Rodlet Cells Structure References Rodlet Cell Workshop

Schematic Diagram of Rodlet Cell Structure


A "typical" rodlet cell has a thick capsule around its exterior circumference. Despite the similarity to the cell wall of plants, this capsule is internal to the plasma membrane and probably is a product of the cellular synthesis pathways involving ribosomes and the Golgi apparatus.

Mitochondria are numerous as are profiles of rough endoplasmic reticulum (RER). The most conspicuous feature are the rodlets, whcih consist of a very dense inner core and a less-dense outer "halo" around them. The exact composition of the rodlets is unknown. Various older reports suggested they contained DNA, but this is questionable in light of more modern methods of DNA analysis. They do not stain positive for the common stains for carbohydrates, including the periodic acid/Schiff reaction. The rodlets may be crystallized secretory material, i.e., protein that has precipitated out in a crsytalline for as an inclusion, due to internal conditions of the cell. The rodlets, whatever their nature, are formed by the RER and modified in the Golgi apparatus. They might therefore be regarded as inclusion bodies akin to those formed in bacteria overexpressing insoluble proteins, even though they apparently lack a boundary membrane.

The cell diagrammed here is in the mature state: the rodlets are fully formed and the polarization of the cell is compete: the rodlet tips with exposed cores are directed to the apex, specifically to the point on the capsule where they will emerge when the capsule forms the discharge stigma. It has been suggested that the rodlet cores actually perforate the capsule or at least initiate the process of capsular degradation at this spot, but this has not been convincingly shown to be the case.

Another consistent feature of the polarization of the rodlet cell is the location of the nucleau, which is invariably at the pole opposite to the site of release of the contents.

The capsule is thought to be contractile. To date no published data is available on whether it contains the actin and myosin typical of contractile materials, but morphologically, the expulsion of the contents, including the rodlets, has the characteristics of a forcible process. Intact rodlets are expelled, but they soon are either dissolved or somehow diffuse away from the site of release.

The fate of the capsule and/or the rodlet cell itself is not known. It is unclear whether the rodlet cell is a "one shot" type, and that new rodlet cells are recruited when needed from precursors. The sites of discharged are often associated with the presence of many melanomacrophages, which may engulf and destroy the emptied capsule.

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