cytoplasm of rodlet cells where, While the ruptured ones stained strongly with alcian blue, sliver stain and Sudan black B. Rodlet granule was positive for bromophenol blue Rodlet cells were positively immunostained against Matrix Metalloproteinase-9 (MPP-9) in all stages indicate invasion properties of rodlet cells in tissue. Conclusion rodlet cells originated from the stroma of the olfactory organ.

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Why is it important?

Two possible pathways could be suggested for rodlet migration from the respiratory tract to other organs in the body. Immature rodlet could penetrate the wall of one of the branches of the efferent branchial vessels which circulate to the blood and distribute to the other organs. The second pathway; rodlet cells could penetrate through the walls of the respiratory organs in the body cavity to migrate to other organs. Immature stage (particularly granular stage) presented in the connective tissue of these organs and rodlet maturation occurred either in the connective tissue of the organs or in the epithelium of the tubular organs and skin. Different stages of rodlet cells were identified. Rodlet progenitor appeared as a Mesenchymal-like cell which transformed into vesicular, granular, transitional, mature, and ruptured stages. Rodlet progenitors were detected in the olfactory organs the red-finned shark while granular, transitional, mature, and ruptured were observed in other organs. They expressed MMP-9 which degrade the matrix components and permit their penetration and localization in other organs and tissues. Rodlet cells have histochemical staining affinity for protein, lipid, and carbohydrates.

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