Sexual dimorphism in the tardigrade Paramacrobiotus metropolitanus transcriptome

Area of Science:

• Zoology and Genetics
• Comparative Genomics
• Evolutionary Biology

Background:

• Sexual dimorphism is common in gonochoristic animals, driven by sex determination pathways.
• The Doublesex-Mab-3-Related Transcription factor (DMRT) is a conserved regulator of sexual differentiation across taxa.
• Tardigrades display significant sexual dimorphism, yet the genetic basis remains largely unexplored.

Purpose of the Study:

• To investigate the molecular basis of sexual dimorphism in the tardigrade species Paramacrobiotus metropolitanus.
• To identify sex-specific genomic and transcriptomic differences between male and female tardigrades.

Main Methods:

• Omics analyses, including transcriptome sequencing, were performed on sex-identified specimens.
• Phylogenetic analysis was used to trace the evolutionary history of key sex determination genes.
• Differential gene expression analysis identified male-biased genes and genomic loci.

Main Results:

• Approximately 2,000 male-biased genes were identified, originating from 29 non-sex-specific genomic loci.
• Two Macrobiotidae family-specific DMRT paralogs were significantly upregulated in males.
• No genomic differences were found between sexes, and the doublesex ortholog is absent in tardigrades, suggesting its post-Tardigrada divergence.

Conclusions:

• This study provides a foundational understanding of the genetic differences and sex determination cascade in tardigrades.
• The identification of male-biased DMRT subfamily and male-biased genomic loci offers insights into tardigrade sex determination.
• Sex-biased expression of anhydrobiosis genes suggests a role in protecting sex-specific tissues and gametes during extreme stress.