The production of highly specialized spermatozoa from undifferentiated spermatogonia is a strictly organized and programmed process requiring extensive restructuring of the entire cell. One of the most remarkable cellular transformations accompanying the various phases of spermatogenesis is the profound remodelling of the nuclear architecture, in which the nuclear envelope (NE) seems to be crucially involved. In recent years, several proteins from the distinct layers forming the NE (i.e. the inner and outer nuclear membranes as well as the nuclear lamina) have been associated with meiosis and/or spermiogenesis in different mammalian species. Among these are A-and B-type lamins, Dpy-19-like protein 2 (DPY19L2), lamin B receptor (LBR), lamina-associated polypeptide 1 (LAP1), LAP2/emerin/MAN1 (LEM) domain-containing proteins, spermatogenesis-associated 46 (SPATA46) and diverse elements of the linker of nucleoskeleton and cytoskeleton (LINC) complex, namely Sad-1/UNC-84 homology (SUN) and Klarsicht/ANC-1/Syne-1 homology (KASH) domain-containing proteins. Herein, we summarize the current state of the art on the cellular and subcellular distribution of NE proteins expressed during mammalian spermatogenesis, and discuss the latest research developments regarding their testis-specific functions. This review provides a comprehensive and innovative overview of the NE network as a regulatory platform and as an essential determinant of efficient meiotic chromosome recombination as well as spermiogenesis-associated nuclear remodelling and differentiation in mammalian male germline cells. Thus, this review provides important novel insights on the biological relevance of NE proteins for male fertility.

Lamina-associated polypeptide 1 (LAP1) is a type II transmembrane protein of the inner nuclear membrane encoded by the human gene TOR1AIP1. LAP1 is involved in maintaining the nuclear envelope structure and appears be involved in the positioning of lamins and chromatin. To date, LAP1’s precise function has not been fully elucidated but analysis of its interacting proteins will permit unraveling putative associations to specific cellular pathways and cellular processes. By assessing public databases it was possible to identify the LAP1 interactome, and this was curated. In total, 41 interactions were identified. Several functionally relevant proteins, such as TRF2, TERF2IP, RIF1, ATM, MAD2L1 and MAD2L1BP were identified and these support the putative functions proposed for LAP1. Furthermore, by making use of the Ingenuity Pathways Analysis tool and submitting the LAP1 interactors, the top two canonical pathways were “Telomerase signalling” and “Telomere Extension by Telomerase” and the top functions “Cell Morphology”, “Cellular Assembly and Organization” and “DNA Replication, Recombination, and Repair”. Once again, putative LAP1 functions are reinforced but novel functions are emerging.

Spermatogenesis comprises highly complex differentiation processes. Nuclear envelope (NE) proteins have been associated with these processes, including lamins, lamina-associated polypeptide (LAP) 2 and the lamin B-receptor. LAP1 is an important NE protein whose function has not been fully elucidated, but several binding partners allow predicting putative LAP1 functions. To date, LAP1 had not been associated with spermatogenesis. In this study, LAP1 expression and cellular/subcellular localization during spermatogenesis in human and mouse testes is established for the first time. The fact that LAP1 is expressed during nuclear elongation in spermiogenesis and is located at the spermatids’ centriolar pole is singularly important. LAP1 binds to members of the protein phosphatase 1 (PP1) family. Similar localization of LAP1 and PP1γ2, a testis-specific PP1 isoform, suggests a shared function for both proteins during spermiogenesis. Furthermore, this study suggests an involvement of LAP1 in manchette development and chromatin regulation possibly via interaction with acetylated α-tubulin and lamins, respectively. Taken together, the present results indicate that, by moving to the posterior pole in spermatids, LAP1 can contribute to the achievement of non-random, sperm-specific chromatin distribution, as well as modulate cellular remodeling during spermiogenesis. In addition, LAP1 seems to be associated with dynamic microtubule changes related to manchette formation and flagella development.

In medicine, safety and efficacy are the two pillars on which the implementation of novel treatments rest. To protect the patient from unnecessary or unsafe treatments, usually, a stringent path of (pre) clinical testing is followed before a treatment is introduced into routine patient care. However, in reproductive medicine several techniques have been clinically introduced without elaborate preclinical studies. Moreover, novel reproductive techniques may harbor safety risks not only for the patients undergoing treatment, but also for the offspring conceived through these techniques. If preclinical (animal) studies were performed, efficacy and functionality the upper hand. When a new medically assisted reproduction (MAR) treatment was proven effective (i.e. if it resulted in live birth) the treatment was often rapidly implemented in the clinic. For IVF, the first study on the long-term health of IVF children was published a decade after its clinical implementation. In more recent years, prospective follow-up studies have been conducted that provided the opportunity to study the health of large groups of children derived from different reproductive techniques. Although such studies have indicated differences between children conceived through MAR and children conceived naturally, results are often difficult to interpret due to the observational nature of these studies (and the associated risk of confounding factors, e.g. subfertility of the parents), differences in definitions of clinical outcome measures, lack of uniformity in assessment protocols and heterogeneity of the underlying reasons for fertility treatment. With more novel MARs waiting at the horizon, there is a need for a framework on how to assess safety of novel reproductive techniques in a preclinical (animal) setting before they are clinically implemented. In this article, we provide a blueprint for preclinical testing of safety and health of offspring generated by novel MARs using a mouse model involving an array of tests that comprise the entire lifespan. We urge scientists to perform the proposed extensive preclinical tests for novel reproductive techniques with the goal to acquire knowledge on efficacy and the possible health effects of to-be implemented reproductive techniques to safeguard quality of novel MARs.

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BRI2 is a ubiquitously expressed type II transmembrane phosphoprotein. BRI2 undergoes proteolytic processing into secreted fragments and during the maturation process it suffers post-translational modifications. Of particular relevance, BRI2 is a protein phosphatase 1 (PP1) interacting protein, where PP1 is able to dephosphorylate the former. Further, disruption of the BRI2:PP1 complex, using BRI2 PP1 binding motif mutants, leads to increased BRI2 phosphorylation levels. However, the physiological function of BRI2 remains elusive; although findings suggest a role in neurite outgrowth and neuronal differentiation. In the work here presented, BRI2 expression during neuronal development was investigated. This increases during neuronal differentiation and an increase in its proteolytic processing is also evident. To elucidate the importance of BRI2 phosphorylation for both proteolytic processing and neuritogenesis, SH-SY5Y cells were transfected with the BRI2 PP1 binding motif mutant constructs. For the first time, it was possible to show that BRI2 phosphorylation is an important regulatory mechanism for its proteolytic processing and its neuritogenic role. Furthermore, by modulating BRI2 processing using an ADAM10 inhibitor, a dual role for BRI2 in neurite outgrowth is suggested: phosphorylated full-length BRI2 appears to be important for the formation of neuritic processes, and BRI2 NTF promotes neurite elongation. This work significantly contributed to the understanding of the physiological function of BRI2 and its regulation by protein phosphorylation. J. Cell. Biochem. 118: 2752-2763, 2017. © 2017 Wiley Periodicals, Inc.

TorsinA is a member of the AAA+ superfamily of adenosine triphosphatases. These AAA+ proteins have numerous biological functions, including vesicle fusion, cytoskeleton dynamics, intracellular trafficking, protein folding, and degradation as well as organelle biogenesis. Of particular interest is torsinA, which is mainly located in the endoplasmic reticulum (ER) and nuclear envelope (NE). Interestingly, mutations in the TOR1A gene (the gene encoding torsinA) are associated with DYT1 dystonia and with the preferential localization of mutated torsinA at the NE, where it is associated with lamina-associated polypeptide 1. A bioinformatics study of the torsinA interactome revealed reproductive processes to be highly relevant, as proteins in this class were found to interact with the former. Interestingly, the torsin protein family had never been previously described to be associated with the mammalian spermatogenic process. Histological staining of torsinA in human testis tissue revealed a granular cytoplasmic localization in mid- and late spermatocytes. We further sought to understand this newly discovered expression of torsinA in the meiotic phase of human spermatogenesis by studying its specific subcellular distribution. TorsinA is not present in the ER as commonly described. The proposal that torsinA might relocate to the pro-acrosomal vesicles in the Golgi apparatus is discussed.

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