Expansion of transducin subunit gene families in early vertebrate tetraploidizations

Abstract

Hundreds of gene families expanded in the early vertebrate tetraploidizations including many gene families in the phototransduction cascade. We have investigated the evolution of the heterotrimeric G-proteins of photoreceptors, the transducins, in relation to these events using both phylogenetic analyses and synteny comparisons. Three alpha subunit genes were identified in amniotes and the coelacanth, GNAT1-3; two of these were identified in amphibians and teleost fish, GNAT1 and GNAT2. Most tetrapods have four beta genes, GNB1-4, and teleosts have additional duplicates. Finally, three gamma genes were identified in mammals, GNGT1, GNG11 and GNGT2. Of these, GNGT1 and GNGT2 were found in the other vertebrates. In frog and zebrafish additional duplicates of GNGT2 were identified. Our analyses show all three transducin families expanded during the early vertebrate tetraploidizations and the beta and gamma families gained additional copies in the teleost-specific genome duplication. This suggests that the tetraploidizations contributed to visual specialisations.

Evolutionary hierarchy of vertebrate-like heterotrimeric G protein families

“…However, searches in species that evolved before the divergence of tunicates were unfruitful. These findings are consistent with previous studies (Lagman et al, 2012) and illustrate that the Gc gene repertoire is limited only to GNG-and GNG13-like genes in most analyzed metazoans that evolved before the divergence of deuterostomes. Later, the GNG gene cluster and the ancestral gene of the transducin family likely expanded in the two genome doublings, i.e.…”

“…S4b). Although, phylogenetic trees lacked high confidence support, the finding that bilaterian invertebrate sequences are more GNAI-like is strongly supported by previous studies that demonstrated the transducins (GNAT family belonging to Gai/o class) likely evolved at the early origins of vertebrates and are involved in phototransduction in the rod and cone photoreceptor cells of the vertebrate retina (Lagman et al, 2012;Lamb, 2009;Larhammar et al, 2009;Lin et al, 2013). Furthermore, our phylogenetic analysis also shows that GNAO-like amino acid sequences are found in almost all analyzed metazoans.…”

“…These events gave rise to the expansion of several gene families including the heterotrimeric G proteins. Previously, several studies addressed the evolution of G protein families including the GNAI/GNAT, GNB1-4 paralogon and G gamma transducins (GNAT1/GNAT2/GNA11) in the early origins of vertebrates (Downes and Gautam, 1999;Hurowitz et al, 2000;Lagman et al, 2012;Wilkie et al, 1992). Here, we significantly broaden the perspective by including other subunit families, such as GNAS/L, GNAQ/11, GNA12/13, as well as the GNG cluster (Fig.…”

Why coelacanths are not ‘living fossils’

“…In addition, most phylogenetic analyses -including analysis of Hox sequences [23][24][25][26] -do not support the hypothesis that the Latimeria genome is slow evolving, i.e. they do not place coelacanth sequences on short branches nor do they detect low substitution rates [24,[27][28][29][30][31]. The clearest example, which involves the largest number of genes, is a phylogeny based study of forty-four nuclear genes that does not show a dramatic decrease, if any, in the rate of molecular evolution in the coelacanth lineage [32].…”

The Nordic Countries Meeting on the Zebrafish as a Model for Development and Disease 2012

“…4 Another presentation reported on studies of the evolution of visual opsin genes in relation to early vertebrate tetraploidizations in a manner similar to what has been done for other gene families in the phototransduction cascade. 5 Two new techniques were presented: (i) live tracing of cell lineages using a Cre-reporter line with improved optical properties (contact person: Bettina Ryll at bettina .ryll@ebc.uu.se) and (ii) a rapid whole mount in situ and immuno-hybridization technique to be used in automated screens (contact person: Nina Kaukua at nina.kaukua@ki.se).…”