Structural Polarity and Dynamics of Male Germline Stem Cells in an Insect (Milkweed Bug Oncopeltus fasciatus)
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Knowing the structure opens a door for a better understanding of function because there is no function without structure.
Male germline stem cells (GSCs) of the milkweed bug (Oncopeltus fasciatus) exhibit a very extraordinary structure and a very special relationship with their niche, the apical cells. This structural
relationship is strikingly different from that known in the fruit fly (Drosophila melanogaster)—the most successful model system, which allowed deep insights into the signaling interactions between GSCs and niche. The
complex structural polarity of male GSCs in the milkweed bug combined with their astonishing dynamics suggest that cell morphology
and dynamics are causally related with the most important regulatory processes that take place between GSCs and niche and
ensure maintenance, proliferation, and differentiation of GSCs in accordance with the temporal need of mature sperm. The intricate
structure of the GSCs of the milkweed bug (and probably of some other insects, i.e., moths) is only accessible by electron
microscopy. But, studying singular sections through the apical complex (i.e., GSCs and apical cells) is not sufficient to
obtain a full picture of the GSCs; especially, the segregation of projection terminals is not tangible. Only serial sections
and their overlay can establish whether membrane ingrowths merely constrict projections or whether a projection terminal is
completely cut off. To sequence the GSC dynamics, it is necessary to include juvenile stages, when the processes start and
the GSCs occur in small numbers. The fine structural analysis of segregating projection terminals suggests that these terminals
undergo autophagocytosis. Autophagosomes can be labeled by markers. We demonstrated acid phosphatase and thiamine pyrophosphatase
(TPPase). Both together are thought to identify autophagosomes. Using the appropriate substrate of the enzymes and cerium
chloride, the precipitation of electron-dense cerium phosphate granules indicates the presence of enzymes and their location.
Because the granules are very fine, they can be easily assigned to distinct cell organelles as the autophagosomes. Two methods,
electron microscopy and immunocytochemistry, have pointed out a structural polarity and dynamics that are unprecedented for
stem cells. We propose that these dynamics indicate a novel type of signal exchange and transduction between stem cells and
their niche.
Affiliation(s): (3) Laboratory of Developmental Hematopoiesis, Cell Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY, USA
(4) Institute of Zoology, Johannes Gutenberg University, Mainz, Germany
(4) Institute of Zoology, Johannes Gutenberg University, Mainz, Germany
Book Title: Germline Stem Cells
Series: Methods in Molecular Biology | Volume: 450 | Pub. Date: Apr-01-2008 | Page Range: 71-94 | DOI: 10.1007/978-1-60327-214-8_5
Subject: Cell Biology
Key Words: Electron microscopy - GSC dynamics - immunocytochemistry - male GSC - milkweed bug - structural polarity
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