Mammalian oocytes are arrested in meiotic prophase by an inhibitory signal from the surrounding somatic cells in the ovarian follicle. In response to luteinizing hormone (LH), which binds to receptors on the somatic cells, the oocyte proceeds to second metaphase, where it can be fertilized. Here we investigate how the somatic cells regulate the prophase-to-metaphase transition in the oocyte, and show that the inhibitory signal from the somatic cells is cGMP. Using FRET-based cyclic nucleotide sensors in follicleenclosed mouse oocytes, we find that cGMP passes through gap junctions into the oocyte, where it inhibits the hydrolysis of cAMP by the phosphodiesterase PDE3A. This inhibition maintains a high concentration of cAMP and thus blocks meiotic progression. LH reverses the inhibitory signal by lowering cGMP levels in the somatic cells (from ~2 μM to ~80 nM at 1 hour after LH stimulation) and by closing gap junctions between the somatic cells. The resulting decrease in oocyte cGMP (from ~1 μM to ~40 nM) relieves the inhibition of PDE3A, increasing its activity by ~5-fold. This causes a decrease in oocyte cAMP (from ~700 nM to ~140 nM), leading to the resumption of meiosis.

Luteinizing hormone (LH) acts on ovarian follicles to reinitiate meiosis in prophase-arrested mammalian oocytes, and this has been proposed to occur by interruption of a meioisis-inhibitory signal that is transmitted through gap junctions into the oocyte from the somatic cells that surround it. To investigate this idea, we microinjected fluorescent tracers into live antral follicle-enclosed mouse oocytes, and we demonstrate for the first time that LH causes a decrease in the gap junction permeability between the somatic cells, prior to nuclear envelope breakdown (NEBD). The decreased permeability results from the MAP kinase-dependent phosphorylation of connexin 43 on serines 255, 262 and 279/282. We then tested whether the inhibition of gap junction communication was sufficient and necessary for the reinitiation of meiosis. Inhibitors that reduced gap junction permeability caused NEBD, but an inhibitor of MAP kinase activation that blocked gap junction closure in response to LH did not prevent NEBD. Thus, both MAP kinase-dependent gap junction closure and another redundant pathway function in parallel to ensure that meiosis resumes in response to LH.

The meiotic cell cycle in mouse oocytes is arrested in prophase, and then restarted when luteinizing hormone (LH) acts on the surrounding granulosa cells. The granulosa cells keep meiosis arrested by providing a source of cGMP that diffuses into the oocyte through gap junctions, and LH restarts the cell cycle by closing the junctions and by decreasing granulosa cell cGMP, thus lowering oocyte cGMP. Epidermal growth factor receptor (EGFR) activation is an essential step in triggering LH-induced meiotic resumption, but its relationship to the cGMP decrease in the follicle is incompletely understood, and its possible function in causing gap junction closure has not been investigated. Here we use EGFR agonists (epiregulin and amphiregulin), and an EGFR kinase inhibitor (AG1478) to study the function of the EGFR in the signaling pathways leading to the release of oocytes from prophase arrest. Our results indicate that the EGFR kinase contributes to LH-induced meiotic resumption in two different ways. First, it is required for gap junction closure. Second, it is required for an essential component of the decrease in follicle cGMP. Our data show that the EGFR kinase-dependent component of the cGMP decrease is required for LH-induced meiotic resumption, but they also indicate that an as yet unidentified pathway accounts for a large part of the cGMP decrease.

The maintenance of meiotic prophase arrest in fully grown vertebrate oocytes depends on the activity of a G(s) G-protein that activates adenylyl cyclase and elevates cAMP, and in the mouse oocyte, G(s) is activated by a constitutively active orphan receptor, GPR3. To determine whether the action of luteinizing hormone (LH) on the mouse ovarian follicle causes meiotic resumption by inhibiting GPR3-G(s) signaling, we examined the effect of LH on the localization of Galpha(s). G(s) activation in response to stimulation of an exogenously expressed beta(2)-adrenergic receptor causes Galpha(s) to move from the oocyte plasma membrane into the cytoplasm, whereas G(s) inactivation in response to inhibition of the beta(2)-adrenergic receptor causes Galpha(s) to move back to the plasma membrane. However, LH does not cause a change in Galpha(s) localization, indicating that LH does not act by terminating receptor-G(s) signaling.

c Chronic tegumentary leishmaniasis is characterized by a scarcity of parasites in lesions and a heightened inflammatory response. Deregulated and hyperactive inflammation contributes to tissue damage and parasite persistence. The mechanisms by which immune cells are recruited to the lesion and their relationship to clinical outcomes remain elusive. We examined the expression levels of chemokines and their receptors in relation to clinical outcome in dermal leishmaniasis caused by Leishmania (Viannia) panamensis. Primary macrophages from healthy donors were infected with L. panamensis strains isolated from self-healing patients (n ‫؍‬ 4) and those presenting chronic disease (n ‫؍‬ 5). A consistent pattern of upregulation of neutrophil (cxcl1, cxcl2, cxcl5, and cxcl8/il-8) and monocyte (ccl2, ccl7, ccl8, cxcl3, and cxcl10) chemotactic chemokines and ccr1 and ccr5 receptor genes, evaluated by reverse transcription-quantitative PCR (qRT-PCR), was observed upon infection with strains from patients with chronic dermal leishmaniasis; induction of CXCL5 and CCL8 was corroborated at the protein level. No apparent upregulation was elicited in macrophages infected with strains from self-healing patients. Expression levels of ccl8, cxcl2, cxcl3, and cxcl5 in lesion biopsy specimens from patients with chronic cutaneous leishmaniasis (CL) were compared to those in biopsy specimens from Montenegro skin tests of individuals with asymptomatic infection. Increased expression levels of cxcl5 (P < 0.05), ccl8, and cxcl3 were corroborated in chronic CL lesions. Our study revealed a dichotomy in macrophage chemokine gene expression elicited by L. panamensis strains from patients with self-healing disease and those presenting chronic disease, consistent with parasite-mediated hyperactivation of the inflammatory response driving chronicity. The predominant upregulation of neutrophil and monocyte chemoattractants indicates novel mechanisms of sustained inflammatory activation and may provide new therapeutic targets against chronic dermal leishmaniasis.