Singson A (2006) Curr Biol "Sperm activation: time and tide wait for no sperm."

Singson A

[Curr Biol, 2006]

Proper timing of sperm activation is required for reproductive success in Caenorhabditis elegans. The swm-1 gene encodes a predicted protease inhibitor that regulates sperm activation and the acquisition of amoeboid motility.

Singson A (2019) Mol Reprod Dev "Sydney Brenner: The birth of a model organism and the worm's connection to reproductive biology."

Singson A

[Mol Reprod Dev, 2019]

Singson, Andrew (2012) Worm Breeder's Gazette "Notable recent papers in reproductive biology"

Singson, Andrew

[Worm Breeder's Gazette, 2012]

Singson AW et al. (2001) Dev Biol "Every sperm is sacred: fertilization in Caenorhabditis elegans."

Singson AW, Singson A

[Dev Biol, 2001]

The nematode Caenorhabditis elegans is an attractive model system for the study of fertilization. C. elegans exists as a self-fertilizing hermaphrodite or as a male. This unusual situation provides an excellent opportunity to identify and maintain sterile mutants that affect sperm and no other cells. Analysis of these mutants can identify genes that encode proteins required for gamete recognition, adhesion, signaling, fusion, and/or activation at fertilization. These genes can also provide a starting point for the identification of additional molecules required for fertility. This review describes progress in the genetic and molecular dissection of fertilization in C. elegans and related studies on sperm competition.

Singson A et al. (2008) Int J Dev Biol "Genes required for the common miracle of fertilization in Caenorhabditis elegans."

Hang JS, Parry JM, Singson A

[Int J Dev Biol, 2008]

Fertilization involves multiple layers of sperm-egg interactions that lead to gamete fusion and egg activation. There must be specific molecules required for these interactions. The challenge is to determine the identity of the genes encoding these molecules and how their protein products function. The nematode worm Caenorhabditis elegans has emerged as an efficient model system for gene discovery and understanding the molecular mechanisms of fertilization. The primary advantage of the C. elegans system is the ability to isolate and maintain mutants that affect sperm or eggs and no other cells. In this review we describe progress and challenges in the analysis of genes required for gamete interactions and egg activation in the worm.

AW Singson et al. (1999) International C. elegans Meeting "A screen for extragenic suppressors of spe-9"

SW L'Hernault, AW Singson

[International C. elegans Meeting, 1999]

Mutations in the spe-9 gene lead to the production of sperm with wild type morphology and motility that cannot fertilize eggs even after contact between gametes. The spe-9 gene encodes a sperm transmembrane protein with an extracellular domain that contains ten epidermal growth factor (EGF)-like repeats. A common feature of proteins that include EGF-like motifs is their involvement in extracellular functions such as adhesive and ligand-receptor interactions. Additionally, the overall structure of the predicted SPE-9 protein is similar to that of ligands for the Notch/LIN-12/GLP-1 family of transmembrane receptors. We have designed a screen to identify the oocyte receptor for SPE-9 and other genes required for fertilization. There are several important features of this screen. First, we are screening for new mutations that restore fertility to spe-9 mutant worms. The restoration of self-fertility to self-sterile hermaphrodites is an extremely powerful selection tool. Second, the use of temperature sensitive alleles of spe-9 permit the culture and screening of very large numbers of worms, thus increasing the chance of isolating very rare mutations. Moreover, this approach should allow the recovery of mutations not obtainable by previous screening strategies. Finally, the use of specific alleles of spe-9 with point mutations in their extracellular domains will be more likely to detect compensatory mutations in the egg receptor for spe-9. We will report our latest progress with this screen.

Singson AW et al. (1999) Genetics "Sperm competition in the absence of fertilization in Caenorhabditis elegans."

L'Hernault SW, Singson AW, Hill KL

[Genetics, 1999]

Hermaphrodite self-fertilization is the primary mode of reproduction in the nematode Caenorhabditis elegans. However, when a hermaphrodite is crossed with a male, nearly all of the oocytes are fertilized by male-derived sperm. This sperm precedence during reproduction is due to the competitive superiority of male-derived sperm and results in a functional suppression of hermaphrodite self-fertility. In this study, mutant males that inseminate fertilization-defective sperm were used to reveal that sperm competition within a hermaphrodite does not require successful fertilization. However, sperm competition does require normal sperm motility. Additionally, sperm competition is not an absolute process because oocytes not fertilized by male-derived sperm can sometimes be fertilized by hermaphrodite-derived sperm. These results indicate that outcrossed progeny result from a wild-type cross because male-derived sperm are competitively superior and hermaphrodite-derived sperm become unavailable to oocytes. The sperm competition assays described in this study will be useful in further classifying the large number of currently identified mutations that alter sperm function and development in C. elegans.

Andrew Singson et al. (2007) International Worm Meeting "Genes required for gamete activation and fertilization."

Jean Parry, Rika Maruyama, Andrew Singson, Julie Hang

[International Worm Meeting, 2007]

Reproductive success requires that two haploid cells - sperm and egg - unite to form a diploid zygote. Despite being well described, the molecular underpinnings of fertilization are still poorly understood. We are addressing the molecular events required for reproductive success. The most significant advantage of C. elegans is the ability to isolate and maintain mutants that affect sperm or eggs and no other cells. We have focused on four classes of sterile mutants. The first class of mutants defines genes that are required for sperm activation (spermiogenesis mutants). The second class of mutants defines genes that are required by sperm to fertilize the egg (sperm function mutants). The third class of mutants defines genes required in the egg to be fertilized by sperm (egg function mutants). The last class of mutants is required in the egg to trigger development after fertilization (egg activation mutants). This work is providing us with a better understanding of the molecular mechanisms of fertilization in C. elegans. It also highlights many fundamental questions in cell biology and provides insights into the diversity of reproductive strategies.

Andrew Singson et al. (2002) West Coast Worm Meeting "Mutants that affect gamete function at fertilization"

Emily Putiri, Indrani Chatterjee, Pavan Kadandale, Brian Geldziler, Marty Nemeroff, Andrew Singson

[West Coast Worm Meeting, 2002]

The main goal of our lab is to understand the molecular mechanisms of fertilization. Initially, we have focused on the characterization of a group spe and fer genes required by sperm for fertilization. Although sterile, worms with these mutations produce morphologically wild-type sperm with normal motility that can come in contact with oocytes. Therefore mutations in these genes disrupt gamete recognition, adhesion, signaling and/or fusion. We have expanded our studies to include gene products required by the oocyte for fertilization. We are using RNAi to test candidate egg cell surface components for possible functions in fertilization. Additionally, we are conducting a genetic screen to identify conditional "egg sterile" mutants. We will report our progress on the genetic, phenotypic and molecular analysis of these genes. This work will lead to a better understanding of the specialized cell-cell interactions that occur at fertilization.

Singson AW et al. (1997) International C. elegans Meeting "Sperm Components Required for Sperm-Oocyte Interactions"

Mercer KB, L'Hernault SW, Singson AW

[International C. elegans Meeting, 1997]

The reproductive biology of the worm facilitates the identification of mutations that affect sperm and no other cells. This provides a unique opportunity to define sperm components required for sperm-oocyte interactions. Two interacting genes spe-9 and spe-13 produce cytologically normal and motile sperm that cannot fertilize oocytes even after contact. Therefore, these mutations disrupt either sperm-oocyte recognition, adhesion or fusion. Equivalent mutants have not been described in any other metazoan. We have isolated a 10 kb clone that fully rescues spe-9. This fragment overlaps the end of a cosmid clone that partially rescues spe-9. We analyzed the DNA sequence from this overlap with the Genemark program. The only predicted open reading frame in this region encodes a putative protein containing several cysteine-rich EGF-like repeats (CX4CX5CX8CXCX8CX6). Most notably, these repeats are seen in the extracellular domains of the LIN-12/GLP-1/Notch family of transmembrane receptors as well as in their ligands Delta, Serrate, Jagged, APX-1 and LAG-2. We are currently working to get more sequence from the rescuing fragments and to confirm that this ORF corresponds to spe-9. These results are consistent with the view that SPE-9 is involved in the specialized cell-cell interactions required for fertilization.