Expression of cathepsin H in differentiating rat spermatids: immunoelectron microscopic study

Cathepsin H: molecular characteristics and clues to function and mechanism

Cathepsin H (CatH) is a lysosomal cysteine protease with a unique aminopeptidase activity that is extensively expressed in the lung, pancreas, thymus, kidney, liver, skin, and brain. Owing to its specific enzymatic activity, CatH has critical effects on the regulation of biological behaviours of cancer cells and pathological processes in brain diseases. Moreover, a neutral pH level is optimal for CatH activity, so it is expected to be active in the extra-lysosomal and extracellular space. In the present review, we describe the expression, maturation, and enzymatic properties of CatH, and summarize the available experimental evidence that mechanistically links CatH to various physiological and pathological processes. Finally, we discuss the challenges and potentials of CatH inhibitors in CatH-induced disease therapy.

The stallion sperm acrosome: Considerations from a research and clinical perspective

During the fertilization process, the interaction between the sperm and the oocyte is mediated by a process known as acrosomal exocytosis (AE). Although the role of the sperm acrosome on fertilization has been studied extensively over the last 70 years, little is known about the molecular mechanisms that govern acrosomal function, particularly in species other than mice or humans. Even though subfertility due to acrosomal dysfunction is less common in large animals than in humans, the evaluation of sperm acrosomal function should be considered not only as a complementary but a routine test when individuals are selected for breeding potential. This certainly holds true for stallions, which might display lower levels of fertility in the face of "acceptable" sperm quality parameters determined by conventional sperm assays. Nowadays, the use of high throughput technologies such as flow cytometry or mass spectrometry-based proteomic analysis is commonplace in the research arena. Such techniques can also be implemented in clinical scenarios of males with "idiopathic" subfertility. The current review focuses on the sperm acrosome, with particular emphasis on the stallion. We aim to describe the physiological events that lead to the acrosome formation within the testis, the role of very specific acrosomal proteins during AE, the methods to study the occurrence of AE under in vitro conditions, and the potential use of molecular biology techniques to discover new markers of acrosomal function and subfertility associated with acrosomal dysfunction in stallions.

Understanding the Underlying Molecular Mechanisms of Meiotic Arrest during In Vitro Spermatogenesis in Rat Prepubertal Testicular Tissue

In vitro spermatogenesis appears to be a promising approach to restore the fertility of childhood cancer survivors. The rat model has proven to be challenging, since germ cell maturation is arrested in organotypic cultures. Here, we report that, despite a meiotic entry, abnormal synaptonemal complexes were found in spermatocytes, and in vitro matured rat prepubertal testicular tissues displayed an immature phenotype. RNA-sequencing analyses highlighted up to 600 differentially expressed genes between in vitro and in vivo conditions, including genes involved in blood-testis barrier (BTB) formation and steroidogenesis. BTB integrity, the expression of two steroidogenic enzymes, and androgen receptors were indeed altered in vitro. Moreover, most of the top 10 predicted upstream regulators of deregulated genes were involved in inflammatory processes or immune cell recruitment. However, none of the three anti-inflammatory molecules tested in this study promoted meiotic progression. By analysing for the first time in vitro matured rat prepubertal testicular tissues at the molecular level, we uncovered the deregulation of several genes and revealed that defective BTB function, altered steroidogenic pathway, and probably inflammation, could be at the origin of meiotic arrest.

Nuage proteins: their localization in subcellular structures of spermatogenic cells as revealed by immunoelectron microscopy

Chromatoid body (CB) was identified as granules stained by basic dye 130 years ago and called by various names. Electron microscopy revealed that the CB belonged to nuage (cloud in French) specific for germ cells. We described the localization of several proteins, including RNA helicases, in the nuage compartments classified into six types and in several spermatogenic cell-specific structures. All the proteins examined were detected in the nuage, including the CB with different staining intensities. Several proteins were localized to non-nuage structures, suggesting that these nuage proteins structures are related to nuage function.

Acrosome biosynthesis in spermatocytes and spermatids revealed by HPA lectin cytochemistry

The origin of the acrosome is controversial, because of both its lysosomal nature and at the moment of its appearance, which seems to be species-specific. Considering the amazing organization shown by the acrosome of some urodele amphibians, HPA-colloidal gold cytochemistry was used to analyze the biogenesis of the acrosome in the urodele Pleurodeles waltl at electron microscopy level. The results showed that HPA-labeling is useful to label the acrosome and its precursor vesicles and, consequently, HPA-histochemistry could be used as a marker of acrosomal content. Labeling of the Golgi apparatus and precursor vesicles was seen in primary spermatocytes and round (stage I) spermatids, thus contributing solid evidence for the beginning of acrosome biogenesis before meiosis. In both primary spermatocytes and round spermatids, an enigmatic vesicle, probably related to the biosynthesis of the neck piece or the tail, was also labeled. Labeling in elongating spermatids (stage II-IV), showed a homogeneous distribution of colloidal gold particles in the acrosomal cap, but the perforatorium was not positive to the lectin. However, in mature (stage V-VI) spermatids, a regional distribution of labeling in the acrosome was seen, with the apical knob showing a stronger labeling than the lateral barb, and the lateral barb showing a stronger labeling than the principal piece of the acrosomal cap. This regional distribution of the labeling suggests that the acrosome develops several domains with different glycoconjugate compositions.

The mammalian acrosome as a secretory lysosome: new and old evidence

The morphological and biochemical characteristics of the acrosome depart well from any other vesicles in somatic cells, making it one of a kind amongst secretory vesicles. The components of the acrosome include a mixture of unique enzymes like acrosin and other enzymes that when present in somatic cells are commonly found in lysosomes, peroxisomes, and even in the cytoplasm. Several observations have pointed out that acrosomal biogenesis has unique features not previously described in secretory vesicle biogenesis of somatic cells. In this review we discuss the evidence supporting a molecular link between the machinery involved in lysosome and acrosome biogenesis, link which may help account for the acrosome unique composition.

Ubiquitin signals in the developing acrosome during spermatogenesis of rat testis: an immunoelectron microscopic study

The localization of ubiquitin (UB) signals in the acrosomes of rat spermiogenic cells was investigated by immunoelectron microscopy using two anti-UB antibodies: UB1, reacting with ubiquitinated proteins and free UB; and FK1, recognizing polyubiquitinated proteins but not monoubiquitinated proteins or free UB. Labeling of UB by UB1 (UB1 signal) was detected in the acrosomes at any stage of differentiation. In step 1 spermatids, UB1 signals were detected on the cytoplasmic surface and in the matrix of transport vesicles located between the trans-Golgi network and the acrosome. Weak signals were detected in acrosomal granules within acrosome vesicles that had not yet attached to the nucleus. In step 4-5 spermatids, the acrosome vesicles had enlarged and attached to the nucleus. Strong gold labeling was noted in a narrow space between the outer acrosomal membrane and the developing acrosomal granule, where a dense fibrous material was observed on routine electron microscopy, whereas the acrosomal granule was weakly stained by UB1 antibody. In step 6-8 spermatids, UB1 signals were detected in the fibrous material that expanded laterally to form a narrow electronless dense zone between the acrosomal granule and the outer acrosomal membrane. Labeling in the acrosomal granule increased. In step 9-11 spermatids, UB1 signals were confined to the narrow zone from the tip of the head to the periphery of the ventral fin. The matrix of the acrosome was weakly stained. In epididymal sperm, UB1 labeling in the acrosome decreased without any pretreatment, whereas staining was noted in a spot in the neck region and in the dorsal fin after trypsin digestion. On the other hand, the staining pattern with FK1 was quite different from that with UB1. The trans-Golgi network was weakly stained but the cis-Golgi network was strongly stained. The dense fibrous material just beneath the outer membrane was never stained with FK1. The results suggest that UB on the surface of transport vesicles is involved in anterograde transport from the Golgi apparatus to the acrosome. The physiological role of UB in acrosomes is not clear. Two candidates for monoubiquitinated proteins in the acrosome, which have a UB-interacting motif, were found by cyber screening.

Innovative techniques and applications in histochemistry and cell biology

Recent studies documenting novel histochemical methods and applications in cell biology and in other areas of the life sciences have again rendered insights into structure and functions of tissues, cells, and cellular components to the level of proteins and genes. Particularly, sophisticated microscopic techniques have proved to be able to significantly advance our knowledge. Findings of recent investigations representing this progress are summarized in the present review.