Olivares-Costa, M. | Search bioRxiv

bioRxiv2024

Evolutionary and Functional Analysis of Monoamine Oxidase C (MAO C): A Novel Member of the MAO Gene Family

The monoamine oxidase (MAO) gene family encodes for enzymes that perform the oxidative deamination of monoamines, a process required to degrade norepinephrine, serotonin, dopamine, and other amines. While mammalian MAO enzymes, MAO A and MAO B, have been extensively studied, the molecular properties of the other family members are only partly uncovered. This study aims to explore the evolution of monoamine oxidases, emphasizing understanding the MAO gene repertoire among vertebrates. Our analyses show that the duplication that gave rise to MAO A and MAO B occurred in the ancestor of tetrapods, between 408 and 352 million years ago. Non-tetrapod jawed vertebrates possess the ancestral preduplicative condition of MAO A/B. Our results also identified a new family member, MAO C, in non-tetrapod jawed vertebrates. Thus, most jawed vertebrates possess a repertoire of two MAO genes, MAO A and MAO B in tetrapods and MAO A/B and MAO C in non-tetrapod jawed vertebrates, representing different MAO gene lineages. Jawless vertebrates possess the ancestral condition of a single copy gene, MAO A/B/C. Enzymatic assays conducted on the MAO recombinant enzymes of the Indo-Pacific tarpon show that both proteins, MAO A/B and MAO C, have enzymatic and molecular properties more similar to human MAO A, with the former featuring a strikingly higher activity rate when compared to all other MAO enzymes. Our analyses underscore the importance of scanning the tree of life for new gene lineages to understand phenotypic diversity and gain detailed insights into their function.

evolutionary biology↗

bioRxiv2019

Presence of a D2 receptor truncated protein in the brain of the D2 receptor functional knockout mouse, revisiting its molecular and neurochemical features

Null mice for the dopamine D2 receptor (D2R) have been instrumental in understanding the function of this protein in the central nervous system. Several lines of D2R knockout mice have been generated, which share some characteristics but differ in others. The D2R functional knockout mouse, first described in 1997, is functionally null for D2R-mediated signaling but the Drd2 gene was interrupted at the most extreme distal end leaving open the question about whether transcript and protein are produced. We decided to determine if there are D2R transcripts, the characteristics of these transcripts and whether they are translated in the brain of D2R functional knockout mice. Sequence analysis of 3 Rapid Amplification of cDNA Ends showed that D2R functional knockout mice express transcripts that lack only the exon eight. Immunofluorescence showed D2R-like protein in the brain of the knockout mice. As previously reported, D2R functional knockout mice are hypoactive and insensitive to the D2R agonist quinpirole (QNP). However, the heterozygous showed locomotor activity and response to QNP similar to the wild-type mice. Intriguingly, microdialysis experiments showed that heterozygous mice, such as knockouts, have half the normal levels of synaptic dopamine in the striatum. However, heterozygous mice responded similarly to wild-type mice to an acute injection of QNP, showing a 50% decrease in synaptic dopamine. In conclusion, D2R functional knockout mice express transcripts that lead to a truncated D2R protein that lacks from the sixth transmembrane domain to the C-terminal end but retains the third intracellular loop. We discuss the implications of this truncated D2R coexisting with the native D2R that may explain the unexpected outcomes observed in the heterozygous. Finally, we suggest that the D2R functional knockout mouse can be a useful model for studying protein-protein interaction and trafficking of D2R.

neuroscience↗