Biology subjects

Igaki, T.

Publications and source records attributed to Igaki, T..

3 recordsLinked to original sources

bioRxiv2023

Exocytosis coordinates epithelial cell-turnover in Drosophila ribosomal protein mutants

Robust tissue growth is orchestrated by the precise coordination of cell death and cell proliferation. Our previous study found that in the developing wing pouches of Drosophila Minute/+ animals, both cell death and compensatory cell proliferation are dramatically increased, which contributes to robust growth of mutant tissue. The induction of this cell-turnover depends on activation of JNK signaling, although the mechanism by which JNK activation induces cell-turnover remained unclear. Here, we show that JNK-mediated elevation of exocytosis in dying cells is crucial for triggering cell-turnover in M/+ wing morphogenesis. Mechanistically, elevated JNK signaling in dying cells upregulates exocytosis-related genes and Wingless (Wg), leading to enhanced Wg secretion. Furthermore, this exocytosis-mediated Wg secretion generally occurs downstream of JNK signaling, regardless of the genetic background. Overall, our findings provide mechanistic insights into robust tissue growth through the orchestration of cell-turnover, which is primarily governed by JNK-mediated exocytosis during Drosophila Minute/+ wing morphogenesis.

developmental biology↗

bioRxiv2023

Post-fertilization transcription initiation in an ancestral LTR retrotransposon drives lineage-specific genomic imprinting of ZDBF2

The imprinted ZDBF2 gene is controlled by oocyte-derived DNA methylation, but its epigenetic regulation is quite different from that of other canonically imprinted genes that are dependent on DNA methylation deposited in the gametes. At the ZDBF2 locus, maternal DNA methylation in the imprinted differentially methylated region (DMR) does not persist after implantation. Instead, a transient transcript expressed in the early embryo exclusively from the unmethylated paternal allele of the DMR, known as GPR1-AS in humans and Liz in mice, contributes to establishing secondary DMRs that maintain paternal expression of ZDBF2 in the somatic lineage. While the imprinting of ZDBF2 is evident in humans and mice, whether this process is conserved in other mammals has not been addressed. Here, we show that the first exon of human GPR1-AS overlaps with that of a long terminal repeat (LTR) belonging to the MER21C subfamily of retrotransposons. Although this LTR family appears and is amplified in Boroeutherians, the magnorder of placental mammals that includes the Euarchontoglires and Laurasiatheria superorders, the MER21C insertion into the GPR1-AS orthologous region occurred specifically in the common ancestor of Euarchontoglires, a clade that includes extant primates, rodents, and rabbits. The first exon of mouse Liz does not overlap with an annotated LTR in standard repeat annotation; however, promoter activity assay and multiple sequence alignment suggests that it retains a functionally conserved relationship with the MER21C-overlapping first exon of GPR1-AS. Furthermore, directional RNA sequencing of placental tissues from rabbits and nonhuman primates also revealed GPR1-AS orthologs, with their first exon embedded within the same ancestral LTR. In contrast, allele-specific expression profiling of cow and tammar wallaby, mammals outside the Euarchontoglires group, revealed expression from both alleles in all tissues analyzed. Taken together, these observations suggest that imprinting of ZDBF2 in Euarchontoglires had its genesis in the insertion of a MER21C element in their common ancestor. Our previous studies showed that LTRs reactivated in oocytes contribute to lineage-specific imprinting during mammalian evolution. The data presented here suggest that post-fertilization activation of an ancestral LTR-derived sequence can also contribute to the lineage-specific establishment of imprinted genes.

genomics↗

bioRxiv2022

Tumor elimination by clustered microRNAs miR-306 and miR-79 via non-canonical activation of JNK signaling

JNK signaling plays a critical role in both tumor promotion and tumor suppression. Here, we identified clustered microRNAs (miRNAs) miR-306 and miR-79 as novel tumor-suppressor miRNAs that specifically eliminate JNK-activated tumors in Drosophila. While showing no significant effect on normal tissue growth, miR-306 and miR-79 strongly suppressed growth of multiple tumor models including malignant tumors caused by Ras activation and cell polarity defects. Mechanistically, these miRNAs commonly target the mRNA of an E3 ubiquitin ligase Drosophila ring finger protein 146 (dRNF146). We found that DRNF146 promotes degradation of tankyrase (Tnks), an ADP-ribose polymerase that promotes JNK activation in a non-canonical manner. Thus, downregulation of dRNF146 by miR-306 and miR-79 leads to hyper-enhancement of JNK activation. Our data show that, while JNK activity is essential for tumor growth, elevation of miR-306 or miR-79 overactivate JNK signaling to the lethal level via non-canonical JNK pathway and thus eliminate tumors, providing a new miRNA-based strategy against cancer.

cell biology↗