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New types of islet cells in a cyclostome, Petromyzon marinus L
Abstract:
Four types of acidophilic granular cells, in addition to B-cells, are identified in the islet organ of anadromous specimens of two subspecies of Petromyzon marinus by light and electron microscopy. Three of these acidophils (PI, PII and PIV-cells) occur in both the cranial and hepatic islets while a fourth type (PIII-cell) has only been found in the hepatic islet of some animals. The granules of the PI-cells stain with ponceau de xylidine, give a distinct tryptophan reaction and in ultrastructural examination show large, dense granules. The PII-cells contain unusual crystals and appear to be a non-secretory stage of the PI. The PIII-cells stain deep-red and acid fuchsin. They contain very large, dense granules and some lysosomes. PIV-cells stain selectively with phosphotungstic acid-hematoxylin and ultrastructurally, contain small, more or less dense granules. It appears that PI- and PIV-cells develop directly from B-cells, while the PIII-cells derive from PI-cells. despite their direct or indirect origin from B-cells, the PI-, PIII- and PIV-cells show characteristic features of functionally independent endocrine cells. Petromyzon marinus may be an ideal model for the understanding of phylogenetic and pathological interrelationships between islet and gastrointestinal hormones. It is clear that the interpretation of the islet organ of the cyclostomes, which has been generally considered a source of insulin only, requires a revaluation.
Insights
The study identifies four new acidophilic granular cell types in the Petromyzon marinus islet organ, distinct from B-cells. These cells suggest a more complex endocrine function beyond insulin in cyclostomes.
Area of Science:
- Comparative endocrinology
- Ichthyology
- Cell biology
Background:
- The islet organ of cyclostomes, including Petromyzon marinus (sea lamprey), has been traditionally viewed as primarily producing insulin.
- Limited understanding exists regarding the diversity and function of endocrine cells within the cyclostome islet organ.
Purpose of the Study:
- To characterize the different types of acidophilic granular cells in the islet organ of anadromous Petromyzon marinus.
- To investigate the origin and potential functional independence of these newly identified cell types.
- To re-evaluate the endocrine function of the cyclostome islet organ.
Main Methods:
- Light microscopy and electron microscopy were employed to examine the islet organ of Petromyzon marinus.
- Histochemical staining techniques (e.g., ponceau de xylidine, acid fuchsin, phosphotungstic acid-hematoxylin) were used to differentiate cell types.
- Ultrastructural analysis was performed to examine granule morphology and cellular components.
Main Results:
- Four distinct types of acidophilic granular cells (PI, PII, PIII, PIV) were identified alongside B-cells in the islet organ.
- PI, PII, and PIV cells were found in both cranial and hepatic islets, while PIII cells were restricted to the hepatic islet.
- PI and PIV cells appear to originate from B-cells, and PIII cells from PI cells, with all exhibiting characteristics of independent endocrine function.
Conclusions:
- The Petromyzon marinus islet organ harbors a greater diversity of endocrine cells than previously recognized, challenging the sole insulin-secreting model.
- These findings highlight Petromyzon marinus as a valuable model for studying the evolution and pathology of islet and gastrointestinal hormones.
- A re-evaluation of the cyclostome islet organ's function is necessary, considering the potential roles of these newly identified cell types.