Spermiogenesis and biflagellate spermatozoon of the teleost fish Lampanyctus crocodilus (Myctophiformes, Myctophidae): ultrastructure and characterisation of its sperm basic nuclear proteins.

We undertook an ultrastructural study of the spermiogenesis of the lanternfish Lampanyctus crocodilus (Myctophiformes, Myctophidae) with special emphasis on the condensation of chromatin and the biochemical characterisation of its sperm nuclear basic proteins (SNBPs). The round head of the early spermatid of L. crocodilus develops into a curved conical-shaped head in the spermatozoon. Two flagella, present even in the spermatid, are inserted laterally at the convex side of the sperm head. Both flagella possess an axoneme with a 9 + 0 instead of the typical 9 + 2 axonemal structure. Mitochondria undergo a characteristic redistribution during spermiogenesis. A reduced number of them are present lying away from the centrioles at both ends of the concave side of the sperm head. During the chromatin condensation stages in spermiogenesis, fibrogranular structures with granules of 25 ± 5 and 50 ± 5 nm can be observed in the early spermatid and develop into larger granules of about 150 ± 50 nm in the middle spermatid. The latter granules coalesce during the transition to the advanced spermatid and spermatozoon giving rise to highly condensed chromatin in the sperm cell. Protamines are the main SNBPs associated with this chromatin; however, they are unusually large and correspond to the largest protamines described in fish to date. Small stoichiometric amounts of histones and other basic proteins coexist with these protamines in the spermatozoon.

First record of the Atlantic bumper Chloroscombrus chrysurus (Teleostei: Carangidae) in the Mediterranean Sea.

In December 1997, one specimen of the Atlantic bumper, Chloroscombrus chrysurus was recorded for the first time in the Mediterranean Sea, off Almuñécar (Granada, Spain: 36° 43' 26″ N; 3° 41' 39″ W). This species probably entered the Mediterranean Sea via the Strait of Gibraltar.

Primary structure of scombrine alpha: two different species with an identical protamine.

We have studied the protamine scombrine alpha from the mackerel Scomber scombrus. Scombrine alpha is found phosphorylated in spermatid nuclei, but not in nuclei of ripe sperm. It is a typical fish protamine, made up of two distinct molecular species, each of 34 amino acid residues. The primary structure of the main component of scombrine alpha is 100% identical to scombrine gamma, the nonmicroheterogeneous protamine from Scomber australasicus (11). The second component of scombrine alpha is a very minor molecular species that has an isoleucine instead of a valine in position 11. Nuclear sperm-specific basic proteins display an enormous interspecific variability and it is very surprising that two different species show identical protamines. In this work we suggest that evolutionary changes in primary structure of protamines are restricted by several constitutive factors, especially when protamines either lack or have a low degree of microheterogeneity.

On the evolution of protamines in bony fish: alternatives to the "retroviral horizontal transmission" hypothesis.

Fish protamines are highly specialized molecules which are responsible for chromatin condensation during the last stages of spermatogenesis (spermiogenesis). However, not all fish contain protamines in their sperm nuclei; rather, there seems to be a random distribution of protamines within this group. The origin of this sporadic presence of protamines in the sperm and its significance have not yet been precisely determined. In this paper we have conducted an exhaustive survey of the literature available on the different types of nuclear protein composition of the sperm of teleost fish in order to try to correlate these data with what is presently known about the taxonomy of this group. The results of this analysis have allowed us to make the following observations. The divergence between protamines and histones has occurred several times during the evolution of the bony fish. However, the relative frequency of this divergence is almost negligible during the differentiation of genera and species (intrafamily variation) and is very small during the differentiation of families (interfamily variation). Nevertheless, the divergence is very noticeable among the different orders. It is therefore possible to conclude from all this that the sporadic distribution of protamines in bony fish is not a random event as initially believed. Furthermore, such a heterogeneous distribution of protamines cannot be easily accounted for by a mechanism of horizontal retroviral transmission through repeated and independent acquisition of a protamine gene as has been recently proposed (Jankowski, Stater, Dixon (1986) J Mol Evol 23:1-10). Rather, it could possibly be explained by a repeated and independent loss of the expression of the protamine gene (or loss of the gene itself) which mainly occurred during the diversification of the orders of this group.