Differences in chromatin condensation during spermiogenesis in two species of fish with distinct protamines.
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.
Saperas
N
N
Institut de Ciències del MAR, CSIC, Barcelona (N.S.), Spain.
Ribes
E
E
Buesa
C
C
García-Hegart
F
F
Chiva
M
M
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002843:Chromatin / Q000502:physiology* / Q000648:ultrastructure; D008297:Male; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000502:physiology*; D010473:Perciformes; D011479:Protamines / Q000737:chemistry; D013091:Spermatogenesis / Q000502:physiology*; D013094:Spermatozoa / Q000648:ultrastructure
D000596:Amino Acids; D002843:Chromatin; D009687:Nuclear Proteins; D011479:Protamines