Biology subjects

Cortez, D.

Publications and source records attributed to Cortez, D..

3 recordsLinked to original sources

bioRxiv2022

Abasic site ring opening and DNA-protein crosslink reversal by the SRAP protein YedK

Apuirinic/apyrimidinic (AP, or abasic) sites in DNA are one of the most common forms of DNA damage. AP sites are reactive and form crosslinks to both proteins and DNA, are prone to strand breakage, and inhibit DNA replication and transcription. The protein HMCES protects cells from strand breaks, inhibits mutagenic translesion synthesis, and participates in repair of interstrand DNA crosslinks derived from AP sites by forming a stable thiazolidine DNA-protein crosslink (DPC) to AP sites in single-stranded DNA (ssDNA). Despite the importance of HMCES to genome maintenance and the evolutionary conservation of its catalytic SRAP (SOS Response Associated Peptidase) domain, the enzymatic mechanisms of DPC formation and resolution are unknown. Using the bacterial homolog YedK, we show that the SRAP domain catalyzes conversion of the AP site to its reactive, ring-opened aldehyde form, and provide structural evidence for the Schiff base intermediate that forms prior to the more stable thiazolidine. We also report two new activities, whereby SRAP reacts with polyunsaturated aldehydes at DNA 3-ends generated by bifunctional DNA glycosylases and catalyzes direct reversal of the DPC to regenerate the AP site, which provide insight into possible mechanisms by which HMCES DPCs are resolved in cells.

biochemistry↗

bioRxiv2022

A study of thermally-induced sex reversal in casque-headed lizards

Non-avian reptiles, unlike mammals and birds, have undergone numerous sex determination turnovers. For example, casque-headed lizards replaced the ancestral XY system shared across pleurodonts with a new pair of XY chromosomes. However, the evolutionary forces that triggered this transition have remained unclear. An interesting evolutionary hypothesis suggests that species with intermediate states, with sex chromosomes but also thermal-induced sex reversal at specific incubation temperatures, could be more susceptible to sex determination turnovers. We contrasted genotypic data (presence/absence of the Y chromosome) against the histology of gonads of embryos from stages 35-37 incubated at various temperatures, including typical male-producing (26{degrees}C) and female-producing (32{degrees}C) temperatures. We observed perfect concordance between genotype and phenotype at all temperatures. However, analysis of transcriptomic data from embryos incubated at 26{degrees}C and 32{degrees}C identified transcript variants of the chromatin modifiers JARID2 and KDM6B that have been linked to temperature-dependent sex determination in other reptiles. Besides, our work reports for the first time to our knowledge the histology of gonads, including morphological changes, from stages 35-37 of development in the Corytophanidae family. We also observed that all embryos developed hemipenes, suggesting sex-linked developmental heterochrony.Our work tested the validity of a mixed sex determination system in the Corytophanidae family. We showed that XY chromosomes are dominant, however, our work supports the hypothesis of a conserved transcriptional response to incubation temperatures across non-avian reptiles that could be the reminiscence of an ancestral sex determination system.

developmental biology↗

bioRxiv2021

Topoisomerase II poisons inhibit vertebrate DNA replication through distinct mechanisms

Topoisomerase II (Top2) unlinks chromosomes during vertebrate DNA replication. Top2 poisons are widely-used chemotherapeutics that stabilize Top2 complexes on DNA, leading to cytotoxic DNA breaks. However, it is unclear how these drugs affect DNA replication, which is a major target of Top2 poisons. Using Xenopus egg extracts, we show that the Top2 poisons etoposide and doxorubicin both inhibit DNA replication through different mechanisms. Etoposide induces Top2-dependent DNA breaks and induces Top2-dependent fork stalling by trapping Top2 behind replication forks. In contrast, doxorubicin does not lead to appreciable break formation and instead intercalates into parental DNA to inhibit replication fork progression. In human cells, etoposide stalls replication forks in a Top2-dependent manner, while doxorubicin stalls forks independently of Top2. However, both drugs exhibit Top2-dependent cytotoxicity. Thus, despite shared genetic requirements for cytotoxicity etoposide and doxorubicin inhibit DNA replication through distinct mechanisms.

biochemistry↗