Endogenous substrate for energy metabolism and ultrastructural correlates in spermatozoa of the sea urchin Diadema setosum

Comparative studies on the energy metabolism in spermatozoa of four closely related species of sea urchins (genus Echinometra) in Okinawa

Sea urchins of the genus Echinometra are abundant on Okinawa reef flats in southern Japan. The Okinawan Echinometra is designated into four sympatric and closely related species: A, B, C, and D (Ea, Eb, Ec, and Ed). The sperm head size and shape gradually changes to become longer and more slender according to the following order: Ea, Eb, Ec, and Ed. To obtain information regarding speciation in Okinawan Echinometra, this study examined comparatively the energy production system of spermatozoa of Ea, Eb, Ec, and Ed. All spermatozoa contained cholesterol and several kinds of phospholipids. Glycogen, glucose, and triglyceride were present at extremely low levels. After incubation in sea-water, a decrease in the level of phosphatidylcholine (PC) was observed in all spermatozoa concomitantly with activation of motility and respiration. The hydrolysis of PC correlated with the activity of phospholipase A2. Interestingly, the amount of PC consumed, the respiratory rate, and the phospholipase A2 activity in spermatozoa of Ea and Eb were approximately two-fold higher than those of Ec and Ed. Ultrastructural studies showed that lipid bodies within mitochondria were present in the midpieces of all species of spermatozoa. They became small or disappeared after incubation in seawater. Thus, the results obtained strongly suggest that spermatozoa of Ea, Eb, Ec, and Ed all use PC located in the lipid bodies as a substrate for energy metabolism. Also, it seems likely that energy production activities in Ea and Eb spermatozoa are stronger than those in Ec and Ed. The properties of energy metabolism in different species of sea urchin may be related to their habitat.

Ultrastructural study of endogenous energy substrates in spermatozoa of the four species of the sea urchin, Echinometra mataei

The sea urchin Echinometra mathaei (Blainville) which belongs to the order Echinoida, occurs in abundance on shallow reefs throughout the tropical to warm Indo-Pacific region. Though Okinawan E. mathaei had been considered as a single species showing extensive morphological variation in test shape and spine colour, it was recently shown that the genus Echinomtra consists of four independent species (Uehara & Shingaki, 1984, 1985; Arakaki et al., 1998). However, the scientific names of these four complex species found in Okinawa are still unclear. These Echinometra are tentatively described here as Echinometra sp. A, B, C and D. Echinometra sp. A is characterised by white-tipped spines, a definite bright milled ring and dark skin on the peristome. Echinometra sp. B is characterised by spines with no white tip, with very faded milled rings and dark skin on the peristome. Echinometra sp. D is characterised by spines without a white tip but with a definite bright milled ring and bright skin on the peristome. In the field, these two Echinometra sp. exhibit a richly coloured variation in spines. Echinometra sp. D is characterised by deep black spines with well-defined milled rings and dark skin around the peristome. Only black-spined individuals have been found so far. In addition, these species show different distribution patterns, habitat preference and agonistic behaviour. It has also been shown that these two species are not possible to cross-fertilise under sperm at limiting concentration.

The transcriptional and translational control of diazepam binding inhibitor expression in rat male germ-line cells

The diazepam binding inhibitor [DBI, also known as acyl-CoA-binding protein, (ACBP), or endozepine] is a 10-kD protein that has been suggested to be involved in the regulation of several biological processes such as acyl-CoA metabolism, steroidogenesis, insulin secretion, and gamma-aminobutyric acid type A (GABA(A))/benzodiazepine receptor modulation. DBI has been cloned from vertebrates, insects, plants, and yeasts. In mammals, DBI is expressed in almost all the tissues studied. Nevertheless, DBI expression is restricted to specific cell types. Here we have studied DBI gene expression in the germ-line cells of rat testis. The DBI gene was intensively transcribed in postmeiotic round spermatids from stages VI to VIII of the seminiferous epithelial cycle. A prominent, spermatid-specific upstream transcription initiation site was identified in addition to the multiple common transcriptional initiation sites found in the somatic tissues. However, no DBI protein was detected in round spermatids, suggesting that the DBI transcripts were translationally arrested. The DBI protein was detected in the late spermatogenic stages starting from elongating spermatids from step 18 (stage VI) onward. The DBI protein was also detected in mature spermatozoa and in ejaculated human sperms. The majority of DBI was located at the middle piece of the spermatozoons tail enriched with mitochondria. On the basis of this observation and the well-established role of DBI in acyl-CoA metabolism, we propose that DBI expression in spermatozoa reflects the usage of fatty acids as a primary energy source by spermatozoa. The biological function of DBI in spermatozoa could thus be related to the motility function of sperm.