John Postlethwait

Professor, Department of Biology
Member, ION

Ph.D. Case Western Reserve
B.S. Stanford Univeristy


Research Interests: Genetic regulation of animal development including development of the nervous system, the mechanisms of sex determination, the origin of novel morphologies in evolution and the evolution of the vertebrate genome.

Overview: Our laboratory is interested in the genetic, genomic, and evolutionary principles that guide animal development. We investigate several aspects of this main problem: 

Genome Duplication: The evolution of gene functions in development after genome duplication, focusing on skeletal development.

Fanconi anemia: A small molecule screen for compounds to rescue zebrafish Fanconi Anemia mutants as a way to identify potential therapeutics for human FA patients and to understand disease mechanisms.

MicroRNAs: The roles of microRNAs in embryonic (especially skeletal) development, including evolving miRNA functions after genome duplication.

Icefish: The genetic basis for the evolution of osteopenia or osteoporosis in Antarctic icefish.

Sex determinaion:The developmental genetic basis for sex determination in zebrafish.

Speciation: The roles of genome duplication in lineage divergence, focusing on the evolution of cis and trans acting regulation in the radiation of the danio lineage, including zebrafish, and on variation among populations of stickleback.

Oikopleura: Retaining a chordate body plan as an adult, the larvacean urochordate Oikopleura dioica represents the sister lineage to the vertebrates, diverging before the R1 and R2 rounds of genome duplication that led to the origin of vertebrate innovations.

Perchlorate toxicity and sex determination: Perchlorate is a pervasive environmental contaminant that can cause partial sex reversal in stickleback. We are investigating the hypotheses that perchlorate alters sex development through the thyroid or a non-thyroidal mechanism.

Drosophila developmental genetics: Work on Drosophila homeotic mutants, pattern formation, and ovary development.


Mol Biol Evol. 2022 Jan 10:msac004. doi: 10.1093/molbev/msac004. Online ahead of print.


microRNAs are important post-transcriptional regulators of gene expression involved in countless biological processes and are widely studied across metazoans. While miRNA research continues to grow, the large community of fish miRNA researchers lacks exhaustive resources consistent among species. To fill this gap, we developed FishmiRNA, an evolutionarily supported microRNA annotation and expression database for ray-finned fishes: The self-explanatory database contains detailed, manually-curated miRNA annotations with orthology relationships rigorously established by sequence similarity and conserved syntenies, and expression data provided for each detected mature miRNA. In just few clicks, users can download the annotation and expression database in several convenient formats either in its entirety or a subset. Simple filters and BLAST search options also permit the simultaneous exploration and visual comparison of expression data for up to any ten mature miRNAs across species and organs. FishmiRNA was specifically designed for ease of use to reach a wide audience.

PMID:35020925 | DOI:10.1093/molbev/msac004

BMC Biol. 2021 Nov 16;19(1):235. doi: 10.1186/s12915-021-01163-5.


BACKGROUND: Circulating miRNAs (c-miRNAs) are found in most, if not all, biological fluids and are becoming well-established non-invasive biomarkers of many human pathologies. However, their features in non-pathological contexts and whether their expression profiles reflect normal life history events have received little attention, especially in non-mammalian species. The aim of the present study was to investigate the potential of c-miRNAs to serve as biomarkers of reproductive and metabolic states in fish.

RESULTS: The blood plasma was sampled throughout the reproductive cycle of female rainbow trout subjected to two different feeding regimes that triggered contrasting metabolic states. In addition, ovarian fluid was sampled at ovulation, and all samples were subjected to small RNA-seq analysis, leading to the establishment of a comprehensive miRNA repertoire (i.e., miRNAome) and enabling subsequent comparative analyses to a panel of RNA-seq libraries from a wide variety of tissues and organs. We showed that biological fluid miRNAomes are complex and encompass a high proportion of the overall rainbow trout miRNAome. While sharing a high proportion of common miRNAs, the blood plasma and ovarian fluid miRNAomes exhibited strong fluid-specific signatures. We further revealed that the blood plasma miRNAome significantly changed depending on metabolic and reproductive states. We subsequently identified three evolutionarily conserved muscle-specific miRNAs or myomiRs (miR-1-1/2-3p, miR-133a-1/2-3p, and miR-206-3p) that accumulated in the blood plasma in response to high feeding rates, making these myomiRs strong candidate biomarkers of active myogenesis. We also identified miR-202-5p as a candidate biomarker for reproductive success that could be used to predict ovulation and/or egg quality.

CONCLUSIONS: Together, these promising results reveal the high potential of c-miRNAs, including evolutionarily conserved myomiRs, as physiologically relevant biomarker candidates and pave the way for the use of c-miRNAs for non-invasive phenotyping in various fish species.

PMID:34781956 | DOI:10.1186/s12915-021-01163-5

Virology. 2021 Nov 2;565:65-72. doi: 10.1016/j.virol.2021.10.007. Online ahead of print.


Fish papillomaviruses form a newly discovered group broadly recognized as the Secondpapillomavirinae subfamily. This study expands the documented genomes of the fish papillomaviruses from six to 16, including one from the Antarctic emerald notothen, seven from commercial market fishes, one from data mining of sea bream sequence data, and one from a western gull cloacal swab that is likely diet derived. The genomes of secondpapillomaviruses are ∼6 kilobasepairs (kb), which is substantially smaller than the ∼8 kb of terrestrial vertebrate papillomaviruses. Each genome encodes a clear homolog of the four canonical papillomavirus genes, E1, E2, L1, and L2. In addition, we identified open reading frames (ORFs) with short linear peptide motifs reminiscent of E6/E7 oncoproteins. Fish papillomaviruses are extremely diverse and phylogenetically distant from other papillomaviruses suggesting a model in which terrestrial vertebrate-infecting papillomaviruses arose after an evolutionary bottleneck event, possibly during the water-to-land transition.

PMID:34739918 | DOI:10.1016/j.virol.2021.10.007