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Differences in chromatin condensation during spermiogenesis in two species of fish with distinct protamines
Abstract:
The sperm cells of Mullus surmuletus (family Mullidae, order Perciformes) and Dicentrarchus labrax (family Percichthyidae, order Perciformes) belong respectively to "type I" and "type II" spermiogenesis categorized by Mattei ('70). The protein content in their sperm nuclei consists of two histone-like proteins (Mullus surmuletus) and one typical protamine (D. labrax). In order to correlate the molecular characteristics of these proteins with their function, we have analyzed the molecules in detail and studied at the ultrastructural level the condensation of chromatin during the spermiogenesis in both species. D. labrax has a true protamine of 34 amino acid residues and its sequence (PR4QASRPVR5TR2STAER5V2R4) contains four arginine clusters. The sperm proteins of M. surmuletus contain 110 and 115 amino acid residues and , by their composition (23-24% Lys, 21-22% Arg, 11-12% Ala), they are similar to protamine-like molecules from sperm of molluscs. During the spermiogenesis of D. Labrax, chromatin condensation progresses from small fibro-granular structures (25 +/- 5 nm in diameter), to larger granules (150 +/- 50 nm diameter). M. surmuletus accumulates 25 +/- 5 nm diameter structures in the basal pole of the nucleus; these structures grow till they reach a diameter of 50 +/- 10 nm and finally go through a process of fusion that changes the condensation of chromatin in sperm nuclei, acquiring a homogeneous aspect. These observations show that during spermiogenesis in the studied types, the last stages of chromatin condensation are dependent on the type of nuclear proteins.
Insights
Sperm nuclear proteins in Mullus surmuletus and Dicentrarchus labrax dictate chromatin condensation during spermiogenesis. Type I (M. surmuletus) uses histone-like proteins, while Type II (D. labrax) uses protamine, influencing final nuclear structure.
Area of Science:
- Molecular Biology
- Cell Biology
- Reproductive Biology
Background:
- Spermiogenesis, the process of sperm cell development, involves significant chromatin condensation.
- Different species exhibit distinct types of spermiogenesis (Type I and Type II) characterized by unique nuclear protein compositions.
- Mullus surmuletus (Type I) possesses histone-like proteins, whereas Dicentrarchus labrax (Type II) has a typical protamine.
Purpose of the Study:
- To correlate the molecular characteristics of sperm nuclear proteins with their function in chromatin condensation.
- To investigate the ultrastructural changes during spermiogenesis in M. surmuletus and D. labrax.
Main Methods:
- Analysis of sperm nuclear protein composition and sequence.
- Ultrastructural study of chromatin condensation during spermiogenesis.
- Comparison of protein content and chromatin structure between M. surmuletus and D. labrax.
Main Results:
- D. labrax utilizes a 34-amino acid protamine with arginine clusters.
- M. surmuletus employs larger histone-like proteins (110-115 amino acids) rich in lysine, arginine, and alanine, resembling mollusc protamine-like molecules.
- Chromatin condensation in D. labrax progresses from small to large granules, while M. surmuletus shows accumulation, growth, and fusion of structures, resulting in a homogeneous nucleus.
Conclusions:
- The type of nuclear proteins (histone-like vs. protamine) directly influences the final stages of chromatin condensation during spermiogenesis.
- Distinct spermiogenesis pathways lead to species-specific chromatin organization in sperm nuclei.