reproduction
why research in C.elegans reproduction is an important first step to studying ourselves

four C.elegans spermatozoa Basics about C.elegans reproduction

Reproduction in C. elegans involves two sexes, males and hermaphrodites. Hermaphrodites are females that produce sperm, which the hermaphrodite worm can use to self-fertilize the first 300 or so eggs. After self-fertilizing the first batch of eggs, the hermaphrodite preferentially accepts sperm from males in hopes of producing a larger number of offspring. this unusual mating system makes males nonessential - which is convenient for molecular biologists because it allows them to mutate males without altering the viability of the test strain. The picture on the left shows four C.elegans spermatozoa.




Why use C.elegans genome?

The completed sequence of the C. elegans genome allowed the prediction of nearly all the genes in this animal that permit it to develop from a fertilized egg, to learn and behave, to mate and reproduce, and to age. (C. elegans Sequencing Consortium, 1998). DNA microarrays can be used to rapidly assess the expression of many genes in parallel and thus determine gene expression patterns on a global scale (Schena et al., 1995). The completed C. elegans sequence allows DNA microarrays to be constructed that contain not only known genes but also previously unstudied genes.

click here to see what a DNA microarray looks like and a diagram of how it's done





How is the genome used for the study of reproduction?

DNA microarrays containing genomic PCR products corresponding to 11,917 (92% of the genome) of the C. elegans genes were produced (Saffman and Lasko, 1999). Purified RNA from worm populations that make either oocytes only (worms mutated in a gene called fem-1, which can't make sperm), or sperm only (fem-3 mutants, which make no oocytes) were taken (Saffman and Lasko, 1999). They were labeled with two RNA preparations with different colored dyes, and added to a microarray that contained several hundred worm genes. By determining which genes were expressed only in the worms that make sperm, an identification of some of the genes that allow these cells to develop, move towards the unfertilized egg, and fuse with it, were made. A few germline-intrinsic and sperm-enriched genes were found on the X chromosome, while oocyte-enriched genes were evenly distributed throughout the genome (Saffman and Lasko, 1999).



cross section of a worm spermatozoa



Contribution to the study of humans:

The experimental overview can be used to compare global profiles of germline gene expression in humans, to those from other tissues and to search for interesting global control mechanisms of gene regulation. Research can now be done in areas of aging, development, reproduction, infertility and various diseases. These new approaches can be used to learn and understand more about the human body and its reaction to such diseases. The microarray analysis of the genome has provided a list of most of the genes that participate in the biological processes that make the germline unique (Saffman and Lasko, 1999). This list can now be used to search for genes that act in diverse germline functions, such as down- stream targets of signaling pathways or RNA-binding proteins, new recombination and meiosis genes, or new genes with sperm-specific functions (Saffman and Lasko, 1999). The full-genome DNA microarrays show the relative levels of gene expression for nearly every gene during development, from eggs through adulthood.



references

1. C. elegans Sequencing Consortium. (1998). Genome sequence of the nematode C. elegans: a platform for investigating biology. Science 282, 2012-2018.

2. Saffman EE. Lasko P. (1999) Germline development in vertebrates and invertebrates. Cellular & Molecular Life Sciences. 55(8-9):1141-63, 1999 Jul.

3. Schena, M., Shalon, D., Davis, R.W., and Brown, P.O. (1995). Quantitative monitoring of gene expression patterns with a complementary DNA microarray. Science 270, 467-470.

4. Pictures on this page, used by permission, courtesy of Wardlab, Arizona.