Quantifying Embryonic Lethality Rate in Caenorhabditis elegans

Summary

This protocol provides a simple, low-cost procedure to quantify the rate of embryonic lethality in Caenorhabditis elegans. It enables straightforward detection of embryonic abnormalities across populations without specialized equipment or worm-picking expertise. The protocol can be used to quantify the effects of genetic mutations, RNA interference-mediated gene knockdowns, and diet.

Abstract

Embryonic lethality is a cornerstone phenotype used in Caenorhabditis elegans research to characterize developmental defects arising from factors such as toxic exposures and genetic mutations. Therefore, accurately quantifying the penetrance of embryonic lethality is critical for understanding the mechanisms and impact of these perturbations on animal development. Although automated scoring platforms exist, these approaches often require substantial financial investment and specialized hardware or software. This article describes a low-tech, low-cost assay that quantifies embryonic lethality by measuring the percentage of embryos that successfully fail to hatch. Notably, this version of the assay eliminates the need for a worm pick, making it exceptionally suitable for beginners. An additional advantage of this approach is that each technical replicate assays progeny from multiple animals, avoiding the potential biases of single-worm assays. This protocol includes a discussion of critical parameters, such as the minimum number of progeny required to accurately capture phenotype penetrance and the rationale for the methodology. Finally, we provide guidance on adapting the assay to assess the effects of gene knockdown via RNA interference, pharmacological treatments, or nutritional supplementation, adding a versatile and accessible tool to the toolkit of C. elegans researchers.

Introduction

Embryonic lethality is a critical phenotype for assessing the roles of genes and environmental factors in early development. C. elegans is a powerful model for studying developmental processes because of its invariant cell lineage, transparent body, and rapid life cycle¹. C. elegans embryonic lethality can be used to assess developmental integrity under chemical, pharmacological, nutritional, and genetic perturbations^2,3,4,5. Therefore, accessible and versatile methods for accurately quantifying embr....

Protocol

1. C. elegans maintenance

NOTE: Detailed guidance on C. elegans husbandry can be found in WormBook¹¹.

1. Prepare maintenance Nematode Growth Medium (NGM) plates.
   1. To make 1 L of NGM, combine 3 g NaCl, 2.5 g bacteriological peptone, and 17 g agar in a 2 L bottle. Add 975 mL of distilled water and a stir bar, then autoclave for 20 min at 121 °C.
   2. Allow the medium to cool to 55 °C in a water bath. Place the bottle on a stir plate and, using aseptic technique, add 25 mL of 1 M potassium phosphate buffer and 1 mL each of the following: 1 M MgSO₄, ....

Results

The embryonic lethality assay was performed in two strains: wild-type N2 and the RNAi-hypersensitive strain rrf-3(pk1426). Using RNAi by feeding, we knocked down genes previously reported to cause embryonic lethality in high-throughput screens^9,12. Figure 2 provides a representative demonstration of assay performance. T04G9.4 knockdown produced nearly fully penetrant embryonic lethality in both rrf-3(pk1426) and N2 .......

Discussion

Several steps are critical for assay reproducibility and accuracy. First, the bleaching step must be carefully timed to dissolve adult worms without damaging the embryos. Another important point is transferring a sufficient number of embryos for counting: too few will reduce the precision, whereas too many will make counting unnecessarily tedious. Next, embryo transfer should be performed before the embryos begin hatching. Otherwise, hatchlings will be washed away together with adults, which can skew hatching rates towar.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Ampicillin sodium salt	Sigma-Aldrich	A9518
Bacteriological peptone	Fischer Scientific	DF0118-17-0
C. elegans N2	Caenorhabditis Genetics Center	N2	wild type
C. elegans NL2099	Caenorhabditis Genetics Center	NL2099	rrf-3(pk1426) II. RNAi hypersensitive
Calcium chloride, anhydrous	Sigma-Aldrich	746495
Cholesterol	Sigma-Aldrich	C3045
Conical tubes, 15 mL	VWR	60818-725
Culture tubes, 14 mL	VWR	470150-966
Diaphragm vacuum pump	Amazon	TC-100
Dissecting microscope	AmScope	SM-2
Escherichia coli HT115	Caenorhabditis Genetics Center		RNAse III-deficient, used for RNAi by feeding experiments
Escherichia coli OP50	Caenorhabditis Genetics Center
Granulated agar	Fischer Scientific	BP97445
Handheld tally counter	LabDepot	HTCP01
IPTG, dioxane free (Isopropyl-b-D-thiogalactoside)	US Biological	I8500
LB Broth (Miller)	US Biological	L1520	To make LB medium dissolve 25 g of LB powder in 1 L of distilled water. Autoclave for 20 min at 121.1 °C.
Luer Lok disposable syringe	BH Supplies	BH20LL
Magnesium sulfate	Sigma-Aldrich	M2643
Microscopy slides	Sail Brand	7101
Petri dishes, 100 mm	Tritech Research	T3371
Petri dishes, 35 mm	Tritech Research	T3501
Potassium Phosphate Buffer (PPB)			To make potassium phosphate buffer (1 M), dissolve 98 g of potassium phosphate monobasic and 48 g of potassium phosphate dibasic in 1 L of distilled water. Adjust the pH to 6. Autoclave for 20 min at 121 °C.
Potassium phosphate dibasic	Sigma-Aldrich	795496
Potassium phosphate monobasic	Sigma-Aldrich	529568
Rocker (nutating mixer)	Corning LSE	6720
Serological pipettes, 25 mL	Corning	4489
Serological pipettes, 5 mL	Celltreat	229235
Shaking incubator Infors Multitron	INFORS HT	NA
Sodium chloride	Sigma-Aldrich	S9888
Sodium hydroxide solution, 5 N	Fisher Scientific	SS256-500
Sodium hypochlorite, 5%	LabDepot	LC246302
Sodium phosphate dibasic	Sigma-Aldrich	S9763
Sorvall ST1 Plus Centrifuge	Thermo Scientific	75016030
Stir plate	ONilab	ONi28-S
Syringe filters	Semmerfeld	JQP033022QE1
Water bath	FOUR E's Scientific	WB401