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Unlike in animals, sperm in flowering plants are immotile and they are embraced as passive cargoes by a pollen tube which embarks on a long journey in the pistil to deliver them to the female gametophyte for fertilization. How the pollen tube switches from a rapid polarized growth towards its target to an abrupt disintegration for sperm cell release inside the female gametophyte is puzzling. Recent studies have shown that members of the Catharanthus roseus RLK1-like (CrRLK1L) receptor kinase family and their ligands, 5-kDa cysteine-rich peptide rapid alkalinization factors (RALFs), engage in an intricate balancing act involving autocrine and paracrine signaling to maintain pollen tube growth and induce timely tube rupture at the spatially confined pollen tube–female gametophyte interface. Here, we review recent progress related to pollen tube integrity control, mainly focusing on the molecular understanding of signaling as well as intracellular signaling nodes in Arabidopsis. Some missing links and future perspectives are also discussed.

Porcine spermatozoa are stored in the oviductal isthmus after natural mating, and the number of spermatozoa is increased in the oviductal ampulla when the mature cumulus-oocyte complexes (COCs) are transferred into the ampulla. However, the mechanism is unclear. Herein, natriuretic peptide type C (NPPC) was mainly expressed in porcine ampullary epithelial cells, whereas its cognate receptor natriuretic peptide receptor 2 (NPR2) was located on the neck and the midpiece of porcine spermatozoa. NPPC increased sperm motility and intracellular Ca2+ levels, and induced sperm release from oviduct isthmic cell aggregates. These actions of NPPC were blocked by the cyclic guanosine monophosphate (cGMP)-sensitive cyclic nucleotide-gated (CNG) channel inhibitor l-cis-Diltiazem. Moreover, porcine COCs acquired the ability to promote NPPC expression in the ampullary epithelial cells when the immature COCs were induced to maturation by epidermal growth factor (EGF). Simultaneously, transforming growth factor-β ligand 1 (TGFB1) levels were dramatically increased in the cumulus cells of the mature COCs. The addition of TGFB1 promoted NPPC expression in the ampullary epithelial cells, and the mature COC-induced NPPC was blocked by the transforming growth factor-β type 1 receptor (TGFBR1) inhibitor SD208. Taken together, the mature COCs promote NPPC expression in the ampullae via TGF-β signaling, and NPPC is required for the release of porcine spermatozoa from the oviduct isthmic cells.

Information on coral reproductive biology and coral spawning times is crucial to advance basic and applied research and inform strategies for coral reef conservation and restoration. Important efforts have been made to collate coral spawning times and reproductive patterns in global and regional datasets. Here, we report and document the first in situ spawning of Pavona maldivensis Gardiner, 1905, observed in the Red Sea. A medium size colony was observed releasing sperm on the full moon night on 23 May 2024, at sunset time. Our observations suggest that the widespread Indo-Pacific P. maldivensis is likely gonochoric. This first report on the in situ spawning timing for P. maldivensis contributes to expanding coral spawning databases and provides valuable data on its reproductive biology, which is relevant for coral restoration and conservation efforts.

Plant movements for survival are nontrivial. Antheridia in the moss Physcomitrium patens (P. patens) use motion to eject sperm in the presence of water. However, the biological and mechanical mechanisms that actuate the process are unknown. Here, the burst of the antheridium of P. patens, triggered by water, results from elastic instability and is determined by an asymmetric change in cell geometry. The tension generated in jacket cell walls of antheridium arises from turgor pressure, and is further promoted when the inner walls of apex burst in hydration, causing water and cellular contents of apex quickly influx into sperm chamber. The outer walls of the jacket cells are strengthened by NAC transcription factor VNS4 and serve as key morphomechanical innovations to store hydrostatic energy in a confined space in P. patens. However, the antheridium in liverwort Marchantia polymorpha (M. polymorpha) adopts a different strategy for sperm release; like jacket cell outer walls of P. patens, the cells surrounding the antheridium of M. polymorpha appear to play a similar role in the storage of energy. Collectively, the work shows that plants have evolved different ingenious devices for sperm discharge and that morphological innovations can differ. The biomechanics of antheridium burst in moss Physcomitrium patens depend on a single layer of jacket cells that store hydrostatic energy, which results from elastic instability and asymmetric changes in cell geometry. By contrast, the antheridium in liverwort Marchantia polymorpha adopts a different strategy for sperm release, and the cells surrounding the antheridium appear to play a dominant role.

Tubulobulbar complexes (TBCs) are actin-based structures that help establish close contact between Sertoli–Sertoli cells or Sertoli–mature germ cells (spermatids) in the seminiferous tubules of the testes. They are actin-rich push-through devices that eliminate excess spermatid cytoplasm and prepare mature spermatids for release into the tubular lumen. Just prior to spermiation, the elongated spermatid interacts with the Sertoli cell via an extensive structure comprising various adhesion molecules called the apical ectoplasmic specialization which is partially replaced by the apical TBC, on the concave surface of the spermatid head. The sperm release process involves extensive restructuring, namely the disassembly and reassembly of junctions at the Sertoli–spermatid interface in the seminiferous epithelium. Based on the presence of different classes of molecules in the TBCs or the defects observed in the absence of TBCs, the main functions attributed to TBCs are elimination of excess spermatid cytoplasm, endocytosis and recycling of junctional molecules, shaping of the spermatid acrosome, and forming transient anchoring devices for mature spermatids before they are released. This review summarizes the recent findings that focus on the role of TBCs in cell cytoskeleton restructuring during sperm release in the testes and the molecular mechanism involved.

The objective of this study was to identify a photolabile period suitable for reducing precocious gonadal maturation in juvenile male sea bass ( Dicentrarchus labrax ) through the exploration of discrete windows of continuous light (LL), 1–2 months in duration, in late summer-early autumn. Somatic growth, 11-ketotestosterone plasma levels, and the rates of testicular maturation and spermiation were analyzed to evaluate the effect of the applied photoperiodic regimes. Three LL treatments, with duration of 2 months each, were previously screened between the months of August and November. Administration of LL during the October–November period failed to show any differential effects in reducing early maturation, as compared to the simulated natural photoperiod. However, the August–September period was considered to be a likely candidate for photolability. To define this photolabile period, four LL treatments with duration of 1 month were then screened within the same late summer period. Our results demonstrate that the time interval including the month of September is the most sensitive photolabile period in order to reduce precocious gametogenesis in sea bass.

We investigated the mechanism of antheridial dehiscence in ferns for the first time using fluorescence microscopy as well as scanning and transmission electron microscopy. The mechanism leading to antheridial dehiscence in Polystichum setiferum, Asplenium trichomanes and A. onopteris was found to depend on the different cellulose contents of the inner and outer walls of the ring cells detected with calcofluor white stain and the Thiéry test. The extremely low cellulose content of the ring cell walls facing spermatozoids made them less mechanically resilient than external wall cells. When the ring cells absorbed water they expanded only into the antheridial cavity, pushing the gametes against the cap cell, which detached from the ring cell below and enabled spermatozoid release. The newly released spermatozoids were spherical bodies covered in cellulose fibrils. The significance of cellulose fibrils could be to isolate the gametes from each other, to reinforce the electron transparent material and to protect the gamete from pressure created by the ring cells during release.

In the marine polychaete, Platynereis dumerilii, reproductive behavior in the two sexes is synchronized by the consecutive discharge of male and female sex-specific pheromones. After the female releases the eggs into the free water column, immediate fertilization is achieved by several males circling around the eggs emitting sperm clouds. We report the isolation and identification of the sperm-release pheromone present in the coelomic fluid of sexually mature females. Each step in isolation was guided by bioassay. Isolation methods included extraction and solvent partitioning and separation methods included ultrafiltration and high-performance liquid chromatography. Uric acid was identified as the sperm-release pheromone that is discharged by the female with release of the eggs. The threshold concentration for sperm release by males was determined as 0.6 μM.[PUBLICATION ABSTRACT]

We investigated breeding readiness of selected migrant species captured at a known stopover site in western New York during the spring of 1995 and 1996. A total of 775 individuals representing 14 species were examined for outward physiological indication of male breeding readiness measured by relative size of cloacal protuberance. Only 2 of the 775 individuals exhibited a cloacal protuberance, both being captured in 1996; one Ruby-crowned Kinglet (Regulus calendula) and one Swainson's Thrush (Catharus minimus). Cloacal lavage samples were taken from 22 White-throated Sparrows (Zonotrichia albicollis) and 26 Swainson's Thrushes during the spring of 1996. None of the migrating individuals lavaged exhibited presence of cloacal sperm regardless of species, sex, time, or date of capture. Poor energetic condition was typical of these captured migratory landbirds. Depleted energetic stores may explain the lack of early sperm production in migrants at this stopover site.