Comparative genomics reveals gene-specific and shared regulatory sequences in the spermatid-expressed mammalian Odf1, Prm1, Prm2, Tnp1, and Tnp2 genes

Circadian desynchrony disturbs the function of rat spermatozoa

Decreased male fertility is a growing health problem that requires a better understanding of molecular events regulating reproductive competence. Here the effects of circadian desynchrony on the rat spermatozoa functionality were studied. Circadian desynchrony was induced in rats that lived for 2 months under disturbed light conditions designed to mimic shiftwork in humans (two days of constant light, two days of continual dark, and three days of 14:10 h light:dark schedule). Such a condition abolished circadian oscillations in the rats' voluntary activity, followed by a flattened transcriptional pattern of the pituitary gene encoding follicle stimulating hormone subunit (Fshb), and genes important for germ cell maturation (Tnp1 and Prm2) as well as the clock in seminiferous tubules. However, the number of spermatozoa isolated from the epididymis of the rats suffering from circadian desynchrony did not deviate from the controls. Nevertheless, spermatozoa functionality, estimated by motility and progesterone-induced acrosome reaction, was reduced compared to the control. These changes were associated with the altered level of main markers of mitochondrial biogenesis (Pprgc1a/PGC1A, Nrf1/NRF1, Tfam, Cytc), decreased mitochondrial DNA copy number, ATP content, and clock genes (Bmal1/BMAL1, Clock, Cry1/2, and Reverba). The principal-component-analysis (PCA) points to a positive association of the clock and mitochondrial biogenesis-related genes in spermatozoa from rats suffering circadian desynchrony. Altogether, the results show the harmful effect of circadian desynchrony on spermatozoa functionality, targeting energetic homeostasis.

A 22-amino-acid peptide regulates tight junctions through occludin and cell apoptosis

Occludin is a structural protein of tight junctions (TJ) in the blood–testis barrier (BTB). A 22-amino-acid peptide (22AA) in the second extracellular loop can reversibly regulate TJ, but its regulatory mechanism is unknown. In this study, a 22AA-induced TJ destruction animal model was constructed to investigate the effect of 22AA on Sertoli cells (SCs) and spermatid counts and cell apoptosis at different time points using a multiplex immunofluorescence technique. The effect of 22AA on the location and distribution of occludin was analyzed via dual confocal fluorescence microscope. Western blotting was used to analyze dynamic changes in occludin expression. Real-time RT-PCR was used to analyze miR-122-5p expression changes. Sperm density counts and mating methods were used to analyze the effect of 22AA on fertility in mice. The results showed that 22AA promoted SC and spermatid apoptosis, downregulated occludin, upregulated miR-122-5p, and decreased sperm density and litter size before 27 days (27D). After 27D, the expression of occludin increased again, miR-122-5p expression decreased again, both sperm density and litter size returned to normal, apoptosis stopped, and spermatogenesis began to recover. Therefore, it can be concluded that 22AA can destroy TJ by downregulating occludin and inducing cell apoptosis. After 27D, TJ and spermatogenesis functions return to normal.

Position-dependent interactions of Y-box protein 2 (YBX2) with mRNA enable mRNA storage in round spermatids by repressing mRNA translation and blocking translation-dependent mRNA decay

Many mRNAs encoding proteins needed for the construction of the specialized organelles of spermatozoa are stored as translationally repressed, free messenger ribonucleoproteins in round spermatids, to be actively translated in elongating and elongated spermatids. The factors that repress translation in round spermatids, however, have been elusive. Two lines of evidence implicate the highly abundant and well-known translational repressor, Y-box protein 2 (YBX2), as a critical factor: First, protamine 1 (Prm1) and sperm-mitochondria cysteine-rich protein (Smcp) mRNAs are prematurely recruited onto polysomes in Ybx2-knockout mouse round spermatids. Second, mutations in 3' untranslated region (3'UTR) cis-elements that abrogate YBX2 binding activate translation of Prm1 and Smcp mRNAs in round spermatids of transgenic mice. The abundance of YBX2 and its affinity for variable sequences, however, raise questions of how YBX2 targets specific mRNAs for repression. Mutations to the Prm1 and Smcp mRNAs in transgenic mice reveal that strong repression in round spermatids requires YBX2 binding sites located near the 3' ends of their 3'UTRs as locating the same sites in upstream positions produce negligible repression. This location-dependence implies that the assembly of repressive complexes is nucleated by adjacent cis-elements that enable cooperative interactions of YBX2 with co-factors. The available data suggest that, in vertebrates, YBX2 has the important role of coordinating the storage of translationally repressed mRNAs in round spermatids by inhibiting translational activity and the degradation of transcripts via translation-dependent deadenylation. These insights should facilitiate future experiments designed to unravel how YBX2 targets mRNAs for repression in round spermatids and how mutations in the YBX2 gene cause infertility in humans. Mol. Reprod. Dev. 83: 190-207, 2016. © 2016 Wiley Periodicals, Inc.

The conserved histone deacetylase Rpd3 and its DNA binding subunit Ume6 control dynamic transcript architecture during mitotic growth and meiotic development

It was recently reported that the sizes of many mRNAs change when budding yeast cells exit mitosis and enter the meiotic differentiation pathway. These differences were attributed to length variations of their untranslated regions. The function of UTRs in protein translation is well established. However, the mechanism controlling the expression of distinct transcript isoforms during mitotic growth and meiotic development is unknown. In this study, we order developmentally regulated transcript isoforms according to their expression at specific stages during meiosis and gametogenesis, as compared to vegetative growth and starvation. We employ regulatory motif prediction, in vivo protein-DNA binding assays, genetic analyses and monitoring of epigenetic amino acid modification patterns to identify a novel role for Rpd3 and Ume6, two components of a histone deacetylase complex already known to repress early meiosis-specific genes in dividing cells, in mitotic repression of meiosis-specific transcript isoforms. Our findings classify developmental stage-specific early, middle and late meiotic transcript isoforms, and they point to a novel HDAC-dependent control mechanism for flexible transcript architecture during cell growth and differentiation. Since Rpd3 is highly conserved and ubiquitously expressed in many tissues, our results are likely relevant for development and disease in higher eukaryotes.

Sexual selection on protamine and transition nuclear protein expression in mouse species

Post-copulatory sexual selection in the form of sperm competition is known to influence the evolution of male reproductive proteins in mammals. The relationship between sperm competition and regulatory evolution, however, remains to be explored. Protamines and transition nuclear proteins are involved in the condensation of sperm chromatin and are expected to affect the shape of the sperm head. A hydrodynamically efficient head allows for fast swimming velocity and, therefore, more competitive sperm. Previous comparative studies in rodents have documented a significant association between the level of sperm competition (as measured by relative testes mass) and DNA sequence evolution in both the coding and promoter sequences of protamine 2. Here, we investigate the influence of sexual selection on protamine and transition nuclear protein mRNA expression in the testes of eight mouse species that differ widely in levels of sperm competition. We also examined the relationship between relative gene expression levels and sperm head shape, assessed using geometric morphometrics. We found that species with higher levels of sperm competition express less protamine 2 in relation to protamine 1 and transition nuclear proteins. Moreover, there was a significant association between relative protamine 2 expression and sperm head shape. Reduction in the relative abundance of protamine 2 may increase the competitive ability of sperm in mice, possibly by affecting sperm head shape. Changes in gene regulatory sequences thus seem to be the basis of the evolutionary response to sexual selection in these proteins.

Transcriptome profiling of the developing postnatal mouse testis using next-generation sequencing

Mammalian testis development is a complex and highly sophisticated process. To study the dynamic change of normal testis development at the transcriptional level, we investigated mouse testes at three postnatal ages: 6 days postnatal, 4 weeks old, and 10 weeks old, representing infant (PN1), juvenile (PN2), and adult (PN3) stages, respectively. Using ultra high-throughput RNA sequencing (RNA-seq) technology, we obtained 211 million reads with a length of 35 bp. We identified 18837 genes that were expressed in mouse testes, and found that genes expressed at the highest level were involved in spermatogenesis. The gene expression pattern in PN1 was distinct from that in PN2 and PN3, which indicates that spermatogenesis has commenced in PN2. We analyzed a large number of genes related to spermatogenesis and somatic development of the testis, which play important roles at different developmental stages. We also found that the MAPK, Hedgehog, and Wnt signaling pathways were significantly involved at different developmental stages. These findings further our understanding of the molecular mechanisms that regulate testis development. Our study also demonstrates significant advantages of RNA-seq technology for studying transcriptome during development.

Identification of elements in the Smcp 5' and 3' UTR that repress translation and promote the formation of heavy inactive mRNPs in spermatids by analysis of mutations in transgenic mice

The sperm mitochondria-associated cysteine-rich protein (Smcp) mRNA is transcribed in step 3 spermatids, and is stored in free mRNPs until translation begins ∼6 days later in step 11. To identify sequences that control the timing of Smcp mRNA translation, mutations in both UTRs were analyzed in transgenic mice using green fluorescent protein (GFP), squashes of seminiferous tubules, and quantification of polysomal loading in adult and 21 dpp testes in sucrose and Nycodenz gradients. GFP fluorescence is first detected in step 9 spermatids in lines harboring a transgene containing the Gfp 5' UTR and Smcp 3' UTR. Unexpectedly, this mRNA is stored in large, inactive mRNPs in early spermatids that sediment with polysomes in sucrose gradients, but equilibrate with the density of free mRNPs in Nycodenz gradients. Randomization of the segment 6-38 nt upstream of the first Smcp poly(A) signal results in early detection of GFP, a small increase in polysomal loading in 21 dpp testis, inactivation of the formation of heavy mRNPs, and loss of binding of a Y-box protein. GFP is first detected in step 5 spermatids in a transgene containing the Smcp 5' UTR and Gfp 3' UTR. Mutations in the start codons in the upstream reading frames eliminate translational delay by the Smcp 5' UTR. Collectively, these findings demonstrate that Smcp mRNA translation is regulated by multiple elements in the 5' UTR and 3' UTR. In addition, differences in regulation between Smcp-Gfp mRNAs containing one Smcp UTR and the natural Smcp mRNA suggest that interactions between the Smcp 5' UTR and 3' UTR may be required for regulation of the Smcp mRNA.