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.


An intestinal cell type in zebrafish is the nexus for the SARS-CoV-2 receptor and the Renin-Angiotensin-Aldosterone System that contributes to COVID-19 comorbidities.

bioRxiv. 2020 Sep 02;:

Authors: Postlethwait JH, Farnsworth DR, Miller AC

People with underlying conditions, including hypertension, obesity, and diabetes, are especially susceptible to negative outcomes after infection with the coronavirus SARS-CoV-2. These COVID-19 comorbidities are exacerbated by the Renin-Angiotensin-Aldosterone System (RAAS), which normally protects from rapidly dropping blood pressure or dehydration via the peptide Angiotensin II (Ang II) produced by the enzyme Ace. The Ace paralog Ace2 degrades Ang II, thus counteracting its chronic effects. Ace2 is also the SARS-CoV-2 receptor. Ace , the coronavirus, and COVID-19 comorbidities all regulate Ace2 , but we don't yet understand how. To exploit zebrafish ( Danio rerio ) as a disease model to understand mechanisms regulating the RAAS and its relationship to COVID-19 comorbidities, we must first identify zebrafish orthologs and co-orthologs of human RAAS genes, and second, understand where and when these genes are expressed in specific cells in zebrafish development. To achieve these goals, we conducted genomic analyses and investigated single cell transcriptomes. Results showed that most human RAAS genes have an ortholog in zebrafish and some have two or more co-orthologs. Results further identified a specific intestinal cell type in zebrafish larvae as the site of expression for key RAAS components, including Ace, Ace2, the coronavirus co-receptor Slc6a19, and the Angiotensin-related peptide cleaving enzymes Anpep and Enpep. Results also identified specific vascular cell subtypes as expressing Ang II receptors, apelin , and apelin receptor genes. These results identify specific genes and cell types to exploit zebrafish as a disease model for understanding the mechanisms leading to COVID-19 comorbidities.
SUMMARY STATEMENT: Genomic analyses identify zebrafish orthologs of the Renin-Angiotensin-Aldosterone System that contribute to COVID-19 comorbidities and single-cell transcriptomics show that they act in a specialized intestinal cell type.

PMID: 32908984 [PubMed]

Related Articles

Sex chromosome and sex locus characterization in goldfish, Carassius auratus (Linnaeus, 1758).

BMC Genomics. 2020 Aug 11;21(1):552

Authors: Wen M, Feron R, Pan Q, Guguin J, Jouanno E, Herpin A, Klopp C, Cabau C, Zahm M, Parrinello H, Journot L, Burgess SM, Omori Y, Postlethwait JH, Schartl M, Guiguen Y

BACKGROUND: Goldfish is an important model for various areas of research, including neural development and behavior and a species of significant importance in aquaculture, especially as an ornamental species. It has a male heterogametic (XX/XY) sex determination system that relies on both genetic and environmental factors, with high temperatures being able to produce female-to-male sex reversal. Little, however, is currently known on the molecular basis of genetic sex determination in this important cyprinid model. Here we used sequencing approaches to better characterize sex determination and sex-chromosomes in an experimental strain of goldfish.
RESULTS: Our results confirmed that sex determination in goldfish is a mix of environmental and genetic factors and that its sex determination system is male heterogametic (XX/XY). Using reduced representation (RAD-seq) and whole genome (pool-seq) approaches, we characterized sex-linked polymorphisms and developed male specific genetic markers. These male specific markers were used to distinguish sex-reversed XX neomales from XY males and to demonstrate that XX female-to-male sex reversal could even occur at a relatively low rearing temperature (18 °C), for which sex reversal has been previously shown to be close to zero. We also characterized a relatively large non-recombining region (~ 11.7 Mb) on goldfish linkage group 22 (LG22) that contained a high-density of male-biased genetic polymorphisms. This large LG22 region harbors 373 genes, including a single candidate as a potential master sex gene, i.e., the anti-Mullerian hormone gene (amh). However, no sex-linked polymorphisms were detected in the coding DNA sequence of the goldfish amh gene.
CONCLUSIONS: These results show that our goldfish strain has a relatively large sex locus on LG22, which is likely the Y chromosome of this experimental population. The presence of a few XX males even at low temperature also suggests that other environmental factors in addition to temperature could trigger female-to-male sex reversal. Finally, we also developed sex-linked genetic markers, which will be important tools for future research on sex determination in our experimental goldfish population. However, additional work would be needed to explore whether this sex locus is conserved in other populations of goldfish.

PMID: 32781981 [PubMed - in process]