[
WormBook,
2005]
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.
[
WormBook,
2005]
The morphogenesis of the C. elegans embryo is largely controlled by the development of the epidermis, also known as the hypodermis, a single epithelial layer that surrounds the animal. Morphogenesis of the epidermis involves cell-cell interactions with internal tissues, such as the developing nervous system and musculature. Genetic analysis of mutants with aberrant epidermal morphology has defined multiple steps in epidermal morphogenesis. In the wild type, epidermal cells are generated on the dorsal side of the embryo among the progeny of four early embryonic blastomeres. Specification of epidermal fate is regulated by a hierarchy of transcription factors. After specification, dorsal epidermal cells rearrange, a process known as dorsal intercalation. Most epidermal cells fuse to generate multinucleate syncytia. The dorsally located epidermal sheet undergoes epiboly to enclose the rest of the embryo in a process known as ventral enclosure; this movement requires both an intact epidermal layer and substrate neuroblasts. At least three distinct types of cellular behavior underlie the enclosure of different regions of the epidermis. Following enclosure, the epidermis elongates, a process driven by coordinated cell shape changes. Epidermal actin microfilaments, microtubules, and intermediate filaments all play roles in elongation, as do body wall muscles. The final shape of the epidermis is maintained by the collagenous exoskeleton, secreted by the apical surface of the epidermis.