Mammalian egg coat modifications and the block to polyspermy

Fertilization by more than one sperm causes polyploidy, a condition that is generally lethal to the embryo in the majority of animal species. To prevent this occurrence, eggs have developed a series of mechanisms that block polyspermy at the level of the plasma membrane or their extracellular coat. In this review, we first introduce the mammalian egg coat, the zona pellucida (ZP), and summarize what is currently known about its composition, structure, and biological functions. We then describe how this specialized extracellular matrix is modified by the contents of cortical granules (CG), secretory organelles that are exocytosed by the egg after gamete fusion. This process releases proteases, glycosidases, lectins and zinc onto the ZP, resulting in a series of changes in the properties of the egg coat that are collectively referred to as hardening. By drawing parallels with comparable modifications of the vitelline envelope of nonmammalian eggs, we discuss how CG‐dependent modifications of the ZP are thought to contribute to the block to polyspermy. Moreover, we argue for the importance of obtaining more information on the architecture of the ZP, as well as systematically investigating the many facets of ZP hardening.     

The ZP domain is a conserved module for polymerization of extracellular proteins

Many eukaryotic extracellular proteins share a sequence of unknown function, called the zona pellucida (ZP) domain. Among these proteins are the mammalian sperm receptors ZP2 and ZP3, non-mammalian egg coat proteins, Tamm-Horsfall protein (THP), glycoprotein-2 (GP-2), alpha- and beta-tectorins, transforming growth factor (TGF)-beta receptor III and endoglin, DMBT-1 (deleted in malignant brain tumour-1), NompA (no-mechanoreceptor-potential-A), Dumpy and cuticlin-1 (refs 1,2). Here, we report that the ZP domain of ZP2, ZP3 and THP is responsible for polymerization of these proteins into filaments of similar supramolecular structure. Most ZP domain proteins are synthesized as precursors with carboxy-terminal transmembrane domains or glycosyl phosphatidylinositol (GPI) anchors. Our results demonstrate that the C-terminal transmembrane domain and short cytoplasmic tail of ZP2 and ZP3 are not required for secretion, but are essential for assembly. Finally, we suggest a molecular basis for dominant human hearing disorders caused by point mutations within the ZP domain of alpha-tectorin.     

Male reproductive health statement (XIIIth international symposium on Spermatology,may 9th–12th 2018, Stockholm,Sweden

On the occasion of the XIIIth International Symposium on Spermatology held from 9 to 13 May 2018 in Stockholm (Sweden), participants (guest speakers and audience) collectively felt the need to make a public statement on the general issue of male reproductive health. Our intention is to raise awareness of what we believe is a neglected area of research despite alarming situations around the world. The disclosure strategy desired by the co-authors is to bring it to the attention of the greatest number partly by considering co-publication in the various periodicals dealing with Reproductive Biology and Andrology. BaCA’s editorial office accepted this mission and found it natural that our periodical, the official journal of the French Andrology Society (SALF), should carry this message.     

Peridinin-Chlorophyll a-Protein Is not Implicated in the Photosynthesis Rhythm of the Dinoflagellate Gonyaulax despite Circadian Regulation of its Translation

The levels of peridinin-chlorophyll a -protein (PCP) mRNA, apoprotein and protein bound with peridinin (holoprotein) were measured as a function of circadian time in the dinoflagellate Gonyaulax polyedra to test involvement of this protein in the circadian oxygen evolution rhythm. This involvement was suggested by previous work showing that synthesis of PCP was rhythmic in vivo and in phase with the three-fold rhythm of oxygen evolution. However, Gonyaulax contains six PCP isoforms, only one of which was previously examined. In this report, we extend our analysis to two additional isoforms to encompass roughly 90% of the total cellular PCP. We confirm that synthesis of two additional PCP isoforms is rhythmic in vivo and show that this regulation appears to occur at a translational level as found for two other regulated proteins in this organism. However, PCP is unlikely to be implicated in the oxygen evolution rhythm since both PCP protein levels and the amount of chromophore (OD⁴⁸⁰) bound to protein (OD²⁸⁰) are constant over a circadian period.     

Characterization of the convoluted seminiferous tubule wall. II. Ultrastructural alteration after testis retention in the abdominal cavity

An ultrastructural analysis has been carried out on the seminiferous tubules after different periods of stay of the rat testis in the abdominal cavity. With respect to control rats, no changes are detectable after 5 days, while after 15 and 30 days considerable modifications take place. A number of cellular features are modified, such as the nuclear shape and the perinuclear vesicles, while the cytoplasmic filaments show a less ordered appearance. In addition, the extracellular amorphous matrix undergoes a large increase, due either to an enhanced production or to a reduced turnover related with a lowered cell activity.     

Structure,function and evolution of the signal recognition particle

The signal recognition particle (SRP) is a ribonucleoprotein particle essential for the targeting of signal peptide-bearing proteins to the prokaryotic plasma membrane or the eukaryotic endoplasmic reticulum membrane for secretion or membrane insertion. SRP binds to the signal peptide emerging from the exit site of the ribosome and forms a ribosome nascent chain (RNC)-SRP complex. The RNC-SRP complex then docks in a GTP-dependent manner with a membrane-anchored SRP receptor and the protein is translocated across or integrated into the membrane through a channel called the translocon. Recently considerable progress has been made in understanding the architecture and function of SRP.     

Impact of temperature acclimation on photosynthesis in the toxic red-tide dinoflagellate Alexandriumfundyense (Ca28)

This study assessed the impact of temperature on the photosyntheticactivity in the dinoflagellate Alexandrium fundyense (Ca28)for cultures grown at 75 mol photons m^–2 s^–1 overa range of temperatures. Increasing light intensity under statictemperatures caused a 5-fold decrease in the maximum quantumyield for photosystern II (PSII) (F_vlF_m) Carbon fixation ratesmirrored high-light depressions in (F_vlF_m). Cells in the presenceof streptomycin showed an 83% recovery in (F_vlF_m); therefore,only a minor proportion of the decline in (F_vlF_m)was attributableto PSII damage by bright light. For cells transferred to highertemperatures, F. was less sensitive to high light, decreasingonly 20–40% compared to the 80–90% decrease observedfor cells incubated at their ambient growth temperature. Forcells shifted to higher temperatures, the rapid recovery phaseof (F_vlF_m) was not present; therefore, cells did not initiatedownregulation of PSII. Higher capacity to maintain electrontransport, as indicated by the quantum yields, was confirmedby enhanced carbon fixation. Shifts lower temperatures significantlyincreased PSII sensitivity to high light. Overall, these relationshipsreflect the synergy between photosynthetic light and dark reactionswhich are differentially impacted by changes in temperature.     

Effect of phosphatidylcholine vesicles on the activity of DNA polymerase-α

Summary Phosphatidylcholine vesicles stimulate the activity of the DNA polymerase- from calf thymus. This effect is dependent upon the way of addition of the Mg ions, and the extent of the ³H-dTTP incorporation is closely related to the concentration of the vesicles. A role of phospholipids on the activity of the DNA-related enzymes is suggested.