Proteome profiling of the sperm maturation milieu in the rhesus monkey (Macaca mulatta) epididymis

The mammalian spermatozoon acquires its fertilising potential during transit through the epididymis, where it interacts with epididymal luminal fluid proteins (the sperm maturation milieu). In order to highlight the epididymal-specific function of the rhesus monkey (Macaca mulatta) in sperm maturation, two-dimensional gel electrophoresis of epididymal luminal fluid proteins was followed by identification by Matrix-Assisted Laser Desorption/ Ionization Time of Flight Mass Spectrometry (MALDI-TOF/MS) or MALDI-TOF/TOF and revealed over five hundred spots, comprising 198 non-redundant proteins. Some mass spectrometric data were confirmed by western blotting identification. Some common epididymal fluid proteins were identified, such as clusterin, α-1-antitrypsin, malate dehydrogenase, L-lactate dehydrogenase B, α-1-acid glycoprotein 1 and α-mannosidase. More than 7% of all proteins were anti-oxidative, which might control oxidative stress within the male tract. When compared with bull and human epididymal luminal fluid proteins, those in the rhesus monkey had more overlap with the human, which provides evidence of a close evolutionary relationship between the rhesus monkey and man. This study provides new proteomic information on possible rhesus monkey epididymal functions and novel potential biomarkers for the noninvasive assessment of male fertility.

Sperm RNA as a Mediator of Genomic Plasticity

Sperm RNA has been linked recently to trans-generational, non-Mendelian patterns of inheritance. Originally dismissed as “residual” to spermatogenesis, some sperm RNA may have postfertilization functions including the transmission of acquired characteristics. Sperm RNA may help explain how trans-generational effects are transmitted and it may also have implications for assisted reproductive technologies (ART) where sperm are subjected to considerable, ex vivo manual handling. The presence of sperm RNA was originally a controversial topic because nuclear gene expression is switched off in the mature mammalian spermatozoon. With the recent application of next generation sequencing (NGS), an unexpectedly rich and complex repertoire of RNAs has been revealed in the sperm of several species that makes its residual presence counterintuitive. What follows is a personal survey of the science behind our understanding of sperm RNA and its functional significance based on experimental observations from my laboratory as well as many others who have contributed to the field over the years and are continuing to contribute today. The narrative begins with a historical perspective and ends with some educated speculation on where research into sperm RNA is likely to lead us in the next 10 years or so.

7UTILIZATION OF CELL PROFILING TO EVALUATE BOVINE SPERMATOZOA IN NORMAL AND SIMULATED MICROGRAVITY

We developed a method to evaluate bovine sperm membranes in normal (1G) and simulated microgravity (Sim-μG). Bovine spermatozoa are used as a model system because they have cellular membranes analogous to those of other cell types, and yet are much simpler because they have no cytoplasm and do not participate in DNA transcription or mRNA translation. They can be cultured as single cells and are easily evaluated for membrane characteristics using flow cytometry. These features make the mammalian spermatozoon a useful model for exploring the principles of membrane structure/function in the presence of a variety of environmental challenges such as simulated microgravity. Cryopreserved, washed beef bull sperm (4–8×106mL−1)were incubated under non-capacitating conditions (modified glucose-free Tyrode’s medium containing low bicarbonate, HEPES buffer, pyruvate and 3mgmL−1 BSA V; 23°C in air), and these spermatozoa remained alive for 24–48h at 1G. To simulate μG, spermatozoa were incubated under the same conditions, in a HARV 10 rotating wall vessel (RWV, Synthecon, Inc, Houston, TX, USA) at 9rpms. Spermatozoa were incubated in 1G and Sim-μG environments for 2.5–4.5h and subsequently exposed to 0, 60 or 80μgmL−1 LC for 0, 4, 8, 12, 16 and 20min. Three fluorochrome combinations were used as probes at each [LC]/time point: (1) propidium Iodide (dead status)+SYBR 14 (live status); (2) PI+FITC-PSA (acrosome reactions [ARs]); (3) PI+MitoTracker Deep Red (mitochondrial activity). Approximately 1million spermatozoa from 3 bulls were evaluated over 4 days. Data were acquired on a FACSVantage SE flow cytometer, and initially analyzed (quality control) using the bundled FACSVantage SE software package (Cell Quest, BD BioSciences, San Jose, CA, USA). This provided graphics of simple cell relations (fluorescence v. LC exposure time). For further statistical analysis, and incorporation of non-parametric statistical tools (including pattern recognition using Support Vector Machines), the data were processed using a collection of Perl scripts and C programs. Results: Live/dead status: When Sim-μG+60μgmL−1 LC sperm were compared to 1G+60μgmL−1LC, and 80μgmL−1 LC sperm, their profiles were more similar to the 1G 80μgmL−1 LC profiles. AR status: the Sim-μG+60μgmL−1 LC profiles were similar to the 1G+60μgmL−1 LC profiles. Mitochondrial Status: the Sim-μG+60μgmL−1LC profiles were more similar to 1G+80μgmL−1 LC profiles. Summary: although Sim-μG sperm lost their motility within 3h, they were alive. Cell profiles indicate that Sim-μG sperm nuclear membranes are less stable and their mitochondria are less functional than the 1G controls, but their acrosomes are intact indicating that fertilizing potential may remain. Additional experiments are needed to determine the time course for Sim-μG, induced changes, and whether Sim-μG sperm can penetrate eggs. Funding: NASA (2002)-Stennis-24 and The University of New Orleans.

Evolution of the Spermatozoon in Australasian Rodents

The head of the spermatozoon in eutherian mammals contains a nucleus, acrosomal cap and cytoskeleton. It is generally spatulate, paddle-shaped or pear-shaped, but in most murid rodents it is hook-shaped with the anterior region of the nucleus surrounded by an elaborate acrosome and an extension of the subacrosomal cytoskeleton as a perforatorium. This type of spermatozoon is present in Australasian Rattus, together with several other New Guinean genera. However, in most Australasian hydromyine rodents a far greater complexity of structural organisation of the sperm head has evolved in which two further elaborate processes extend from its upper concave surface. These processes contain a huge extension of the cytoskeleton within which filamentous actin is present. By contrast, the form of the sperm head in a few species of Pseudomys, Notomys and Solomys is highly divergent and is either truncated, spatulate or pear- shaped. The evolutionary trends of change in sperm head shape are discussed and it is suggested that the falciform sperm head with the two extra processes in most of the hydromyine rodents is one of the most morphologically complex sperm head types to have evolved in eutherian mammals; it contains a far more extensive development of the cytoskeleton than that of any other mammalian spermatozoon.