Abstract
Sexual reproduction depends upon meiosis for the generation of haploid gamete nuclei, which unite after fertilization to form the diploid zygote. The oocytes of most animal species arrest during meiotic prophase, and complete meiosis in response to intercellular signaling in a process called meiotic maturation. Oocyte meiotic maturation is defined by the transition between diakinesis and metaphase of meiosis I and is accompanied by nuclear envelope breakdown, rearrangement of the cortical cytoskeleton, and meiotic spindle assembly. Thus, the meiotic maturation process is essential for meiosis and prepares the oocyte for 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 thereby facilitating fertilization. This chapter highlights recent advances in understanding meiotic maturation signaling and gametic interactions required for fertilization.
Highlights
OverviewOocyte meiotic maturation must be coordinated with other cellular events during oogenesis, including growth, meiotic chromosome reorganization, and ovulation
major sperm protein (MSP) promotes oocyte meiotic maturation, in part by binding the VAB-1 Eph receptor protein-tyrosine kinase on oocytes, and in part by antagonizing an inhibitory somatic gonadal sheath cell pathway (Miller et al, 2003)
Miller et al (2001) demonstrated that the major sperm protein (MSP), the central cytoskeletal element required for the actin-independent motility of nematode spermatozoa, has a dual role in C. elegans reproduction, functioning as a hormone for oocyte meiotic maturation and gonadal sheath cell contraction
Summary
Oocyte meiotic maturation must be coordinated with other cellular events during oogenesis, including growth, meiotic chromosome reorganization, and ovulation To achieve this coordination, intercellular signals regulate oocyte meiotic progression (reviewed by Ferrell, 1999; Masui, 2001). The timing of the meiotic divisions with respect to fertilization varies among species, likely reflecting the diversity of reproductive strategies observed in nature (Figure 1) Despite these differences in timing, extensive studies reveal striking conservation in the molecular underpinnings of oocyte meiotic maturation among different animals. Oocytes develop in close association with proximal gonadal sheath cells (Figure 2), smooth muscle-like cells that regulate meiotic maturation and contract to drive ovulation (McCarter et al, 1997; Hall et al, 1999; Miller et al, 2003). The MSP hormone functions as the linchpin of a sperm-sensing mechanism linking meiotic maturation and sperm availability, thereby ensuring fertilization
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