Caenorhabditis elegans oocytes, like those of most animals, arrest during meiotic prophase. Sperm promote the resumption of meiosis (maturation) and contraction of smooth muscle-like gonadal sheath cells, which are required for ovulation. We show that the major sperm cytoskeletal protein (MSP) is a bipartite signal for oocyte maturation and sheath contraction. MSP also functions in sperm locomotion, playing a role analogous to actin. Thus, during evolution, MSP has acquired extracellular signaling and intracellular cytoskeletal functions for reproduction. Proteins with MSP-like domains are found in plants, fungi, and other animals, suggesting that related signaling functions may exist in other phyla.

During sexual reproduction in most animals, oocytes arrest in meiotic prophase and resume meiosis (meiotic maturation) in response to sperm or somatic cell signals. Despite progress in delineating mitogen-activated protein kinase (MAPK) and CDK/cyclin activation pathways involved in meiotic maturation, it is less clear how these pathways are regulated at the cell surface. The Caenorhabditis elegans major sperm protein (MSP) signals oocytes, which are arrested in meiotic prophase, to resume meiosis and ovulate. We used DNA microarray data and an in situ binding assay to identify the VAB-1 Eph receptor protein-tyrosine kinase as an MSP receptor. We show that VAB-1 and a somatic gonadal sheath cell-dependent pathway, defined by the CEH-18 POU-class homeoprotein, negatively regulate meiotic maturation and MAPK activation. MSP antagonizes these inhibitory signaling circuits, in part by binding VAB-1 on oocytes and sheath cells. Our results define a sperm-sensing control mechanism that inhibits oocyte maturation, MAPK activation, and ovulation when sperm are unavailable for fertilization. MSP-domain proteins are found in diverse animal taxa, where they may regulate contact-dependent Eph receptor signaling pathways. Sexual reproduction requires meiosis to generate haploid (1n) gamete nuclei, which unite after fertilization to form the diploid (2n) totipotent embryo. Despite this universal requirement, meiosis is regulated differently in sperm and oocytes. Whereas sperm proceed through the meiotic divisions uninterrupted, oocytes almost invariably arrest during one, and sometimes two stages following premeiotic DNA replication and meiotic recombination, depending on the species. Therefore, the completion of meiosis in oocytes must be coordinated with development and fertilization to ensure successful reproduction. To achieve this coordination, sperm and somatic cell signals regulate oocyte meiotic progression by activating downstream cyclin-dependent kinase regulatory pathways, which mediate cell cycle transitions in eukaryotes (for review, see Ferrell 1999; Masui 2001).The oocytes of most animals, including the early-diverging sponges and cnidarians (Masui 1985), arrest during meiotic prophase, suggesting that this regulatory mechanism represents a fundamental metazoan reproductive strategy. Human oocytes can remain arrested in prophase for several decades, and aberrant regulation of the first meiotic division is a major cause of infertility, miscarriage, and chromosomal nondisjunction (for review, see Jacobs 1992; Hunt and LeMaire-Adkins 1998). In most animals examined, meiosis resumes in response to nonautonomous signals through a process termed meiotic maturation, which prepares the oocyte for fertilization and embryogenesis. The hallmarks of meiotic maturation include nuclear envelope breakdown, cortical cytoskeletal rearrangement, and meiotic spindle assembly. Studies of Xenopus have identified two key intracellular enzymes, maturation-promoting factor (MPF), a complex consisting of the regulatory protein cyclin B...

The major sperm protein (MSP) is the central cytoskeletal element required for actin-independent motility of nematode spermatozoa. MSP has a dual role in Caenorhabditis elegans reproduction, functioning as a hormone for both oocyte meiotic maturation and ovarian muscle contraction. The identification of the signaling function of MSP raised the question, how do spermatozoa, which are devoid of ribosomes, ER and Golgi, release a cytoplasmic protein lacking a signal sequence? Here, we provide evidence that MSP export occurs by the budding of novel vesicles that have both inner and outer membranes with MSP sandwiched in between. MSP vesicles are apparently labile structures that generate long-range MSP gradients for signaling at the oocyte cell surface. Both spermatozoa and non-motile spermatids bud MSP vesicles, but their stability and signaling properties differ. Budding protrusions from the cell body contain MSP, but not the MSD proteins, which counteract MSP filament assembly. We propose that MSP generates the protrusive force for its own vesicular export.

The Polo-like kinases are key regulatory molecules required during the cell cycle for the successful completion of mitosis. We have cloned a C. elegans homolog of the Drosophila melanogaster polo gene (designated plk-1 for C. elegans polo-like kinase-1) and present the subcellular localization of the PLK-1 protein during the meiotic and mitotic cell cycles in C. elegans oocytes and embryos, respectively. Disruption of PLK-1 expression by RNA-mediated interference (RNAi) disrupts normal oocyte and embryonic development. Inspection of oocytes revealed a defect in nuclear envelope breakdown (NEBD) before ovulation. This defect in NEBD was also observed in oocytes that were depleted of the cyclin-dependent kinase NCC-1 (C. elegans homolog of Cdc2). The plk-1 RNAi oocytes were fertilized; however the resulting embryos were unable to separate their meiotic chromosomes or form and extrude polar bodies. These defects led to embryonic arrest as single cells. genesis 26:26 -41, 2000.

Maturation promoting factor (MPF), a complex of cyclin-dependent kinase 1 and cyclin B, drives oocyte maturation in all animals. Mechanisms to block MPF activation in developing oocytes must exist to prevent precocious cell cycle progression prior to oocyte maturation and fertilization. This study sought to determine the developmental consequences of precociously activating MPF in oocytes prior to fertilization. Whereas depletion of Myt1 in Xenopus oocytes causes nuclear envelope breakdown in vitro, we found that depletion of the Myt1 ortholog WEE-1.3 in C. elegans hermaphrodites causes precocious oocyte maturation in vivo. Although such oocytes are ovulated, they are fertilization incompetent. We have also observed novel phenotypes in these precociously maturing oocytes, such as chromosome coalescence, aberrant meiotic spindle organization, and the expression of a meiosis II postfertilization marker. Furthermore, co-depletion studies of CDK-1 and WEE-1.3 demonstrate that WEE-1.3 is dispensable in the absence of CDK-1, suggesting that CDK-1 is a major target of WEE-1.3 in C. elegans oocytes.

Background and aims-To investigate the importance of lipase on gastric functions, we studied the eVects of orlistat, a potent and specific inhibitor of lipase, on postprandial gastric acidity and gastric emptying of fat. Methods-Fourteen healthy volunteers participated in a double blind, placebo controlled, randomised study. In a two way cross over study with two test periods of five days, separated by at least 14 days, orlistat 120 mg three times daily or placebo was given with standardised daily meals. In previous experiments we found that this dose almost completely inhibited postprandial duodenal lipase activity. Subjects underwent 28 hour intragastric pH-metry on day 4, and a gastric emptying study with a mixed meal (800 kcal) labelled with 999m Tc sulphur colloid (solids) and 111In thiocyanate (fat) on day 5. Gastric pH data were analysed for three postprandial hours and the interdigestive periods. Results-Orlistat inhibited almost completely (by 75%) lipase activity and accelerated gastric emptying of both the solid (by 52%) and fat (by 44%) phases of the mixed meal (p<0.03). Orlistat increased postprandial gastric acidity (from a median pH of 3.3 to 2.7; p<0.01). Postprandial cholecystokinin release was lower with orlistat (p<0.03). Conclusion-Lipase has an important role in the regulation of postprandial gastric acid secretion and fat emptying in humans. These eVects might be explained by lipolysis induced release of cholecystokinin. (Gut 2000;46:774-781)

The CDC25 dual-specificity phosphatase family has been shown to play a key role in cell cycle regulation. The phosphatase activity of CDC25 drives the cell cycle by removing inhibitory phosphates from cyclin-dependent kinase/cyclin complexes. Although the regulation of CDC25 phosphatase activity has been elucidated both biochemically and genetically in other systems, the role of this enzyme during development is not well understood. To examine the expression pattern and function of CDC25 in Caenorhabditis elegans, we characterized a cdc25 homolog, cdc-25.1, during early embryonic development. The CDC-25.1 protein localizes to oocytes, embryonic nuclei, and embryonic cortical membranes. When the expression of CDC-25.1 was disrupted by RNA-mediated interference, the anterior cortical membrane of fertilized eggs became very fluid during meiosis and subsequent mitotic cell cycles. Mispositioning of the meiotic spindle, defects in polar body extrusion and chromosome segregation, and abnormal cleavage furrows were also observed. We conclude that CDC-25.1 is required for a very early developmental process-the proper completion of meiosis prior to embryogenesis.

Intercellular communication plays a pivotal role in regulating and coordinating oocyte meiosis and fertilization, key triggers for embryonic development. The nematode Caenorhabaditis elegans has emerged as an important experimental paradigm for exploring these fundamental reproductive processes and their regulation. The oocytes of most animal species arrest during meiotic prophase and complete meiosis in response to intercellular signaling in the process of meiotic maturation. Oocyte meiotic maturation is defined by the transition between diakinesis and metaphase of meiosis I and is accompanied by nuclear envelope breakdown and meiotic spindle assembly. As such, the meiotic maturation process is essential for completing meiosis and a prerequisite for successful fertilization. In C. elegans, the processes of meiotic maturation, ovulation, and fertilization are temporally coupled: sperm utilize the major sperm protein as a hormone to trigger oocyte meiotic maturation, and, in turn, the maturing oocyte signals its own ovulation, leading to fertilization. The powerful genetic screens possible in C. elegans have led to the identification of several sperm cell surface proteins that are required for the interaction and fusion of gametes at fertilization. The study of these proteins provides fundamental insights into fertilization mechanisms, their role in speciation, and their potential conservation across phyla. Signaling processes sparked by fertilization are required for meiotic chromosome segregation and initiating the embryonic program. Here we review recent advances in understanding how signaling mechanisms contribute to the oocyte-to-embryo transition in C. elegans. Developmental Dynamics 235:571-585, 2006.