Strongyloides spp. eliminate male-determining sperm post-meiotically

Area of Science:

• Parasitology
• Developmental Biology
• Genetics

Background:

• Normal male meiosis produces 50% nullo-X sperm, leading to male offspring.
• The parasitic nematodes Strongyloides spp. lack male offspring despite having XO males.
• Previous studies showed nullo-X sperm are absent or underrepresented in Strongyloides.

Purpose of the Study:

• Investigate the mechanism and timing of male-determining (nullo-X) sperm elimination in Strongyloides spp.
• Characterize spermatogenesis and the localization of key proteins in Strongyloides and Parastrongyloides trichosuri.

Main Methods:

• Differential interference contrast (DIC) microscopy.
• Immunohistochemistry.
• Fluorescent in situ hybridization (FISH).
• Quantitative whole genome sequencing.
• RNA interference (RNAi) for gene knockdown.

Main Results:

• Meiotic divisions in Strongyloides spp. and P. trichosuri produce expected numbers of X-bearing and nullo-X spermatocytes.
• Mature sperm in these species almost exclusively contain an X chromosome.
• Structures resembling C. elegans residual bodies, lacking DNA but containing sperm proteins like actin and major sperm protein (MSP), were observed.
• Knockdown of MSP impaired fertility in S. ratti.

Conclusions:

• Spermatocytes lacking an X chromosome likely undergo programmed cell death and form residual body-like structures.
• Major sperm protein (MSP) is crucial for fertility in Strongyloides ratti, similar to its role in C. elegans.
• The elimination of nullo-X sperm is a key factor in the absence of male offspring in Strongyloides spp.