Function of the her-1 gene is required for maintenance of male differentiation in adult tissues of C. elegans

Competence for chemical reprogramming of sexual fate correlates with an intersexual molecular signature in Caenorhabditis elegans

In multicellular organisms, genetic programs guide cells to adopt cell fates as tissues are formed during development, maintained in adults, and repaired after injury. Here we explore how a small molecule in the environment can switch a genetic program from one fate to another. Wild-type Caenorhabditis elegans XX adult hermaphrodites make oocytes continuously, but certain mutant XX adults make sperm instead in an otherwise hermaphrodite soma. Thus, puf-8; lip-1 XX adults make only sperm, but they can be switched from sperm to oocyte production by treatment with a small-molecule MEK inhibitor. To ask whether this chemical reprogramming is common, we tested six XX sperm-only mutants, but found only one other capable of cell fate switching, fbf-1; lip-1. Therefore, reprogramming competence relies on genotype, with only certain mutants capable of responding to the MEK inhibitor with a cell fate change. To gain insight into the molecular basis of competence for chemical reprogramming, we compared polyadenylated transcriptomes of competent and noncompetent XX sperm-only mutants in the absence of the MEK inhibitor and hence in the absence of cell fate reprogramming. Despite their cellular production of sperm, competent mutants were enriched for oogenic messenger RNAs relative to mutants lacking competence for chemical reprogramming. In addition, competent mutants expressed the oocyte-specific protein RME-2, whereas those lacking competence did not. Therefore, mutants competent for reprogramming possess an intersexual molecular profile at both RNA and protein levels. We suggest that this intersexual molecular signature is diagnostic of an intermediate network state that poises the germline tissue for changing its cellular fate in response to environmental cues.

C. elegans: an invaluable model organism for the proteomics studies of the cholesterol-mediated signaling pathway

With the availability of its complete genome sequence and unique biological features relevant to human disease, Caenorhabditis elegans has become an invaluable model organism for the studies of proteomics, leading to the elucidation of nematode gene function. A journey from the genome to proteome of C. elegans may begin with preparation of expressed proteins, which enables a large-scale analysis of all possible proteins expressed under specific physiological conditions. Although various techniques have been used for proteomic analysis of C. elegans, systematic high-throughput analysis is still to come in order to accommodate studies of post-translational modification and quantitative analysis. Given that no integrated C. elegans protein expression database is available, it is about time that a global C. elegans proteome project is launched through which datasets of transcriptomes, protein-protein interaction and functional annotation can be integrated. As an initial target of a pilot project of the C. elegans proteome project, the cholesterol-mediated signaling pathway will be an excellent example since, like in other organisms, it is one of the key controlling pathways in cell growth and development in C. elegans. As this field tends to broaden to functional proteomics, there is a high demand to develop the versatile proteome informatics tools that can mange many different data in an integrative manner.

The C. elegans adult male germline: stem cells and sexual dimorphism

The hermaphrodite Caenorhabditis elegans germline has become a classic model for stem cell regulation, but the male C. elegans germline has been largely neglected. This work provides a cellular analysis of the adult C. elegans male germline, focusing on its predicted stem cell region in the distal gonad. The goals of this study were two-fold: to establish the C. elegans male germline as a stem cell model and to identify sex-specific traits of potential relevance to the sperm/oocyte decision. Our results support two major conclusions. First, adult males do indeed possess a population of germline stem cells (GSCs) with properties similar to those of hermaphrodite GSCs (lack of cell cycle quiescence and lack of reproducibly oriented divisions). Second, germ cells in the mitotic region, including those most distal within the niche, exhibit sex-specific behaviors (e.g. cell cycle length) and therefore have acquired sexual identity. Previous studies demonstrated that some germ cells are not committed to a sperm or oocyte cell fate, even in adults. We propose that germ cells can acquire sexual identity without being committed to a sperm or oocyte cell fate.

Sex and the single worm: sex determination in the nematode C. elegans

The study of sex determination in model organisms has been especially fruitful in increasing our understanding of developmental biology, gene regulation and evolutionary mechanisms. The free living nematode, Caenorhabditis elegans, can develop as one of two sexes; male or self-fertilizing hermaphrodite. Here we discuss the progress toward a genetic and molecular understanding of that decision. Numerous genetic loci have been identified that affect sexual fate, and epistasis analysis of these genes has led to a model of a regulatory hierarchy with stepwise negative interactions. It is becoming evident that many of the genes have numerous levels of regulation. We also discuss the apparent rapid rate of evolution that many of the sex determination proteins have undergone. Protein sequences of homologues from closely related species are more divergent than homologues of proteins involved in other developmental processes. Rapid evolution of sex determination genes may be a common theme throughout the animal kingdom.

Developmental genetics of Caenorhabditis elegans sex determination

The nematode Caenorhabditis elegans has two naturally occurring sexes: a self-fertile XX hermaphrodite that first produces sperm, then oocytes, and an XO male. The primary determinant of sex is the X:A ratio, the number of X chromosomes to sets of autosomes. The X:A ratio regulates not only sex determination, but also dosage compensation. In the intervening years since the identification of the X:A ratio, most of the key regulatory genes that respond to the X:A ratio have been genetically identified and ordered into regulatory hierarchies. Advances have also been made in identifying the X chromosome numerator elements of the X:A ratio. This review highlights the genetic, molecular, and biochemical approaches that have led to an understanding of how these genes interact to control sex determination and dosage compensation. The review also discusses the differences between the control of sexual cell fate in the soma and germ line of C. elegans and addresses the role of germ-line-specific regulation in controlling the sperm-oocyte decision in the hermaphrodite germ line. Finally, strategies that take advantage of the availability of the entire C. elegans genome sequence, which is expected to be completed in 1998, are discussed for identifying hitherto unidentified genes that may play a role in the control of sexual cell fate.

Vive la différence: males vs females in flies vs worms

For 600 million years, the two best-understood metazoan species, the nematode Caenorhabditis elegans and fruit fly Drosophila melanogaster, have developed independent strategies for solving a biological problem faced by essentially all metazoans: how to generate two sexes in the proper proportions. The genetic program for sexual dimorphism has been a major focus of research in these two organisms almost from the moment they were chosen for study, and it may now be the best-understood general aspect of their development. In this review, we compare and contrast the strategies used for sex determination (including dosage compensation) between "the fly" and "the worm" and the way this understanding has come about. Although no overlap has been found among the molecules used by flies and worms to achieve sex determination, striking similarities have been found in the genetic strategies used by these two species to differentiate their sexes.

Post-transcriptional regulation of sex determination in Caenorhabditis elegans: widespread expression of the sex-determining gene fem-1 in both sexes

The fem-1 gene of C. elegans is one of three genes required for all aspects of male development in the nematode. Current models of sex determination propose that the products of the fem genes act in a novel signal-transduction pathway and that their activity is regulated primarily at the post-translational level in somatic tissues. We analyzed the expression of fem-1 to determine whether it revealed any additional levels of regulation. Both XX hermaphrodites and XO males express fem-1 at approximately constant levels throughout development. Somatic tissues in hermaphrodites adopt female fates, but they nonetheless express fem-1 mRNA and FEM-1 protein, suggesting that the regulation of fem-1 activity is post-transcriptional and probably post-translational. A compact promoter directs functional expression of fem-1 transgenes, as assayed by their masculinizing activity in fem-1 mutants. Activity also requires any two or more introns, suggesting that splicing may enhance fem-1 expression. The minimal noncoding sequences required for activity of fem-1 transgenes suffice to direct expression of a fem-1::lacZ reporter gene in all somatic tissues in both sexes. Many fem-1 transgenes, including those that rescue male somatic development in fem-1 mutants, paradoxically feminize the germline. We suggest that they do so by interfering with the germline expression of the endogenous fem-1 gene.