The theoretical underpinnings of photoacoustic ultrasound (PAUS) reconstruction tomography are presented. A formal relationship between PAUS signals and the heterogeneous distribution of optical absorption within the object being investigated is developed. Based on this theory, a reconstruction approach, analogous to that used in x-ray computed tomography, is suggested. Initial experimental results suggest that this approach produces "reasonable" reconstructions for absorbers distributed within a narrow plane embedded within a highly scattering medium.

RAS is one of the most well-known proto-oncogenes. Its gain-of-function mutations occur in approximately 30% of all human cancers. As the most frequently mutated RAS isoform, KRAS is intensively studied in the past years. Despite its well-recognized importance in cancer malignancy, continuous efforts in the past three decades failed to develop approved therapies for KRAS mutant cancer. KRAS has thus long been considered to be undruggable. Encouragingly, recent studies have aroused renewed interest in the development of KRAS inhibitors either directly towards mutant KRAS or against the crucial steps required for KRAS activation. This review summarizes the most recent progress in the exploration of KRAS-targeted anticancer strategies and hopefully provides useful insights for the field.

SUMMARYBone morphogenetic protein (BMP) signaling plays a crucial role in maintaining the pluripotency of mouse embryonic stem cells (ESCs) and has negative effects on ESC neural differentiation. However, it remains unclear when and how BMP signaling executes those different functions during neural commitment. Here, we show that a BMP4-sensitive window exists during ESC neural differentiation. Cells at this specific period correspond to the egg cylinder stage epiblast and can be maintained as ESC-derived epiblast stem cells (ESD-EpiSCs), which have the same characteristics as EpiSCs derived from mouse embryos. We propose that ESC neural differentiation occurs in two stages: first from ESCs to ESD-EpiSCs and then from ESD-EpiSCs to neural precursor cells (NPCs). We further show that BMP4 inhibits the conversion of ESCs into ESD-EpiSCs during the first stage, and suppresses ESDEpiSC neural commitment and promotes non-neural lineage differentiation during the second stage. Mechanistic studies show that BMP4 inhibits FGF/ERK activity at the first stage but not at the second stage; and IDs, as important downstream genes of BMP signaling, partially substitute for BMP4 functions at both stages. We conclude that BMP signaling has distinct functions during different stages of ESC neural commitment.

Despite the high initial response rates to PARP inhibitors (PARPi) in BRCA-mutated epithelial ovarian cancers (EOC), PARPi resistance remains a major challenge. Chemical modifications of RNAs have emerged as a new layer of epigenetic gene regulation. N 6 -methyladenosine (m 6 A) is the most abundant chemical modification of mRNA, yet the role of m 6 A modification in PARPi resistance has not previously been explored. Here, we show that m 6 A modification of FZD10 mRNA contributes to PARPi resistance by upregulating the Wnt/b-catenin pathway in BRCA-mutated EOC cells. Global m 6 A profile revealed a significant increase in m 6 A modification in FZD10 mRNA, which correlated with increased FZD10 mRNA stability and an upregulation of the Wnt/b-catenin pathway. Depletion of FZD10 or inhibition of the Wnt/b-catenin sensitizes resistant cells to PARPi. Mechanistically, downregulation of m 6 A demethylases FTO and ALKBH5 was suffi-cient to increase FZD10 mRNA m 6 A modification and reduce PARPi sensitivity, which correlated with an increase in homologous recombination activity. Moreover, combined inhibition of PARP and Wnt/b-catenin showed synergistic suppression of PARPi-resistant cells in vitro and in vivo in a xenograft EOC mouse model. Overall, our results show that m 6 A contributes to PARPi resistance in BRCA-deficient EOC cells by upregulating the Wnt/b-catenin pathway via stabilization of FZD10. They also suggest that inhibition of the Wnt/b-catenin pathway represents a potential strategy to overcome PARPi resistance.Significance: These findings elucidate a novel regulatory mechanism of PARPi resistance in EOC by showing that m 6 A modification of FZD10 mRNA contributes to PARPi resistance in BRCA-deficient EOC cells via upregulation of Wnt/b-catenin pathway.

Theoretical predictions and experimental measurements of photoacoustic pulse production within a 0.5% solution of Liposyn, a highly scattering, optical propagation medium, are reported. A simple model for photoacoustic energetics is developed that predicts photoacoustic signal pressure as a function of depth within a turbid medium following surface irradiation from an infrared source. The model is valid for very short irradiation duration. The model predicts that the acoustic pressure produced at a distance r from the center of a small, highly absorbing sphere of radius R consists of two, opposite polarity pulses, one originating from the near and one from the far side of the sphere. The magnitude of these biphasic pulses is expected to be proportional to the energy fluence (E) incident on the surface of the sphere and to the ratio, R/r. Furthermore, the energy fluence (E) that reaches the sphere is roughly proportional to e-mu effZ, where mu eff is the effective attenuation coefficient of the turbid medium and Z is the depth of the embedded sphere below the irradiated surface. The variation of E with depth within the absorber and biphasic acoustic pulse production have been verified experimentally. Further experiments demonstrate that a small (3-mm diameter), highly absorbing sphere can be detected and localized at a depth of 37.5 mm within a 0.5% solution of Liposyn with a spatial resolution of 1 x 6 mm2, using a biologically safe level of infrared irradiation (lambda = 1064 nm) and a conventional ultrasound transducer (frequency = 2.25 MHz). These results suggest that photoacoustic ultrasound imaging may have application to biologic systems such as the human breast.

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Methyltransferase-like 3 (METTL3) and 14 (METTL14) are core subunits of the methyltransferase complex (MTC) that catalyzes mRNA N 6 -methyladenosine (m 6 A) modification. Despite the expanding list of m 6 A-dependent function of the MTC, m 6 A independent function of the METTL3 and METTL14 complex remains poorly understood. Here we show that genome-wide redistribution of METTL3 and METTL14 transcriptionally drives senescence-associated secretory phenotype (SASP) in a m 6 A-independent manner. METTL14 is redistributed to the enhancers, while METTL3 is localized to the pre-existing NF-κB sites within the promoters of SASP genes during senescence. METTL3 and METTL14 are necessary for SASP. However, SASP is not regulated by m 6 A mRNA modification. METTL3 and METTL14 are required for both the tumor-promoting and immune surveillance functions of senescent cells mediated by SASP in vivo in mouse models. In summary, our results report a m 6 A independent function of the METTL3 and METTL14 complex in transcriptionally promoting SASP during senescence.

The ectoderm has the capability to generate epidermis and neuroectoderm and plays imperative roles during the early embryonic development. Our recent study uncovered a region with ectodermal progenitor potential in mouse embryo at embryonic day 7.0 and revealed that Nodal inhibition is essential for its formation. Here, we demonstrate that through brief inhibition of Nodal signaling in vitro, mouse embryonic stem cell (ESC)-derived epiblast stem cells (ESD-EpiSCs) could be committed to transient ectodermal progenitor populations, which possess the ability to give rise to neural or epidermal ectoderm in the absence or presence of BMP4, respectively. Mechanistic studies reveal that BMP4 recruits distinct transcriptional targets in ESD-EpiSCs and ectoderm-like cells. Furthermore, FGF-Erk signaling may also be alleviated during the generation of ectoderm-like cells. Thus, our data suggest that instructive interactions among several extracellular signals participate in the commitment of ectoderm from ESD-EpiSCs, which shed new light on the understanding of the formation of ectoderm during the gastrulation in early mouse embryo development.