Tissue regenerative potential displays striking divergence across phylogeny and ontogeny, but the underlying mechanisms remain enigmatic. Loss of mammalian cardiac regenerative potential correlates with cardiomyocyte cell-cycle arrest and polyploidization, as well as the development of postnatal endothermy. We reveal that diploid cardiomyocyte abundance across 41 species conforms to Kleiber’s law−the ¾-power law scaling of metabolism with bodyweight−and inversely correlates with standard metabolic rate, body temperature, and serum thyroxine level. Inactivation of thyroid hormone signaling reduces mouse cardiomyocyte polyploidization, delays cell-cycle exit, and retains cardiac regenerative potential in adults. Conversely, exogenous thyroid hormones inhibit zebrafish heart regeneration. Thus, our findings suggest that loss of heart regenerative capacity in adult mammals is triggered by increasing thyroid hormones and may be a tradeoff for the acquisition of endothermy.

The piRNA machinery is known for its role in mediating epigenetic silencing of transposons. Recent studies suggest that this function also involves piRNA-guided cleavage of transposon-derived transcripts. As many piRNAs also appear to have the capacity to target diverse mRNAs, this raises the intriguing possibility that piRNAs may act extensively as siRNAs to degrade specific mRNAs. To directly test this hypothesis, we compared mouse PIWI (MIWI)-associated piRNAs with experimentally identified cleaved mRNA fragments from mouse testes, and observed cleavage sites that predominantly occur at position 10 from the 5′ end of putative targeting piRNAs. We also noted strong biases for U and A residues at nucleotide positions 1 and 10, respectively, in both piRNAs and mRNA fragments, features that resemble the pattern of piRNA amplification by the 'ping-pong' cycle. Through mapping of MIWI-RNA interactions by CLIP-seq and gene expression profiling, we found that many potential piRNA-targeted mRNAs directly interact with MIWI and show elevated expression levels in the testes of Miwi catalytic mutant mice. Reporter-based assays further revealed the importance of base pairing between piRNAs and mRNA targets and the requirement for both the slicer activity and piRNA-loading ability of MIWI in piRNA-mediated target repression. Importantly, we demonstrated that proper turnover of certain key piRNA targets is essential for sperm formation. Together, these findings reveal the siRNA-like function of the piRNA machinery in mouse testes and its central requirement for male germ cell development and maturation.

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Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) is suggested to be a long (∼7 kb) non-coding RNA. MALAT1 is overexpressed in many human carcinomas, but its function remains unknown. To investigate the role of MALAT1 in human cervical cancer progression, we designed and used short hairpin RNA to inhibit MALAT1 expression in CaSki cells and validated its effect on cell proliferation and invasion. Changes in gene expression were analyzed by reverse transcriptasepolymerase chain reaction. Our data demonstrated that MALAT1 was involved in cervical cancer cell growth, cell cycle progression, and invasion through the regulation of gene expression, such as caspase-3, -8, Bax, Bcl-2, and BclxL, suggesting that MALAT1 could have important implications in cervical cancer biology. Our findings illustrate the biological significance of MALAT1 in cervical cancer progression and provide novel evidence that MALAT1 may serve as a therapeutic target in the prevention of human cervical cancer.

The identity and degree of heterogeneity of glial progenitors and their contributions to brain tumor malignancy remain elusive. By applying lineage-targeted single-cell transcriptomics, we uncover an unanticipated diversity of glial progenitor pools with unique molecular identities in developing brain. Our analysis identifies distinct transitional intermediate states and their divergent developmental trajectories in astroglial and oligodendroglial lineages. Moreover, intersectional analysis uncovers analogous intermediate progenitors during brain tumorigenesis, wherein oligodendrocyte-progenitor intermediates are abundant, hyper-proliferative, and progressively reprogrammed toward a stemlike state susceptible to further malignant transformation. Similar actively cycling intermediate progenitors are prominent components in human gliomas with distinct driver mutations. We further unveil lineage-driving networks underlying glial fate specification and identify Zfp36l1 as necessary for oligodendrocyte-astrocyte lineage transition and glioma growth. Together, our results resolve the dynamic repertoire of common and divergent glial progenitors during development and tumorigenesis and highlight Zfp36l1 as a molecular nexus for balancing glial cell-fate decision and controlling gliomagenesis. (A) Immunolabeling for GFAP and GS in the cortex of P5 hGFAP-GFP mice. (B) The percentage of indicated cells among hGFAP-GFP+ cells in P5 mouse cortices (n = 4 for GFAP; n = 3 for GS and PDGFRa). (C) Immunolabeling for GFAP, Olig2, and Slc1a3 from P5 hGFAP-GFP mice. (D) Zoom on boxed area in (C). (E) The percentage of Olig2+ and Olig2À cells among hGFAP-GFP+GFAP+ (left) or hGFAP-GFP+Slc1a3+ (right) cells in P5 mouse cortices (n = 3). (F) Immunolabeling of Blbp in the cortices from hGFAP-GFP mice at P3. (G) Expression of PDGFRa in the cortices of P5 hGFAP-GFP mice. (H) Immunolabeling for Ppp1r14b and Olig2 in the cortices of hGFAP-GFP mice at P3. (I) Immunolabeling for Olig2 and Ki67 from P5 hGFAP-GFP mice. (J) (Left) Enlarged images of (I) show cells co-labeled with Ki67 (arrows) and cells without Ki67 (arrowheads). (Right) Percentage of Olig2+ and Olig2À cells among Ki67+ hGFAP-GFP+ double-positive cells is shown (>300 cell counts from 3 cortices).

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