Monotreme-specific conserved putative proteins derived from retroviral reverse transcriptase.

Area of Science:

• Evolutionary Biology
• Genomics
• Mammalian Evolution

Background:

• Endogenous retroviruses (ERVs) have significantly influenced mammalian evolution, with ERV-derived genes identified in therians, often linked to placental development.
• The role and origin of ERV-derived genes in monotremes, an evolutionarily distinct group of oviparous mammals, remain largely unexplored.

Purpose of the Study:

• To identify and characterize endogenous retrovirus (ERV)-derived genes in monotremes (platypus and echidna).
• To investigate the evolutionary conservation and expression patterns of these novel genes.

Main Methods:

• Comprehensive genomic search for ERV-derived genes in platypus and echidna.
• Comparative genomic analyses to assess conservation and selection pressures.
• Transcript expression analysis using RT-PCR or similar methods.

Main Results:

• Identification of three novel reverse transcriptase-like genes (RTOM1, RTOM2, RTOM3) within the GRIP2 intron of monotremes.
• Demonstration of strong conservation and purifying selection acting on RTOM1-3 between platypus and echidna.
• Specific expression of all RTOM transcripts detected exclusively in the testis.

Conclusions:

• This study reports the first monotreme-specific de novo gene candidates originating from ERVs.
• The findings suggest RTOM genes may have arisen from tandem duplications prior to monotreme divergence.
• The testis-specific expression points to a potential physiological role for these ERV-derived genes in monotremes, offering unique evolutionary insights.