Gene Loss

Publication Details

Identifier: JB_METKVV

Curator: M. Lopes-Marques

DOI: 10.1016/j.ympev.2017.01.020

PMID: 28193458

Title:

Inactivation of the olfactory marker protein (OMP) gene in river dolphins and other odontocete cetaceans.

Abstract:

Various toothed whales (Odontoceti) are unique among mammals in lacking olfactory bulbs as adults and are thought to be anosmic (lacking the olfactory sense). At the molecular level, toothed whales have high percentages of pseudogenic olfactory receptor genes, but species that have been investigated to date retain an intact copy of the olfactory marker protein gene (OMP), which is highly expressed in olfactory receptor neurons and may regulate the temporal resolution of olfactory responses. One hypothesis for the retention of intact OMP in diverse odontocete lineages is that this gene is pleiotropic with additional functions that are unrelated to olfaction. Recent expression studies provide some support for this hypothesis. Here, we report OMP sequences for representatives of all extant cetacean families and provide the first molecular evidence for inactivation of this gene in vertebrates. Specifically, OMP exhibits independent inactivating mutations in six different odontocete lineages: four river dolphin genera (Platanista, Lipotes, Pontoporia, Inia), sperm whale (Physeter), and harbor porpoise (Phocoena). These results suggest that the only essential role of OMP that is maintained by natural selection is in olfaction, although a non-olfactory role for OMP cannot be ruled out for lineages that retain an intact copy of this gene. Available genome sequences from cetaceans and close outgroups provide evidence of inactivating mutations in two additional genes (CNGA2, CNGA4), which imply further pseudogenization events in the olfactory cascade of odontocetes. Selection analyses demonstrate that evolutionary constraints on all three genes (OMP, CNGA2, CNGA4) have been greatly reduced in Odontoceti, but retain a signature of purifying selection on the stem Cetacea branch and in Mysticeti (baleen whales). This pattern is compatible with the 'echolocation-priority' hypothesis for the evolution of OMP, which posits that negative selection was maintained in the common ancestor of Cetacea and was not relaxed significantly until the evolution of echolocation in Odontoceti.

Last update:

25-11-2024

Associated Glosses (12 results)

GlossID	Species	Symbol	Gene Loss Mechanism	Loss Type	Lineage Specific	Citation
GL_WDSMVC	Tursiops truncatus	CNGA4	LOF (frameshift, premature stop, ss)	Full	No	10.1016/j.ympev.2017.01.020
GL_Z4RCOC	Lipotes vexillifer	CNGA4	LOF (frameshift, premature stop, ss)	Full	No	10.1016/j.ympev.2017.01.020