title: Postembryonic Nephrogenesis and Persistence of Six2-Expressing Nephron Progenitor Cells in the Reptilian Kidney.
abstract: New nephron formation (nephrogenesis) ceases in mammals around birth and is completely absent in adults. In contrast, postembryonic nephrogenesis is well documented in the mesonephric kidneys of fishes and amphibians. The transient mesonephros in reptiles (including birds) and mammals is replaced by the metanephros during embryogenesis. Thus, one may speculate that postembryonic nephrogenesis is restricted to the mesonephric kidney. Previous reports have suggested the metanephros of non-avian reptiles (hereafter reptiles) may continually form nephrons throughout life. We investigated the presence of adult nephrogenesis in reptiles by examining adult kidneys from several species including Trachemys scripta, Chrysemys picta, Boa constrictor, Tupinambis tegu, Anolis carolinensis, and Alligator mississipiensis among others. We found that all major reptilian groups (Testudines, Crocodylia, and Squamates) showed the presence of adult nephrogenesis. The total amount of nephrogenesis varied greatly between species with turtles displaying the highest density of nephrogenesis. In contrast, we were unable to detect adult nephrogenesis in monotremes, and in the iguanid A. carolinensis. Nephron progenitor cells express the transcription factor Six2, which in mammals, becomes downregulated as the progenitor cell population is exhausted and nephrogenesis ends. Using the alligator as a model, we were able to detect Six2-positive cap mesenchyme cells in the adult kidney, which spatially correlated with areas of nephrogenesis. These results suggest that the metanephric kidney of reptiles has maintained the ability to continually grow new nephrons during postembryonic life, a process lost early in mammalian evolution, likely due to the persistence of a Six2-expressing progenitor cell population.
authors.affiliation: Department of Biomedical Sciences, NYIT College of Osteopathic Medicine, Old Westbury, New York, United States of America.
authors.forename: Troy
authors.initials: T
authors.lastname: Camarata
authors.affiliation: Department of Biomedical Sciences, NYIT College of Osteopathic Medicine, Old Westbury, New York, United States of America.
authors.forename: Alexis
authors.initials: A
authors.lastname: Howard
authors.affiliation: Louisiana Department of Wildlife and Fisheries, Grand Chenier, Louisiana, United States of America.
authors.forename: Ruth M
authors.initials: RM
authors.lastname: Elsey
authors.affiliation: Department of Biomedical Sciences, NYIT College of Osteopathic Medicine, Old Westbury, New York, United States of America.
authors.forename: Sarah
authors.initials: S
authors.lastname: Raza
authors.affiliation: Department of Biomedical Sciences, NYIT College of Osteopathic Medicine, Old Westbury, New York, United States of America.
authors.forename: Alice
authors.initials: A
authors.lastname: O'Connor
authors.affiliation: Department of Anatomy, NYIT College of Osteopathic Medicine, Old Westbury, New York, United States of America.
authors.forename: Brian
authors.initials: B
authors.lastname: Beatty
authors.affiliation: Department of Anatomy, NYIT College of Osteopathic Medicine, Old Westbury, New York, United States of America.
authors.forename: Jack
authors.initials: J
authors.lastname: Conrad
authors.affiliation: Department of Anatomy, NYIT College of Osteopathic Medicine, Old Westbury, New York, United States of America.
authors.forename: Nikos
authors.initials: N
authors.lastname: Solounias
authors.affiliation: Department of Biomedical Sciences, NYIT College of Osteopathic Medicine, Old Westbury, New York, United States of America.
authors.forename: Priscilla
authors.initials: P
authors.lastname: Chow
authors.affiliation: Department of Biomedical Sciences, NYIT College of Osteopathic Medicine, Old Westbury, New York, United States of America.
authors.forename: Saima
authors.initials: S
authors.lastname: Mukta
authors.affiliation: Department of Biomedical Sciences, NYIT College of Osteopathic Medicine, Old Westbury, New York, United States of America.
authors.forename: Aleksandr
authors.initials: A
authors.lastname: Vasilyev
mesh_terms: D000818:Animals; D009399:Nephrons / Q000254:growth & development*; D012104:Reptiles; D013234:Stem Cells / Q000166:cytology*; D015534:Trans-Activators / Q000378:metabolism*
chemical_list: D015534:Trans-Activators