Hybrid approach reveals details about genes involved in Meyer-Gorlin syndrome

Meier-Gorlin Syndrome (MGS) is a rare hereditary developmental disorder that causes dwarfism, small ears, small brains, patella defects, and other skeletal abnormalities. In severe cases, MGS causes miscarriage and stillbirth.

Igor Chesnokov, Ph.D. And his colleagues at the University of Alabama at Birmingham are studying this recessive autosomal chromosomal abnormality in an unusual way by inserting a mutated human gene into fruit flies. Specifically, they are focusing on one of the genes involved in MGS called Orc6.

In a study published in GeneticsFeatured in the highlights article, they used this animal model to investigate the function of one human Orc6 mutation (lysine 23 to glutamate (K23E)) first reported in 2017. In people with MGS, the K23E mutation Chesnokov team causes an observable developmental disorder similar to the Orc6 mutation previously studied, the substitution of tyrosine 225 with serine (Y225S).

These two mutations are interesting in contrast because position 23 is near the long chain of linked amino acids that fold to form the Orc6 protein, the N-terminal domain. Position 225 is near the end of the Orc6 protein chain or the C-terminal domain.

Orc6 is part of the Origin Recognition Complex (ORC). This protein complex is essential for initiating intracellular DNA replication in yeast, fruit flies, humans, and other eukaryotes. Without DNA division, cells cannot divide and organisms cannot grow. Inadequate division impedes growth, as seen in MGS.

In a previous study of the Y225S mutation published in the American Journal of Medical Genetics, UAB researchers found that the C-terminal domain of Orc6 is important for protein-protein interactions that help build the ORC complex.

In a current study, Chesnokov et al. Found that a K23E mutation in the N-terminal domain of Orc6 disrupts the protein’s ability to bind DNA. This specific binding is an important step in ORC function.

Therefore, the two mutations have different underlying molecular mechanisms, but both cause a loss of pre-replication complex formation and a decrease in DNA replication, producing a similar phenotype in MGS patients.

One of the keys to this study was to create the chimeric Orc6 gene, partly a human gene and partly a fruit fly gene. That’s why I needed it. Incorporating the human Orc6 gene into fruit flies cannot prevent the lethal effects of Orc6 deletion in fruit flies. In other words, the intact human Orc6 cannot replace the function of the fruit fly Orc6 due to the difference in the interaction of Orc6 with the core ORCs of the two organisms.

However, when UAB researchers created a fruit fly hybrid Orc6 in the N-terminal domain in humans and in the C-terminal domain, the hybrid was able to completely save the fruit fly, and the fruit fly grew into an adult indistinguishable from fruit. Fly with wild-type Orc6. This hybrid Orc6 can then be used to test the K23E mutation in fruit flies and study its molecular mechanism.

This hybrid approach has enabled the study of human protein function in animal systems, demonstrating the importance of the evolutionarily conserved variable domain of the Orc6 protein. We believe that this hybrid approach not only opens a broad path for studying new Orc6 mutations for medical and general science purposes, but may also be useful in other humanization models. “

Dr. Igor Chesnokov, University of Alabama at Birmingham

In summary, Chesnokov, a professor of UAB Biochemistry and Molecular Genetics, tested this humanized fly model discriminatoryly on flies, humans, and chimeric Orc6 proteins to show the conserved diverse characteristics of the proteins. It has the unique advantage of being able to reveal. Its function in metazoan cells.

A co-author of the study with Chesnokov, “A humanized Drosophila model of Meyer-Gorlin syndrome reveals a variety of conserved features of the Orc6 protein,” said Maxim Barasov and Catalina Acmetova of the Faculty of UAB Biochemistry and Molecular Genetics. is.

There was support from the National Institute of Medical Sciences grant GM121449.

In related news, UAB received a $ 9.3 million grant from the National Institutes of Health’s Research Infrastructure Program Office this fall to set up a new Precision Animal Modeling Center (C-PAM).

The work of the Chesnokov team is an example of precise disease modeling, including the creation of patient-specific disease models. Often, yeast, worms, fruit flies, zebrafish, frogs, mice, or rats are used. Chesnokov states that adding Drosophila to the C-PAM disease modeling unit can integrate the UAB Fly Lab and provide the UAB community with the expertise they need.

Precision animal models mimic the molecular properties of the condition present in the patient. For example, if a patient suffers from a disease caused by a sequence mutation that leads to genetic dysfunction, C-PAM creates an animal model with this same mutation. By studying the effects of variants on models, it is possible to perform science that is not possible in human patients.