Comparative sperm ultrastructure of three species in Siniperca (Teleostei: Perciformes: Sinipercidae)

Human Sperm Remain Motile After a Temporary Energy Restriction but do Not Undergo Capacitation-Related Events

To acquire fertilization competence, mammalian sperm must undergo several biochemical and physiological modifications known as capacitation. Despite its relevance, the metabolic pathways that regulate the capacitation-related events, including the development of hyperactivated motility, are still poorly described. Previous studies from our group have shown that temporary energy restriction in mouse sperm enhanced hyperactivation, in vitro fertilization, early embryo development and pregnancy rates after embryo transfer, and it improved intracytoplasmic sperm injection results in the bovine model. However, the effects of starvation and energy recovery protocols on human sperm function have not yet been established. In the present work, human sperm were incubated for different periods of time in medium containing glucose, pyruvate and lactate (NUTR) or devoid of nutrients for the starving condition (STRV). Sperm maintained in STRV displayed reduced percentages of motility and kinematic parameters compared to cells incubated in NUTR medium. Moreover, they did not undergo hyperactivation and showed reduced levels of ATP, cAMP and protein tyrosine phosphorylation. Similar to our results with mouse sperm, starvation induced increased intracellular Ca2+ concentrations. Starved human sperm were capable to continue moving for more than 27 h, but the incubation with a mitochondrial uncoupler or inhibitors of oxidative phosphorylation led to a complete motility loss. When exogenous nutrients were added back (sperm energy recovery (SER) treatment), hyperactivated motility was rescued and there was a rise in sperm ATP and cAMP levels in 1 min, with a decrease in intracellular Ca2+ concentration and no changes in sperm protein tyrosine phosphorylation. The finding that human sperm can remain motile for several hours under starvation due to mitochondrial use of endogenous metabolites implies that other metabolic pathways may play a role in sperm energy production. In addition, full recovery of motility and other capacitation parameters of human sperm after SER suggests that this treatment might be used to modulate human sperm fertilizing ability in vitro.

Sperm competition, sexual selection and the diverse reproductive biology of Osteoglossiformes

Osteoglossiformes are an order of "bony tongue" fish considered the most primitive living order of teleosts. This review seeks to consolidate known hypotheses and identify gaps in the literature regarding the adaptive significance of diverse reproductive traits and behaviour of osteoglossiforms within the context of sperm competition and the wider lens of sexual selection. Many of the unusual traits observed in osteoglossiforms indicate low levels of sperm competition; most species have unpaired gonads, and mormyroids are the only known vertebrate species with aflagellate sperm. Several osteoglossiform families have reproductive anatomy associated with internal fertilization but perform external fertilization, which may be representative of the evolutionary transition from external to internal fertilization and putative trade-offs between sperm competition and the environment. They also employ every type of parental care seen in vertebrates. Geographically widespread and basally situated within teleosts, osteoglossiforms present an effective study system for understanding how sperm competition and sexual selection have shaped the evolution of teleost reproductive behaviour, sperm and gonad morphology, fertilization strategies, courtship and paternal care, and sexual conflict. The authors suggest that the patterns seen in osteoglossiform reproduction are a microcosm of teleost reproductive diversity, potentially signifying the genetic plasticity that contributed to the adaptive radiation of teleost fishes.

High-Quality Genome Assembly and Annotation of the Big-Eye Mandarin Fish (Siniperca knerii)

The big-eye mandarin fish (Siniperca knerii) is an endemic species of southern China. It belongs to the family Sinipercidae, which is closely related to the well-known North American sunfish family Centrarchidae. Determining the genome sequence of S. knerii would provide a foundation for better examining its genetic diversity and population history. A novel sequenced genome of the Sinipercidae also would help in comparative study of the Centrarchidae using Siniperca as a reference. Here, we determined the genome sequence of S. knerii using 10x Genomics technology and next-generation sequencing. Paired-end sequencing on a half lane of HiSeq X platform generated 56 Gbp of raw data. Read assembly using Supernova assembler resulted in two haplotype genomes with 732.1 Mb in size and an average GC content of 40.4%, which is consistent with genome size previously reported or estimated using k-mer counting. A total of 7,989 scaffolds with an N50 score of 12.64 Mb were obtained. The longest scaffold was 30.54 Mb. Evaluation of the genome completeness using BUSCO confirmed that 96.5% genes of the Actinopterygii Benchmarking Universal Single-Copy Orthologs were found in the assembled genome of S. knerii Gene prediction using Maker annotation kit resulted in 28,440 genes, of which 25,899 genes had at least one hit comparing to the NCBI Nr database, KEGG or InterProScan5. Pairwise sequentially Markovian coalescent (PSMC) analysis of the genome showed that there was a bottleneck event of the population of S. knerii between 70 ka - 20 ka, which was concordant with the Tali glacier period, suggesting a population decline of S. knerii probably due to climate conditions.

Changes in sperm parameters of sex-reversed female mandarin fish Siniperca chuatsi during cryopreservation process

This works studies the physiological characteristics (sperm motility characteristics) and biochemical characteristics (DNA damage, enzymes activities and fertilization ability) of fresh and freeze-thawed semen of sex-reversed female mandarin fish Siniperca chuatsi (n = 30) obtained with the application of 17α-methyl testosterone for sex reversal. The fresh sperm motility and fertilization rate of sex-reversed females were about 83% and 70% respectively which had no significant difference with normal males (p > 0.05). Except for the value of DNA damage, other values of sperm motility, related enzymes activities and fertilization rate of sex-reversed female sperm declined after a process of cryopreservation (p < 0.05). But the frozen sperm can still get nearly 60% of the fertilization rate. This study identified the physiological and biochemical characteristics of the fresh and cryopreserved sperm from sex-reversed female mandarin fish, and the sex-reversed female spermatozoa can be used for actual production.

Changes in Atlantic salmon (Salmo salar) sperm morphology and membrane lipid composition related to cold storage and cryopreservation

The cold storage and cryopreservation of semen decrease sperm quality. Morphological and biochemical analyses of spermatozoa provide valuable information for the optimization of storage protocols to obtain a sufficient number of spermatozoa for in vitro fertilization. The aim of this study was to evaluate the morphology and lipid composition of Atlantic salmon (Salmo salar) spermatozoa after storage at 4 °C and cryopreservation. Semen samples were obtained by stripping. One aliquot was stored at 4 °C for 7 days, and another aliquot was cryopreserved. The morphology and ultrastructure were analysed using electron microscopy. The lipid composition was analysed by gas chromatography and a commercial kit. After cold storage, the mitochondrion was the most affected component; however, plasma membrane rupture and detachment of the flagellum were also observed. Morphological abnormalities were greater in cryopreserved spermatozoa. The head and mid-piece were dehydrated, sperm membranes were vesiculated, and alterations of mitochondria were observed. After cold storage and cryopreservation, there were less polyunsaturated and omega-3 fatty acids. Furthermore, there was an increase in saturated fatty acids and decrease in cholesterol concentration after cryopreservation (P < 0.05). Based on the results, cryopreservation drastically damaged sperm membranes; the cryogenic damage was associated with membrane lipid composition alterations. The sperm membranes were affected less by cold storage but there was also a decrease of some lipids; therefore, there is a need for improvement in cold storage processes to decrease structural damage of spermatozoa so that semen cryopreservation can be effectively used in the salmon industry.

Morphology and ultrastructure of pink cusk-eel (Genypterus blacodes, Schneider 1801) spermatozoa by scanning and transmission electron microscopy

In this study, the morphology and ultrastructure of Genypterus blacodes spermatozoa were characterized through scanning and transmission electron microscopy. Findings revealed that the G. blacodes spermatozoa can be differentiated into three major parts: a spherical head without an acrosome (typical for externally fertilizing fish), a short mid-piece, and a long flagellum. The mean length of the spermatozoa was 57.6 ± 6.08 μm, with flagella accounting for 56.2 ± 7.2 μm. The head was 1.47 ± 0.2 μm long, and 0.89 ± 0.06 μm wide. The mid-piece had a total dimension of 0.72 ± 0.16 μm, and was 0.31 ± 0.02 μm in length and 0.6 ± 0.05 μm in width. It was located lateral to the nucleus and contained 4 or 5 spherical mitochondria. The mitochondria were separated from the axoneme by a cytoplasmic canal. The main piece of the flagellum had short irregular side-fins, and the axoneme was composed of the typical 9 + 2 microtubular doublet structure enclosed by a cell membrane. The present study reveals that G. blacodes sperm can be categorized as a primitive type. This study is the first to provide comprehensive details on the morphology and ultrastructure of spermatozoa in G. blacodes.

Ultrastructural Studies of Germ Cell Development and the Functions of Leydig Cells and Sertoli Cells associated with Spermatogenesis in Kareius bicoloratus (Teleostei, Pleuronectiformes, Pleuronectidae)

The ultrastructures of germ cells and the functions of Leydig cells and Sertoli cells during spermatogenesis inmale Kareius bicoloratus (Pleuronectidae) were investigated by electron microscope observation. Each of the well-developed Leydig cells during active maturation division and before spermiation contained an ovoid vesicular nucleus, a number of smooth endoplasmic reticula, well-developed tubular or vesicular mitochondrial cristae, and several lipid droplets in the cytoplasm. It is assumed that Leydig cells are typical steroidogenic cells showing cytological characteristics associated with male steroidogenesis. No cyclic structural changes in the Leydig cells were observed through the year. However, although no clear evidence of steroidogenesis or of any transfer of nutrients from the Sertoli cells to spermatogenic cells was observed, cyclic structural changes in the Sertoli cells were observed over the year. During the period of undischarged germ cell degeneration after spermiation, the Sertoli cells evidenced a lysosomal system associated with phagocytic function in the seminiferous lobules. In this study, the Sertoli cells function in phagocytosis and the resorption of products originating from degenerating spermatids and spermatozoa after spermiation. The spermatozoon lacks an acrosome, as have been shown in all teleost fish spermatozoa. The flagellum or sperm tail of this species evidences the typical 9+2 array of microtubules.

Disease resistance and immune-relevant gene expression in golden mandarin fish, Siniperca scherzeri Steindachner, infected with infectious spleen and kidney necrosis virus-like agent

Infectious spleen and kidney necrosis virus (ISKNV), family Iridoviridae, genus Megalocytivirus, may cause high mortality rates such as those seen in mandarin fish, Siniperca chuatsi. ISKNV has attracted much attention due to the possible environmental threat and economic losses it poses on both cultured and wild populations. We have investigated the pathogenicity of ISKNV-like agent Megalocytivirus, isolated from infected pearl gourami, in golden mandarin fish, Siniperca scherzeri - a member of the Percichthyidae family - and in another Percichthyidae species, S. chuatsi. Fish were challenged with four different doses of ISKNV-like agent Megalocytivirus (1, 10, 100 or 1000 μg per fish) over a 30-day period, and cumulative fish mortalities were calculated for each group. No significant mortality was observed for fish challenged with the lowest dose (1 μg per fish) relative to a control group. However, all other challenged groups showed 100% mortality over a 30-day period in proportion to the challenge dose. Quantitative real-time PCR was performed to measure mRNA expression levels for six immune-related genes in golden mandarin fish following ISKNV-like agent challenge. mRNA expression levels for IRF1, Mx, viperin and interleukin 8 significantly increased, while mRNA levels for IRF2 and IRF7 remained constant or declined during the challenge period.