Indrani Chatterjee

The Caenorhabditis elegans spe-38 gene encodes a novel four-pass integral membrane protein required for sperm function at fertilization

A mutation in the Caenorhabditis elegans spe-38 gene results in a sperm-specific fertility defect. spe-38 sperm are indistinguishable from wild-type sperm with regards to their morphology, motility and migratory behavior. spe-38 sperm make close contact with oocytes but fail to fertilize them. spe-38 sperm can also stimulate ovulation and engage in sperm competition. The spe-38 gene is predicted to encode a novel four-pass (tetraspan) integral membrane protein. Structurally similar tetraspan molecules have been implicated in processes such as gamete adhesion/fusion in mammals, membrane adhesion/fusion during yeast mating, and the formation/function of tight-junctions in metazoa. In antibody localization experiments, SPE-38 was found to concentrate on the pseudopod of mature sperm, consistent with it playing a direct role in gamete interactions.

The sperm surface localization of the TRP-3/SPE-41 Ca2+ -permeable channel depends on SPE-38 function in Caenorhabditis elegans.

Despite undergoing normal development and acquiring normal morphology and motility, mutations in spe-38 or trp-3/spe-41 cause identical phenotypes in Caenorhabditis elegans-mutant sperm fail to fertilize oocytes despite direct contact. SPE-38 is a novel, four-pass transmembrane protein and TRP-3/SPE-41 is a Ca(2+)-permeable channel. Localization of both of these proteins is confined to the membranous organelles (MOs) in undifferentiated spermatids. In mature spermatozoa, SPE-38 is localized to the pseudopod and TRP-3/SPE-41 is localized to the whole plasma membrane. Here we show that the dynamic redistribution of TRP-3/SPE-41 from MOs to the plasma membrane is dependent on SPE-38. In spe-38 mutant spermatozoa, TRP-3/SPE-41 is trapped within the MOs and fails to reach the cell surface despite MO fusion with the plasma membrane. Split-ubiquitin yeast-two-hybrid analyses revealed that the cell surface localization of TRP-3/SPE-41 is likely regulated by SPE-38 through a direct protein-protein interaction mechanism. We have identified sequences that influence the physical interaction between SPE-38 and TRP-3/SPE-41, and show that these sequences in SPE-38 are required for fertility in transgenic animals. Despite the mislocalization of TRP-3/SPE-41 in spe-38 mutant spermatozoa, ionomycin or thapsigargin induced influx of Ca(2+) remains unperturbed. This work reveals a new paradigm for the regulated surface localization of a Ca(2+)-permeable channel.

A comparative study of sperm morphology, cytology and activation in Caenorhabditis elegans , Caenorhabditis remanei and Caenorhabditis briggsae

Studies of sterile mutants in Caenorhabditis elegans have uncovered new insights into fundamental aspects of gamete cell biology, development, and function at fertilization. The genome sequences of C. elegans, Caenorhabditis briggsae and Caenorhabditis remanei allow for informative comparative studies among these three species. Towards that end, we have examined wild-type sperm morphology and activation (spermiogenesis) in each. Light and electron microscopy studies reveal that general sperm morphology, organization, and ultrastructure are similar in all three species, and activation techniques developed for C. elegans were found to work well in both C. briggsae and C. remanei. Despite important differences in the reproductive mode between C. remanei and the other two species, most genes required for spermiogenesis are conserved in all three. Finally, we have also examined the subcellular distribution of sperm epitopes in C. briggsae and C. remanei that cross-react with anti-sera directed against C. elegans sperm proteins. The baseline data in this study will prove useful for the future analysis and interpretation of sperm gene function across nematode species.

Germline transformation of Caenorhabditis elegans by injection

Microinjection is a commonly used technique for DNA transformation in Caenorhabditis elegans. It is a powerful tool that links genetic and molecular analysis to phenotypic analysis. In this chapter we shall provide an overview of microinjection for germline transformation in worms. Our discussion will emphasize C. elegans reproductive biology, applications and protocols for carrying out microinjection in order to successfully obtain transgenic worms.

Dramatic fertility decline in aging C. elegans males is associated with mating execution deficits rather than diminished sperm quality.

Although much is known about female reproductive aging, fairly little is known about the causes of male reproductive senescence. We developed a method that facilitates culture maintenance of Caenorhabditis elegans adult males, which enabled us to measure male fertility as populations age, without profound loss of males from the growth plate. We find that the ability of males to sire progeny declines rapidly in the first half of adult lifespan and we examined potential factors that contribute towards reproductive success, including physical vigor, sperm quality, mating apparatus morphology, and mating ability. Of these, we find little evidence of general physical decline in males or changes in sperm number, morphology, or capacity for activation, at time points when reproductive senescence is markedly evident. Rather, it is the loss of efficient mating ability that correlates most strongly with reproductive senescence. Low insulin signaling can extend male ability to sire progeny later in life, although insulin impact on individual facets of mating behavior is complex. Overall, we suggest that combined modest deficits, predominantly affecting the complex mating behavior rather than sperm quality, sum up to block effective C. elegans male reproduction in middle adult life.

DHS-21, a dicarbonyl/l-xylulose reductase (DCXR) ortholog, regulates longevity and reproduction in Caenorhabditis elegans

Dicarbonyl/l‐xylulose reductase (DCXR) converts l‐xylulose into xylitol, and reduces various α‐dicarbonyl compounds, thus performing a dual role in carbohydrate metabolism and detoxification. In this study, we identified DHS‐21 as the only DCXR ortholog in Caenorhabditis elegans. The dhs‐21 gene is expressed in various tissues including the intestine, gonadal sheath cells, uterine seam (utse) cells, the spermathecal‐uterus (sp‐ut) valve and on the plasma membrane of spermatids. Recombinant DHS‐21 was shown to convert l‐xylulose to xylitol using NADPH as a cofactor. Dhs‐21 null mutants of C. elegans show defects in longevity, reproduction and egg‐laying. Knock‐down of daf‐16 and elt‐2 transcription factors affected dhs‐21 expression. These results suggest that DHS‐21 is a bona fide DCXR of C. elegans, essential for normal life span and reproduction.

Tracking ‘Same–Sex Love’ from Antiquity to the Present in South Asia

This essay focuses on the anthology Same–Sex Love in India: Readings from Literature and History (2000), edited by Ruth Vanita and Saleem Kidwai. Unlike many other recently published, celebratory ‘gay anthologies’, this book contributes to ongoing scholarly work on specific same–sex erotic practices and relations in historical and cultural context. We examine issues relevant to this anthology and other such projects: the use of ‘love’ and ‘same–sex’ as (stable) signifiers over centuries; the validity of interpreting social reality through literary texts from the period; the difficulties of locating ‘love’ in severely hierarchical, even slave–owning, societies; and the implications of using such anthologies in the classroom.

Meiotic diapause: how a sperm signal sets you free.

Major sperm protein, a cytoskeletal molecule required for the amoeboid motility of sperm in Caenorhabditis elegans, also functions as a signaling molecule that regulates the rates of meiotic maturation and ovulation. Recent work has begun to uncover new genes required for the response to this signal in both somatic and germ line cells.