Lin28 paralogs regulate lung branching morphogenesis.

The molecular mechanisms that govern the choreographed timing of organ development remain poorly understood. Our investigation of the role of the Lin28a and Lin28b paralogs during the developmental process of branching morphogenesis establishes that dysregulation of Lin28a/b leads to abnormal branching morphogenesis in the lung and other tissues. Additionally, we find that the Lin28 paralogs, which regulate post-transcriptional processing of both mRNAs and microRNAs (miRNAs), predominantly control mRNAs during the initial phases of lung organogenesis. Target mRNAs include Sox2, Sox9, and Etv5, which coordinate lung development and differentiation. Moreover, we find that functional interactions between Lin28a and Sox9 are capable of bypassing branching defects in Lin28a/b mutant lungs. Here, we identify Lin28a and Lin28b as regulators of early embryonic lung development, highlighting the importance of the timing of post-transcriptional regulation of both miRNAs and mRNAs at distinct stages of organogenesis.

Author Correction: Lin28 and let-7 regulate the timing of cessation of murine nephrogenesis.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The developmental stage of the hematopoietic niche regulates lineage in MLL-rearranged leukemia.

Leukemia phenotypes vary with age of onset. Delineating mechanisms of age specificity in leukemia could improve disease models and uncover new therapeutic approaches. Here, we used heterochronic transplantation of leukemia driven by MLL/KMT2A translocations to investigate the contribution of the age of the hematopoietic microenvironment to age-specific leukemia phenotypes. When driven by MLL-AF9, leukemia cells in the adult microenvironment sustained a myeloid phenotype, whereas the neonatal microenvironment supported genesis of mixed early B cell/myeloid leukemia. In MLL-ENL leukemia, the neonatal microenvironment potentiated B-lymphoid differentiation compared with the adult. Ccl5 elaborated from adult marrow stroma inhibited B-lymphoid differentiation of leukemia cells, illuminating a mechanism of age-specific lineage commitment. Our study illustrates the contribution of the developmental stage of the hematopoietic microenvironment in defining the age specificity of leukemia.

The Lin28/let-7 Pathway Regulates the Mammalian Caudal Body Axis Elongation Program.

The heterochronic genes Lin28a/b and let-7 regulate invertebrate development, but their functions in patterning the mammalian body plan remain unexplored. Here, we describe how Lin28/let-7 influence caudal vertebrae number during body axis formation. We found that FoxD1-driven overexpression of Lin28a strikingly increased caudal vertebrae number and tail bud cell proliferation, whereas its knockout did the opposite. Lin28a overexpression downregulated the neural marker Sox2, causing a pro-mesodermal phenotype with a decreased proportion of neural tissue relative to nascent mesoderm. Manipulating Lin28a and let-7 led to opposite effects, and manipulating Lin28a's paralog, LIN28B caused similar yet distinct phenotypes. These findings suggest that Lin28/let-7 play a role in the regulation of tail length through heterochrony of the body plan. We propose that the Lin28/let-7 pathway controls the pool of caudal progenitors during tail development, promoting their self-renewal and balancing neural versus mesodermal cell fate decisions.

Lin28 and let-7 regulate the timing of cessation of murine nephrogenesis.

In humans and in mice the formation of nephrons during embryonic development reaches completion near the end of gestation, after which no new nephrons are formed. The final nephron complement can vary 10-fold, with reduced nephron number predisposing individuals to hypertension, renal, and cardiovascular diseases in later life. While the heterochronic genes lin28 and let-7 are well-established regulators of developmental timing in invertebrates, their role in mammalian organogenesis is not fully understood. Here we report that the Lin28b/let-7 axis controls the duration of kidney development in mice. Suppression of let-7 miRNAs, directly or via the transient overexpression of LIN28B, can prolong nephrogenesis and enhance kidney function potentially via upregulation of the Igf2/H19 locus. In contrast, kidney-specific loss of Lin28b impairs renal development. Our study reveals mechanisms regulating persistence of nephrogenic mesenchyme and provides a rationale for therapies aimed at increasing nephron mass.

LIN28 cooperates with WNT signaling to drive invasive intestinal and colorectal adenocarcinoma in mice and humans.

Colorectal cancer (CRC) remains a major contributor to cancer-related mortality. LIN28A and LIN28B are highly related RNA-binding protein paralogs that regulate biogenesis of let-7 microRNAs and influence development, metabolism, tissue regeneration, and oncogenesis. Here we demonstrate that overexpression of either LIN28 paralog cooperates with the Wnt pathway to promote invasive intestinal adenocarcinoma in murine models. When LIN28 alone is induced genetically, half of the resulting tumors harbor Ctnnb1 (ß-catenin) mutation. When overexpressed in Apc(Min/+) mice, LIN28 accelerates tumor formation and enhances proliferation and invasiveness. In conditional genetic models, enforced expression of a LIN28-resistant form of the let-7 microRNA reduces LIN28-induced tumor burden, while silencing of LIN28 expression reduces tumor volume and increases tumor differentiation, indicating that LIN28 contributes to tumor maintenance. We detected aberrant expression of LIN28A and/or LIN28B in 38% of a large series of human CRC samples (n = 595), where LIN28 expression levels were associated with invasive tumor growth. Our late-stage CRC murine models and analysis of primary human tumors demonstrate prominent roles for both LIN28 paralogs in promoting CRC growth and progression and implicate the LIN28/let-7 pathway as a therapeutic target.

Lin28 sustains early renal progenitors and induces Wilms tumor.

Wilms Tumor, the most common pediatric kidney cancer, evolves from the failure of terminal differentiation of the embryonic kidney. Here we show that overexpression of the heterochronic regulator Lin28 during kidney development in mice markedly expands nephrogenic progenitors by blocking their final wave of differentiation, ultimately resulting in a pathology highly reminiscent of Wilms tumor. Using lineage-specific promoters to target Lin28 to specific cell types, we observed Wilms tumor only when Lin28 is aberrantly expressed in multiple derivatives of the intermediate mesoderm, implicating the cell of origin as a multipotential renal progenitor. We show that withdrawal of Lin28 expression reverts tumorigenesis and markedly expands the numbers of glomerulus-like structures and that tumor formation is suppressed by enforced expression of Let-7 microRNA. Finally, we demonstrate overexpression of the LIN28B paralog in a significant percentage of human Wilms tumor. Our data thus implicate the Lin28/Let-7 pathway in kidney development and tumorigenesis.

Aberrant islet unfolded protein response in type 2 diabetes.

The endoplasmic reticulum adapts to fluctuations in demand and copes with stress through an adaptive signaling cascade called the unfolded protein response (UPR). Accumulating evidence indicates that the canonical UPR is critical to the survival and function of insulin-producing pancreatic ß-cells, and alterations in the UPR may contribute to the pathogenesis of type 2 diabetes. However, the dynamic regulation of UPR molecules in the islets of animal models and humans with type 2 diabetes remains to be elucidated. Here, we analyzed the expression of activating factor 6 (ATF6α) and spliced X-box binding protein 1 (sXBP1), and phosphorylation of eukaryotic initiation factor 2 (eIF2α), to evaluate the three distinct branches of the UPR in the pancreatic islets of mice with diet- or genetic-induced obesity and insulin resistance. ATF6 and sXBP1 expression was predominantly found in the ß-cells, where hyperglycemia coincided with a decline in expression in both experimental models and in humans with type 2 diabetes. These data suggest alterations in the expression of UPR mediators may contribute to the decline in islet function in type 2 diabetes in mice and humans.

Restoration of the unfolded protein response in pancreatic ß cells protects mice against type 1 diabetes.

Perturbations in endoplasmic reticulum (ER) homeostasis can evoke stress responses leading to aberrant glucose and lipid metabolism. ER dysfunction is linked to inflammatory disorders, but its role in the pathogenesis of autoimmune type 1 diabetes (T1D) remains unknown. We identified defects in the expression of unfolded protein response (UPR) mediators ATF6 (activating transcription factor 6) and XBP1 (X-box binding protein 1) in ß cells from two different T1D mouse models and then demonstrated similar defects in pancreatic ß cells from T1D patients. Administration of a chemical ER stress mitigator, tauroursodeoxycholic acid (TUDCA), at the prediabetic stage resulted in a marked reduction of diabetes incidence in the T1D mouse models. This reduction was accompanied by (i) a significant decrease in aggressive lymphocytic infiltration in the pancreas, (ii) improved survival and morphology of ß cells, (iii) reduced ß cell apoptosis, (iv) preserved insulin secretion, and (v) restored expression of UPR mediators. TUDCA's actions were dependent on ATF6 and were lost in mice with ß cell-specific deletion of ATF6. These data indicate that proper maintenance of the UPR is essential for the preservation of ß cells and that defects in this process can be chemically restored for preventive or therapeutic interventions in T1D.