TY - JOUR

T1 - 45S rDNA Repeats of Turtles and Crocodiles Harbor a Functional 5S rRNA Gene Specifically Expressed in Oocytes

AU - Davidian, Asya G.

AU - Dyomin, Alexander G.

AU - Galkina, Svetlana A.

AU - Makarova, Nadezhda E.

AU - Dmitriev, Sergey E.

AU - Gaginskaya, Elena R.

N1 - Asya G Davidian, Alexander G Dyomin, Svetlana A Galkina, Nadezhda E Makarova, Sergey E Dmitriev, Elena R Gaginskaya, 45S rDNA Repeats of Turtles and Crocodiles Harbor a Functional 5S rRNA Gene Specifically Expressed in Oocytes, Molecular Biology and Evolution, Volume 39, Issue 1, January 2022, msab324, https://doi.org/10.1093/molbev/msab324

PY - 2022/1/7

Y1 - 2022/1/7

N2 - In most eukaryotic genomes, tandemly repeated copies of 5S rRNA genes are clustered outside the nucleolus organizer region (NOR), which normally encodes three other major rRNAs: 18S, 5.8S, and 28S. Our analysis of turtle rDNA sequences has revealed a 5S rDNA insertion into the NOR intergenic spacer in antisense orientation. The insertion (hereafter called NOR-5S rRNA gene) has a length of 119 bp and coexists with the canonical 5S rDNA clusters outside the NOR. Despite the ∼20% nucleotide difference between the two 5S gene sequences, their internal control regions for RNA polymerase III are similar. Using the turtle Trachemys scripta as a model species, we showed the NOR-5S rDNA specific expression in oocytes. This expression is concurrent with the NOR rDNA amplification during oocyte growth. We show that in vitellogenic oocytes, the NOR-5S rRNA prevails over the canonical 5S rRNA in the ribosomes, suggesting a role of modified ribosomes in oocyte-specific translation. The orders Testudines and Crocodilia seem to be the only taxa of vertebrates with such a peculiar rDNA organization. We speculate that the amplification of the 5S rRNA genes as a part of the NOR DNA during oogenesis provides a dosage balance between transcription of all the four ribosomal RNAs while producing a maternal pool of extra ribosomes. We further hypothesize that the NOR-5S rDNA insertion appeared in the Archelosauria clade during the Permian period and was lost later in the ancestors of Aves.

AB - In most eukaryotic genomes, tandemly repeated copies of 5S rRNA genes are clustered outside the nucleolus organizer region (NOR), which normally encodes three other major rRNAs: 18S, 5.8S, and 28S. Our analysis of turtle rDNA sequences has revealed a 5S rDNA insertion into the NOR intergenic spacer in antisense orientation. The insertion (hereafter called NOR-5S rRNA gene) has a length of 119 bp and coexists with the canonical 5S rDNA clusters outside the NOR. Despite the ∼20% nucleotide difference between the two 5S gene sequences, their internal control regions for RNA polymerase III are similar. Using the turtle Trachemys scripta as a model species, we showed the NOR-5S rDNA specific expression in oocytes. This expression is concurrent with the NOR rDNA amplification during oocyte growth. We show that in vitellogenic oocytes, the NOR-5S rRNA prevails over the canonical 5S rRNA in the ribosomes, suggesting a role of modified ribosomes in oocyte-specific translation. The orders Testudines and Crocodilia seem to be the only taxa of vertebrates with such a peculiar rDNA organization. We speculate that the amplification of the 5S rRNA genes as a part of the NOR DNA during oogenesis provides a dosage balance between transcription of all the four ribosomal RNAs while producing a maternal pool of extra ribosomes. We further hypothesize that the NOR-5S rDNA insertion appeared in the Archelosauria clade during the Permian period and was lost later in the ancestors of Aves.

KW - 5S rRNA genes

KW - IGS

KW - oocyte

KW - rDNA amplification

KW - specialized ribosomes

KW - Archelosauria

KW - Alligators and Crocodiles/genetics

KW - DNA, Ribosomal/genetics

KW - Oocytes

KW - Animals

KW - RNA, Ribosomal, 5S/genetics

KW - Turtles/genetics

KW - Genes, rRNA

UR - https://www.mendeley.com/catalogue/a3a49f67-82ae-3dad-8451-e78e4e18a776/

UR - http://www.scopus.com/inward/record.url?scp=85123878122&partnerID=8YFLogxK

U2 - 10.1093/molbev/msab324

DO - 10.1093/molbev/msab324

M3 - Article

C2 - 34905062

VL - 39

JO - Molecular Biology and Evolution

JF - Molecular Biology and Evolution

SN - 0737-4038

IS - 1

M1 - msab324

ER -