Mutagenic and genotoxic activities of certain organophosphorus compounds, using Ames Salmonella assay, with and without microsomal induction.
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Animals↗
Biomedical subjects
K Jamil
Publications and source records attributed to K Jamil.
Decondensation of human spermatozoal chromatin by nuclear actin polymerization.
A critical relationship exists between nuclear actin polymerization and decondensation of sperm chromatin. Characteristic decondensation phenomena were brought about by the protein S-1 of heavy meromyosin of rabbit skeletal muscle in sperm that had undergone the acrosome reaction. Sperm treated with only calcium or only ionophore were not affected by the S-1 trigger, and the nucleus remained in the condensed state. Since S-1 specifically binds to actin, it was possible to demonstrate this phenomenon at the ultrastructural level. Maybe there are switches that operate at different steps for events leading to syngamy and fertilization. No switch can be operative until the preceding event has prepared the sperm for entering the next phase. The operations are performed in a perfect sequential order. This investigation leads to the conclusion that decondensation of sperm chromatin is brought about by nuclear actin polymerization.
Acrosome↗
Plasma membrane cytoskeletal complex of the mammalian spermatozoa.
Human and ram sperm were incubated in vitro in Tris buffer with (1) calcium ions, (2) ionophore A23187, (3) calcium plus A23187, (4) without any substance, as described in [13], and were reincubated in situ with the protein S-1 of heavy meromyosin (1 mg/ml). These spermatozoa were examined with the electron microscope to study and characterize the cytoskeletal structures after negative staining, freeze fracturing, and thin sectioning. The formation of the cytoskeletal complex, associated with the plasma membrane in the postacrosome region, appeared to be triggered by S-1 in those sperm that were earlier treated with the ionophore. The dynamic nature of actin present in the postacrosomal dense matrix becomes evident with the formation of a cytoskeletal basket in that region. The cytoskeletal complex may play an important role during the exocytotic acrosome reaction, helping to retain the shape of the sperm head and protect the genetic material until fertilization.
Acrosome↗
Calcium ionophore A23187 as a probe for freeze-fracture studies of membrane changes in the head of human spermatozoa.
The membranes of the head of human spermatozoa were examined after incubating the sperm with and without inophore A23187 and calcium ions, using freeze-fracture electron microscopy. After exposure to ionophore and calcium there was a remarkable rearrangement of the intramembraneous particles, especially in the plasma membrane. Buckling of the plasma membrane occurred prior to breaking away from the outer region of the sperm head. The outer acrosomal membrane bubbled and broke down to form vesicles, and blebbing of the inner acrosome membrane also occurred. The nuclear envelope degenerated and often displayed an undulating topography.
Acrosome↗
Ultrastructural studies of the nuclear envelope in human sperm.
In freeze fracture preparations of normal human spermatozoa, nuclear pores were revealed in hexagonal arrangement over the sperm nucleus. The pores were 85 nm in diameter and were studded with numerous particles. The membrane of normal spermatozoa incubated without ionophore or calcium ions appeared continuous and enclosed the condensed chromatin closely. When the sperm were incubated with ionophore A23187 plus calcium ions to induce the acrosome reaction the nuclear envelope appeared to undergo dramatic topographical and morphological changes. Stretching, expanding, and loosening of the nuclear envelope and breaking down in certain regions was seen in thin sections. The importance of this phenomenon is discussed in relation to similar events occurring when the sperm penetrate the ovum.
Acrosome↗
Induction of acrosomal reaction in sperm with ionophore A23187 and calcium.
The acrosome reaction was induced in ram, rabbit, and human sperm by incubating with the ionophore A23187 plus calcium ions, although the percentage of reacted sperm was different for each species: 90% in ram, 38% in rabbit, and 69% in man. Fusion of the outer acrosomal and plasma membranes of ram and rabbit sperm formed vesicles, but in human sperm only the outer acrosomal membrane was involved in vesiculation. Acrosin was lost from ram, rabbit, and human sperm after treatment with ionophore plus calcium. Ionophore alone induced the reaction in only 35% of ram sperm, 20% of human sperm, and 12% of rabbit sperm. On exposure to A23187 alone, the acrosome of unreacted rabbit sperm bulged and the acrosome and nuclear membrane of human sperm were often lifted away from the nucleus. The percentage of mammalian sperm undergoing the acrosome reaction in the presence of calcium alone, was very low.
Acrosin↗