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Fig. 4 | BMC Evolutionary Biology

Fig. 4

From: Tracing the evolution of the heterotrimeric G protein α subunit in Metazoa

Fig. 4

Evolution of the five families of Gα. a Summary of previous theories of Gα evolution without relative timelines [3, 6, 7, 9]. An ancestral GNA (α-white) underwent a series of duplications before diverging into three primary progenitor families. The progenitor GNAI/Q tandemly duplicated before undergoing a larger regional or chromosomal duplication. These gene pairs diverged into GNAI-like (blue) and GNAQ-like (orange) genes. GNAS (green), GNA12 (red), GNAQ’-GNAQ”, and GNAI’-GNAI” all duplicated to give rise to two copies from each parent. GNAI’-GNAI” duplicated into GNAO’-O″ (ultimately an alternatively spliced gene) and GNAI0-GNAT0 followed by two more duplications of GNAI0-GNAT0. GNAZ, a retrogene of GNAI0, was reinserted into the genome before the GNAI0-GNAT0 duplications. b New theory of Gα subfamily evolution incorporating current reports [1, 2, 4, 5, 10, 65, 68] with relative timelines included (not fit to scale). A single putative ancestral preGNA progenitor (α-white) duplicated into the preGNAI/Q progenitor and preGNAS. preGNAI/Q duplicated into two separate genes that diverged into preGNAI and preGNAQ. preGNAV arose from a duplication of preGNAI. preGNA12 is a retrogene, possibly of preGNAQ, though its precise origin is unclear. preGNAI later duplicated to give rise to preGNAO. Both preGNAI and preGNAQ underwent independent tandem duplication events before the 2R WGD. GNAS, GNA12 and GNAQ’-GNAQ” all retained two copies after the 2R WGD, while other hypothetical copies (not shown) were lost immediately after the 2R WGD and are not observed in any extant species. GNAI’-GNAI” retained three copies of this gene pair after the 2R WGD (GNAI4 remains only in lampreys). Other, lineage-specific deletions occurred for GNAV, GNAT3, GNAI4, and GNAT4 as described in the main text. GNAO gained alternative splicing of exons 7, 8 after 2R WGD (O.2.1). The retrogene GNAZ emerged in the Vertebrata lineage from a GNAI gene. Lineage-specific duplications and retrogenes are not included for clarity. Straight arrows depict duplications (local, tandem duplications, or WGD), curved arrows depict retrotranspositions. Curated preGNA- genes are denoted with “pre-” while “GNA” is removed for clarity in all paralogs. LCA = Last Common Ancestor

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