[
WormBook,
2006]
Physiological methods entered the world of C. elegans, a model system used for many years to study development and a plethora of biological processes mainly employing genetic, molecular and anatomical techniques. One of the methods introduced by physiologists is the use of Xenopus oocytes for expression of C. elegans ion channels. Oocytes of the South African frog Xenopus laevis are used widely for the expression of mammalian channels and transporters contributing to numerous discoveries in these fields. They now promise to aid C. elegans researchers in deciphering mechanisms of channels function and regulation with implications for mammalian patho-physiology. Heterologous cRNA can be easily injected into Xenopus oocytes and translated proteins can be studied using several techniques including electrophysiology, immunocytochemistry and protein biochemistry. This chapter will focus on techniques used for oocyte preparation and injection, and will give a brief overview of specific methods. Limitations of the use of Xenopus oocytes will be also discussed.
[
WormBook,
2005]
Cell-division control affects many aspects of development. Caenorhabditis elegans cell-cycle genes have been identified over the past decade, including at least two distinct Cyclin-Dependent Kinases (CDKs), their cyclin partners, positive and negative regulators, and downstream targets. The balance between CDK activation and inactivation determines whether cells proceed through G 1 into S phase, and from G 2 to M, through regulatory mechanisms that are conserved in more complex eukaryotes. The challenge is to expand our understanding of the basic cell cycle into a comprehensive regulatory network that incorporates environmental factors and coordinates cell division with growth, differentiation and tissue formation during development. Results from several studies indicate a critical role for CKI-1 , a CDK inhibitor of the Cip/Kip family, in the temporal control of cell division, potentially acting downstream of heterochronic genes and dauer regulatory pathways.
[
WormBook,
2006]
There are two sexes in C. elegans, hermaphrodite and male. While there are many sex-specific differences between males and hermaphrodites that affect most tissues, the basic body plan and many of its structures are identical. However, most structures required for mating or reproduction are sexually dimorphic and are generated by sex-specific cell lineages. Thus to understand cell fate specification in hermaphrodites, one must consider how the body plan, which is specified during embryogenesis, influences the fates individual cells. One possible mechanism may involve the asymmetric distribution of POP-1 /Tcf, the sole C. elegans Tcf homolog, to anterior-posterior sister cells. Another mechanism that functions to specify cell fates along the anterior-posterior body axis in both hermaphrodites and males are the Hox genes. Since most of the cell fate specifications that occur in hermaphrodites also occur in males, the focus of this chapter will be on those that only occur in hermaphrodites. This will include the cell fate decisions that affect the HSN neurons, ventral hypodermal P cells, lateral hypodermal cells V5 , V6 , and T ; as well as the mesodermal M, Z1 , and Z4 cells and the intestinal cells. Both cell lineage-based and cell-signaling mechanisms of cell fate specification will be discussed. Only two direct targets of the sex determination pathway that influence cell fate specification to produce hermaphrodite-specific cell fates have been identified. Thus a major challenge will be to learn additional mechanisms by which the sex determination pathway interacts with signaling pathways and other cell fate specification genes to generate hermaphrodite-specific cell fates.