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.

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.

Contents Summary 687 I. Introduction 687 II. Pollen tube membrane-localized receptors coordinate cell integrity and sperm release 689 III. RALF peptides mediate autocrine and paracrine signaling 689 IV. ROS and ion channel signaling mediate intracellular response 690 V. Involvements from pollen tube cell wall components 690 VI. Concluding remarks 691 Acknowledgements 692 Author contributions 692 References 692 SUMMARY: 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.

BACKGROUND: Spermiation is a process of releasing sperm into the lumen of seminiferous tubules. Failure in releasing sperm into the lumen is designated as spermiation defect. Spermiation defect cases present as oligo-azoospermia or azoospermia despite normal gonadotropins and testicular histology/cytology. Human spermiation defect never got attention to investigate infertility practice. Most of the information on spermiation defect, so far is from animal experiments. We assume some cases of non-obstructive azoospermia with normal gonadotropins and testicular histology/cytology could be due to spermiation defect.
OBJECTIVE: The aim of the study was to find out the underlying aetiology in cases of human spermiation defect.
METHODS: A total of 13 cases of spermiation defect and 20 fertile men as control constituted study material. Cases were studied for chromosomal abnormalities by conventional karyotyping, sex chromosome mosaicism by interphase XY FISH, Yq microdeletion by STS PCR, sertoli cell quality (function) and quantity (numbers) by serum Anti-Mullerian Hormone (AMH) and inhibin B besides other hormones like Follicular Stimulating Hormone (FSH), prolactin, testosterone and estradiol. Vitamin A concentration in serum was also measured. Presence of heavy metal was investigated by elemental electron microscopy in seminal cells (eight cases) & by spectrometry in serum as well as seminal plasma.
RESULTS: Chromosomal and Yq microdeletion study failed to detect any abnormalities. AMH, inhibin B and vitamin A were also normal. Estradiol level was high in 6 out of 13 cases (46%) while platinum in seminal cells was high in 4 cases (50%). High (four times or more) serum level of lead and nickel was observed in 11 (85%) and 6 (46%) cases, respectively.
CONCLUSIONS: High serum concentration of heavy metals like lead & nickel or high platinum accumulation in seminal cells or high serum estradiol alone or in combinations may be underlying aetiologic factors in human spermiation defect.

Tubulobulbar complexes are elaborate clathrin/actin related structures that form at sites of intercellular attachment in the seminiferous epithelium of the mammalian testis. Here we summarize what is currently known about the morphology and molecular composition of these structures and review evidence that the structures internalize intercellular junctions both at apical sites of Sertoli cell attachment to spermatids, and at basal sites where Sertoli cells form the blood-testis barrier. We present updated models of the sperm release and spermatocyte translocation mechanisms that incorporate tubulobulbar complexes into their designs.

Sex pheromones rapidly affect endocrine physiology and behaviour, but little is known about their effects on gene expression in the neural tissues that mediate olfactory processing. In this study, we exposed male goldfish for 6h to waterborne 17,20βP (4.3 nM) and PGF2α (3 nM), the main pre-ovulatory and post-ovulatory pheromones, respectively. Both treatments elevated milt volume (P=0.001). Microarray analysis of male telencephalon following PGF2α treatment identified 71 unique transcripts that were differentially expressed (q<5%; 67 up, 4 down). Functional annotation of these regulated genes indicates that PGF2α pheromone exposure affects diverse biological processes including nervous system functions, energy metabolism, cholesterol/lipoprotein transport, translational regulation, transcription and chromatin remodelling, protein processing, cytoskeletal organization, and signalling. By using real-time RT-PCR, we further validated three candidate genes, ependymin-II, calmodulin-A and aldolase C, which exhibited 3-5-fold increase in expression following PGF2α exposure. Expression levels of some other genes that are thought to be important for reproduction were also determined using real-time RT-PCR. Expression of sGnRH was increased by PGF2α, but not 17,20βP, whereas cGnRH expression was increased by 17,20βP but not PGF2α. In contrast, both pheromones increase the expression of glutamate (GluR2a, NR2A) and γ-aminobutyric acid (GABAA γ2) receptor subunit mRNAs. Milt release and rapid modulation of neuronal transcription are part of the response of males to female sex pheromones.