Genetic analysis of sterile mutants in the dpy-5 unc-13 (I) genomic region of Caenorhabditis elegans

Essential genes were identified in the 1.5-map unit dpy-5 unc-13 region of chromosome I in the Caenorhabditis elegans genome by rescuing lethal mutations using the duplication sDp2. In this paper, we report the mapping and complementation testing of lethal mutations, 45 of which identify 18 new, essential genes. This analysis brings the number of essential genes defined by the sDp2 rescue of lethal mutants to 97; 64 of these map between dpy-5 and unc-13. 61% of these essential genes are identified by more than one allele. Positioning of the mutations was done using the breakpoints of six duplications. The mutant phenotypes of 14 loci essential for fertility were characterized by Nomarski microscopy and DAPI staining. None of the mutants were rescued by wild-type male sperm. The cytological data showed that four genes produced mutants with defects in gonadogenesis, let-395, let-603, let-605 and let-610. Mutations in seven genes, let-355, let-367, let-384, let-513, let-544, let-545 and let-606, affected germ cell proliferation or gametogenesis. Mutants for the remaining three genes, let-370, let-599 and let-604, produced eggs that failed to develop or hatch, thereby acting as maternal effect lethals. We observed a nonrandom distribution of arrest phenotypes with regard to map position. Received: 8 May 1996 / Accepted : 27 January 1997     

Tests for parental imprinting in the nematode Caenorhabditis elegans

Summary The mutation him-6(e1423) leads to generalized chromosomal nondisjunction during meiosis in oogenesis and spermatogenesis of C. elegans. As a result, gametes nullisomic or disomic for each of the six chromosomes occur at appreciable frequency. Crosses utilizing marked him-6 strains were used to generate and identify exceptional euploid progeny which had received both homologues of a marked autosome either from the male parent or from the female parent. Examples of all ten possible exceptions were identified and found to be viable and fertile. These results (together with previous data for the X chromosome) indicate that major chromosomal imprinting effects do not occur during gametogenesis in this organism.     

The Caenorhabditis elegansRAD51 homolog is transcribed into two alternative mRNAs potentially encoding proteins of different sizes

In prokaryotes, the RecA protein plays a pivotal role in homologous recombination, catalyzing the transfer of a single DNA strand into an homologous molecule. Structural homologs of the bacterial RecA protein, called Rad51, have been found in different eukaryotes (from yeast to man), suggesting a certain level of conservation in recombination pathways among living organisms. We have cloned the homolog of RAD51 in Caenorhabditis elegans. The CeRAD51 gene is transcribed into two alternative mRNAs and potentially codes for two proteins of 395 and 357 amino acids in length, respectively. We discuss the evolutionary implications of these findings. Received: 26 May 1998 / Accepted: 18 August 1998     

Measuring the Effects of Bacteria on C. Elegans Behavior Using an Egg Retention Assay

C. elegans egg-laying behavior is affected by environmental cues such as osmolarity¹ and vibration². In the total absence of food C. elegans also cease egg-laying and retain fertilized eggs in their uterus³. However, the effect of different sources of food, especially pathogenic bacteria and particularly Enterococcus faecalis, on egg-laying behavior is not well characterized. The egg-in-worm (EIW) assay is a useful tool to quantify the effects of different types of bacteria, in this case E. faecalis, on egg- laying behavior.EIW assays involve counting the number of eggs retained in the uterus of C. elegans⁴. The EIW assay involves bleaching staged, gravid adult C. elegans to remove the cuticle and separate the retained eggs from the animal. Prior to bleaching, worms are exposed to bacteria (or any type of environmental cue) for a fixed period of time. After bleaching, one is very easily able to count the number of eggs retained inside the uterus of the worms. In this assay, a quantifiable increase in egg retention after E. faecalis exposure can be easily measured. The EIW assay is a behavioral assay that may be used to screen for potentially pathogenic bacteria or the presence of environmental toxins. In addition, the EIW assay may be a tool to screen for drugs that affect neurotransmitter signaling since egg-laying behavior is modulated by neurotransmitters such as serotonin and acetylcholine^5-9.     

Missing piece of top predator-based conservation: Demographic analysis of an owl population on a remote subtropical island

Top predators are frequently the target of conservation programs. Owls are such predators. However, previous studies of owls are biased to species occurring in temperate regions, whereas most owl species occur in tropical or subtropical regions and are understudied. Furthermore, owls are often endemic to islands and of unknown conservation status. Demographic data for such species are especially scarce although they are essential for initiating and promoting their conservation. As a case study of demographic analysis of owls in a tropical or subtropical area and on islands, we applied an integrated population model to 7-year monitoring data (2012–2018) of the Ryukyu Scops Owl population on Minami-daito Island, Japan. We used survival history data from 903 individuals, reproduction and sex ratio data from 213 broods, and count data of 2,526 individuals in total. Long-term averages of annual survival rates were 0.73 for adult females and 0.74 for adult males, although the sexual difference was not significant. Sex ratio estimates fluctuated annually and long-term averages were slightly skewed to males: 0.51 among fledglings, 0.54 among yearlings, and 0.52 among adults. Long-term averages of population size were estimated to be 273.4 females and 296.8 males. The long-term average of population growth rate was 0.98, suggesting a slightly declining trend. It was fortunate to recognize the declining trend during the early phase. Considering the general lack of fundamental ecological data on owls of tropical or subtropical areas and on islands, it seems likely that many endangered owl populations await conservation efforts.     

A Chemoreceptor That Detects Molecular Carbon Dioxide

Animals from diverse phyla possess neurons that are activated by the product of aerobic respiration, CO₂. It has long been thought that such neurons primarily detect the CO₂ metabolites protons and bicarbonate. We have determined the chemical tuning of isolated CO₂ chemosensory BAG neurons of the nematode Caenorhabditis elegans. We show that BAG neurons are principally tuned to detect molecular CO₂, although they can be activated by acid stimuli. One component of the BAG transduction pathway, the receptor-type guanylate cyclase GCY-9, suffices to confer cellular sensitivity to both molecular CO₂ and acid, indicating that it is a bifunctional chemoreceptor. We speculate that in other animals, receptors similarly capable of detecting molecular CO₂ might mediate effects of CO₂ on neural circuits and behavior.