The Caenorhabditis elegans gonad: a test tube for cell and developmental biology.

Sexual reproduction of multicellular organisms depends critically on the coordinate development of the germ line and somatic gonad, a process known as gonadogenesis. Together these tissues ensure the formation of functional gametes and, in the female of many species, create a context for production and further development of the zygote. Since the future of the species hangs in the balance, it is not surprising that gonadogenesis is a complex process involving conserved and multi-faceted developmental mechanisms. Genetic, anatomical, cell biological, and molecular experiments have established the nematode Caenorhabditis elegans as a paradigm for studying gonadogenesis. Furthermore, these studies demonstrate the utility of C. elegans gonadogenesis for exploring broad issues in cell and developmental biology, such as cell fate specification, morphogenesis, cell signaling, cell cycle control, and programmed cell death. The synergy of molecular genetics and cell biology conducted at single-cell resolution in real time permits an extraordinary depth of analysis in this organism. In this review, we first describe the embryonic and post-embryonic development and morphology of the C. elegans gonad. Next we recount seminal experiments that established the field, highlight recent results that provide insight into conserved developmental mechanisms, and present future prospects for the field.

Evidence for functional and physical association between Caenorhabditis elegans SEL-10, a Cdc4p-related protein, and SEL-12 presenilin.

Mutations in either of two human presenilin genes (PS1 and PS2) cause Alzheimer's disease. Here we describe genetic and physical interactions between Caenorhabditis elegans SEL-10, a member of the Cdc4p family of proteins, and SEL-12, a C. elegans presenilin. We show that loss of sel-10 activity can suppress the egg-laying defective phenotype associated with reducing sel-12 activity, and that SEL-10 can physically complex with SEL-12. Proteins of the Cdc4p family have been shown to target proteins for ubiquitin-mediated turnover. The functional and physical interaction between sel-10 and sel-12 therefore offers an approach to understanding how presenilin levels are normally regulated.

sel-10, a negative regulator of lin-12 activity in Caenorhabditis elegans, encodes a member of the CDC4 family of proteins.

Mutations that influence lin-12 activity in Caenorhabditis elegans may identify conserved factors that regulate the activity of lin-12/Notch proteins. We describe genetic evidence indicating that sel-10 is a negative regulator of lin-12/Notch-mediated signaling in C. elegans. Sequence analysis shows that SEL-10 is a member of the CDC4 family of proteins and has a potential human ortholog. Coimmunoprecipitation data indicate that C. elegans SEL-10 complexes with LIN-12 and with murine Notch4. We propose that SEL-10 promotes the ubiquitin-mediated turnover of LIN-12/Notch proteins, and discuss potential roles for the regulation of lin-12/Notch activity by sel-10 in cell fate decisions and tumorigenesis.

Evidence for physical and functional association between EMB-5 and LIN-12 in Caenorhabditis elegans.

The Caenorhabditis elegans LIN-12 and GLP-1 proteins are members of the LIN-12/Notch family of receptors for intercellular signals that specify cell fate. Evidence presented here suggests that the intracellular domains of LIN-12 and GLP-1 interact with the C. elegans EMB-5 protein and that the emb-5 gene functions in the same pathway as the lin-12 and glp-1 genes. EMB-5 is similar in sequence to a yeast protein that controls chromatin structure. Hence, a direct consequence of LIN-12 or GLP-1 activation may be an alteration of chromatin structure that produces changes in transcriptional activity.

Prescribing patterns of antilipemic drugs and prevalence of hypercholesterolemia in the Nova Scotia population more than 65 years old.

OBJECTIVE: To examine the prevalence of antilipemic drug use, demographic characteristics of patients using these drugs, and the prevalence of hypercholesterolemia in the Nova Scotia population over 65 years of age. DESIGN: Information was collected on the prescribing of antilipemic drugs using Nova Scotia Medical Services Insurance Pharmacare program data from October 1991 through March 1992. Pharmacare data were compared with prevalence data on increased low-density lipoprotein (LDL) cholesterol concentrations obtained from the Nova Scotia Heart Health Survey (NSHHS). SETTING: Pharmacare is a centrally administered drug insurance system maintained in computerized claims files since 1974. It provides prescription drugs to all residents of Nova Scotia who are at least 65 years old and who are insured under the provincial Medicare program. PARTICIPANTS: In the 1991-1992 fiscal year, 47,000 men and 65,700 women were eligible for Pharmacare. The NSHHS was administered to a probability sample of 2,108 individuals, representative of the 1986 population aged 18-74 years. MAIN OUTCOME MEASURES: Prescriptions for antilipemic agents. RESULTS: The NSHHS data indicated that 3.7% of women and 2.3% of men at least 65 years old and 4.8% of women and 2.8% of men 65-74 years old received a prescription for antilipemic drugs.

Dosage-dependent modulation of glucose repression by MSN3 (STD1) in Saccharomyces cerevisiae.

The SNF1 protein kinase of Saccharomyces cerevisiae is required to relieve glucose repression of transcription. To identify components of the SNF1 pathway, we isolated multicopy suppressors of defects caused by loss of SNF4, an activator of the SNF1 kinase. Increased dosage of the MSN3 gene restored invertase expression in snf4 mutants and also relieved glucose repression in the wild type. Deletion of MSN3 caused no substantial phenotype, and we identified a homolog, MTH1, encoding a protein 61% identical to MSN3. Both are also homologous to chicken fimbrin, human plastin, and yeast SAC6 over a 43-residue region. Deletion of MSN3 and MTH1 together impaired derepression of invertase in response to glucose limitation. Finally, MSN3 physically interacts with the SNF1 protein kinase, as assayed by a two-hybrid system and by in vitro binding studies. MSN3 is the same gene as STD1, a multicopy suppressor of defects caused by overexpression of the C terminus of TATA-binding protein (R. W. Ganster, W. Shen, and M. C. Schmidt, Mol. Cell. Biol. 13:3650-3659, 1993). Taken together, these data suggest that MSN3 modulates the regulatory response to glucose and may couple the SNF1 pathway to transcription.

A protein kinase substrate identified by the two-hybrid system.

A genetic method, the two-hybrid system, was used to identify four genes encoding proteins that interact with the SNF1 protein kinase from yeast. One of the genes, SIP1, was independently isolated as a multicopy suppressor of defects caused by reduced SNF1 kinase activity, and genetic evidence supports its function in the SNF1 pathway. The SIP1 protein co-immunoprecipitated with SNF1 and was phosphorylated in vitro. Thus, the two-hybrid system, which is applicable to any cloned gene, can be used to detect physical interactions between protein kinases and functionally related substrate proteins.

Relationship of the cAMP-dependent protein kinase pathway to the SNF1 protein kinase and invertase expression in Saccharomyces cerevisiae.

The SNF1 protein kinase and the associated SNF4 protein are required for release of glucose repression in Saccharomyces cerevisiae. To identify functionally related proteins, we selected genes that in multicopy suppress the raffinose growth defect of snf4 mutants. Among the nine genes recovered were two genes from the cAMP-dependent protein kinase (cAPK) pathway, MSI1 and PDE2. Increased dosage of these genes partially compensates for defects in nutrient utilization and sporulation in snf1 and snf4 null mutants, but does not restore invertase expression. These results suggest that SNF1 and cAPK affect some of the same cellular responses to nutrients. To examine the role of the cAPK pathway in regulation of invertase, we assayed mutants in which the cAPK is not modulated by cAMP. Expression of invertase was regulated in response to glucose and was dependent on SNF1 function. Thus, a cAMP-responsive cAPK is dispensable for regulation of invertase.

Yeast casein kinase I homologues: an essential gene pair.

We report the isolation of an essential pair of Saccharomyces cerevisiae genes that encode protein kinase homologues. The two genes were independently isolated as dosage-dependent suppressors. Increased dosage of YCK1 suppressed defects caused by reduced SNF1 protein kinase activity, and increased dosage of YCK2 relieved sensitivity of wild-type cells to salt stress. The two genes function identically in the two growth assays, and loss of function of either gene alone has no discernible effect on growth. However, loss of function of both genes results in inviability. The two predicted protein products share 77% overall amino acid identity and contain sequence elements conserved among protein kinases. Partial sequence obtained for rabbit casein kinase I shares 64% identity with the two yeast gene products. Moreover, an increase in casein kinase I activity is observed in extracts from cells overexpressing YCK2. Thus YCK1 and YCK2 appear to encode casein kinase I homologues.

Assessing potential predisposition of elementary school children to heart disease.

Physical well-being has been designated a top priority for the children in the Clovis (California) Unified School District. In an effort to diminish coronary risk factors and encourage a healthy life style, a health assessment battery was developed for students in grades 1 through 6. The battery included measurements in height, weight, blood pressure, sit and reach flexibility, and skin-fold test for body fat composition. More than 5000 students were administered the tests by a health assessment team consisting of two nurses, three physical education resource teachers, and two clerical staff members. A random sample of 100 males and 100 females at each grade level was utilized for the statistical analysis. The correlation between body fat and weight was .80 (p v .05) in the fifth and sixth grades. Body fat was positively correlated with both systolic and diastolic measures of blood pressure. The coefficient averaged .21 (p v .05) over the 6 grades for systolic and .22 (p .05) over the 6 grades for diastolic blood pressure. Future plans call for the development of a longitudinal profile of students, as well as establishing district norms for the test battery.