Evolution of a New Testis-Specific Functional Promoter Within the Highly Conserved Map2k7 Gene of the Mouse.

Tobias Heinen,Chen Xie,Sven Künzel,Diethard Tautz,Maryam Keshavarz,Dominik Stappert

doi:10.3389/fgene.2021.812139

Abstract

Map2k7 (synonym Mkk7) is a conserved regulatory kinase gene and a central component of the JNK signaling cascade with key functions during cellular differentiation. It shows complex transcription patterns, and different transcript isoforms are known in the mouse (Mus musculus). We have previously identified a newly evolved testis-specific transcript for the Map2k7 gene in the subspecies M. m. domesticus. Here, we identify the new promoter that drives this transcript and find that it codes for an open reading frame (ORF) of 50 amino acids. The new promoter was gained in the stem lineage of closely related mouse species but was secondarily lost in the subspecies M. m. musculus and M. m. castaneus. A single mutation can be correlated with its transcriptional activity in M. m. domesticus, and cell culture assays demonstrate the capability of this mutation to drive expression. A mouse knockout line in which the promoter region of the new transcript is deleted reveals a functional contribution of the newly evolved promoter to sperm motility and the spermatid transcriptome. Our data show that a new functional transcript (and possibly protein) can evolve within an otherwise highly conserved gene, supporting the notion of regulatory changes contributing to the emergence of evolutionary novelties.

Highlights

Mitogen activated protein kinase (MAPK) pathways are highly conserved throughout eukaryotes and trigger multistep signaling cascades mediating transcriptional response upon receiving outside stimuli (English et al, 1999; Chang and Karin, 2001)
We included in our analysis testis samples from the inbred strain C57Bl6/J [derived from M. m. domesticus (Frazer et al, 2007)], as well as from wild-caught mice that were kept under outbreeding conditions (Harr et al, 2016)
To assess the stage of spermatid development at which Map2k7 is expressed, we used in situ hybridization on testis sections from M. m. domesticus and M. m. musculus

Summary

Introduction

Mitogen activated protein kinase (MAPK) pathways are highly conserved throughout eukaryotes and trigger multistep signaling cascades mediating transcriptional response upon receiving outside stimuli (English et al, 1999; Chang and Karin, 2001). The JNK pathway has several known functions in the immune system, apoptosis, and developmental processes (Sabapathy et al, 1999; Dong et al, 2000; Nishina et al, 2004; Wada et al, 2004; Wang et al, 2007). Knock out of both JNK1 and JNK2 (double KO) or of Mapk2k7 alone, leads to embryonic lethality in mice (Wang et al, 2007)

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Conclusion