In the preovulatory ovarian follicle, mammalian oocytes are maintained in prophase meiotic arrest until the luteinizing hormone (LH) surge induces reentry into the first meiotic division. Dramatic changes in the somatic cells surrounding the oocytes and in the follicular wall are also induced by LH and are necessary for ovulation. Here, we provide genetic evidence that LH-dependent transactivation of the epidermal growth factor receptor (EGFR) is indispensable for oocyte reentry into the meiotic cell cycle, for the synthesis of the extracellular matrix surrounding the oocyte that causes cumulus expansion, and for follicle rupture in vivo. Mice deficient in either amphiregulin or epiregulin, two EGFR ligands, display delayed or reduced oocyte maturation and cumulus expansion. In compound-mutant mice in which loss of one EGFR ligand is associated with decreased signaling from a hypomorphic allele of the EGFR, LH no longer signals oocyte meiotic resumption. Moreover, induction of genes involved in cumulus expansion and follicle rupture is compromised in these mice, resulting in impaired ovulation. Thus, these studies demonstrate that LH induction of epidermal growth factor-like growth factors and EGFR transactivation are essential for the regulation of a critical physiological process such as ovulation and provide new strategies for manipulation of fertility.The luteinizing hormone (LH) surge plays a central role in promoting a cascade of events in ovarian preovulatory follicles that are essential for the ovulation of a fertilizable oocyte. Acting through LH-chorionic gonadotropin (LH-CG) receptors (LHRs) (LHR is a member of the G protein-coupled receptor superfamily encoded by Lhcgr), LH induces reprogramming of the gene expression profiles of follicular somatic cells (theca and granulosa cells), changes in the secretory properties of the cumulus cells surrounding the oocyte and cumulus expansion, oocyte reentry into the meiotic cell cycle, and follicle rupture (7, 41). LHRs are highly expressed on the granulosa cells lining the antral cavity of preovulatory follicles (mural granulosa cells) and on the external theca cells that are in continuity with the surrounding stroma. However, within preovulatory follicles, oocytes and cumulus cells that are profoundly affected by the LH surge express few or no LHRs and fail to respond when directly exposed to LH in vitro (37).To explain how LH signals are propagated from the periphery toward the cumulus oocyte complex (COC), a model has been proposed whereby factors released by mural granulosa cells function in an autocrine and paracrine manner to transduce the LH effects within the follicle (34). Secretion of bioactive growth factors from the oocyte to affect somatic cells is well established (27,30); conversely, the paracrine signals originating from the somatic cells and affecting oocytes have long been sought but are largely unknown. Recently, we have proposed that intrafollicular release of members of the epidermal growth factor (EGF)-like family (34) may fulfill this ...

Chemical mutagenesis in the mouse is a powerful approach for phenotype-driven genetics, but questions remain about the efficiency with which new mutations ascertained by their phenotype can be localized and identified, and that knowledge applied to a specific biological problem. During a global screen for dominant phenotypes in about 30,000 animals, a novel class of pigmentation mutants were identified by dark skin (Dsk). We determined the genetic map location, homozygous phenotype, and histology of 10 new Dsk and 2 new dark coat (Dcc) mutations, and identified mutations in Agouti (Met1Leu, Dcc4), Sox18 (Leu220ter, Dcc1), Keratin 2e (Thr500Pro, Dsk2), and Egfr (Leu863Gln, Dsk5). Cutaneous effects of most Dsk mutations are limited to melanocytes, except for the Keratin 2e and Egfr mutations, in which hyperkeratosis and epidermal thickening precede epidermal melanocytosis by 3-6 wk. The Dsk2 mutation is likely to impair intermediate filament assembly, leading to cytolysis of suprabasal keratinocytes and secondary hyperkeratosis and melanocytosis. The Dsk5 mutation causes increased tyrosine kinase activity and a decrease in steady-state receptor levels in vivo. The Dsk mutations represent genes or map locations not implicated previously in pigmentation, and delineate a developmental pathway in which mutations can be classified on the basis of body region, microscopic site, and timing of pigment accumulation.

Background and Purpose-Patterns and mechanisms of stroke in patients with atherosclerotic middle cerebral artery (MCA) disease remain unclear. We sought to identify lesion patterns and stroke mechanisms associated with MCA disease using early diffusion-weighted imaging (DWI). Methods-We reviewed 185 acute ischemic stroke patients who had (1) symptomatic lesions located in the unilateral MCA territory on DWI performed within 48 hours of symptom onset, and (2) either corresponding MCA disease, internal carotid artery disease, or cardioembolism. Acute DWI lesion patterns were classified as (1) single (small perforator Ͻ2 cm; large perforator Ն2 cm; pial; large territorial; border-zone) and (2) multiple. Results-MCA disease was diagnosed in 63 patients, 32 (50.8%) of whom showed multiple lesions. Concomitant perforator and pial infarcts (14/63, PϽ0.001), concomitant perforator, pial, and border-zone infarcts (9/63, PϽ0.001), and single small perforator infarcts (12/63, Pϭ0.001) were identified more often in patients with MCA disease than in those with cardioembolism or internal carotid artery disease. Small perforator infarcts were more common in patients with milder stenosis than with severe stenosis or occlusion of MCA (PϽ0.001). Whether they occurred singly or in addition to other lesions, pial infarcts were identified more often in patients with severe stenosis or occlusion of MCA (Pϭ0.001). Conclusions-Perforating artery infarcts, whether single or occurring in addition to pial or border-zone infarcts, are lesion patterns specific for MCA disease. This suggests that local branch occlusion and coexisting distal embolization may be a common stroke mechanism in patients with MCA disease.