The murine neonatal heart can regenerate after injury through cardiomyocyte (CM) proliferation, although this capacity markedly diminishes after the first week of life. Neuregulin-1 (NRG1) administration has been proposed as a strategy to promote cardiac regeneration. Here, using loss- and gain-of-function genetic tools, we explore the role of the NRG1 co-receptor ERBB2 in cardiac regeneration. NRG1-induced CM proliferation diminished one week after birth owing to a reduction in ERBB2 expression. CM-specific Erbb2 knockout revealed that ERBB2 is required for CM proliferation at embryonic/neonatal stages. Induction of a constitutively active ERBB2 (caERBB2) in neonatal, juvenile and adult CMs resulted in cardiomegaly, characterized by extensive CM hypertrophy, dedifferentiation and proliferation, differentially mediated by ERK, AKT and GSK3β/β-catenin signalling pathways. Transient induction of caERBB2 following myocardial infarction triggered CM dedifferentiation and proliferation followed by redifferentiation and regeneration. Thus, ERBB2 is both necessary for CM proliferation and sufficient to reactivate postnatal CM proliferative and regenerative potentials.

BackgroundCompartment boundaries are an essential developmental mechanism throughout evolution, designated to act as organizing centers and to regulate and localize differently fated cells. The hindbrain serves as a fascinating example for this phenomenon as its early development is devoted to the formation of repetitive rhombomeres and their well-defined boundaries in all vertebrates. Yet, the actual role of hindbrain boundaries remains unresolved, especially in amniotes.ResultsHere, we report that hindbrain boundaries in the chick embryo consist of a subset of cells expressing the key neural stem cell (NSC) gene Sox2. These cells co-express other neural progenitor markers such as Transitin (the avian Nestin), GFAP, Pax6 and chondroitin sulfate proteoglycan. The majority of the Sox2+ cells that reside within the boundary core are slow-dividing, whereas nearer to and within rhombomeres Sox2+ cells are largely proliferating. In vivo analyses and cell tracing experiments revealed the contribution of boundary Sox2+ cells to neurons in a ventricular-to-mantle manner within the boundaries, as well as their lateral contribution to proliferating Sox2+ cells in rhombomeres. The generation of boundary-derived neurospheres from hindbrain cultures confirmed the typical NSC behavior of boundary cells as a multipotent and self-renewing Sox2+ cell population. Inhibition of Sox2 in boundaries led to enhanced and aberrant neural differentiation together with inhibition in cell-proliferation, whereas Sox2 mis-expression attenuated neurogenesis, confirming its significant function in hindbrain neuronal organization.ConclusionsData obtained in this study deciphers a novel role of hindbrain boundaries as repetitive pools of neural stem/progenitor cells, which provide proliferating progenitors and differentiating neurons in a Sox2-dependent regulation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12915-016-0277-y) contains supplementary material, which is available to authorized users.

A network of molecular interactions is required in the developing vertebrate hindbrain for the formation and anterior-posterior patterning of the rhombomeres. FGF signaling is required in this network to upregulate the expression of the Krox20 and Kreisler segmentation genes, but little is known of how FGF gene expression is regulated in the hindbrain. We show that the dynamic expression of FGF3 in chick hindbrain segments and boundaries is similar to that of the BMP antagonist, follistatin. Consistent with a regulatory relationship between BMP signaling and FGF3 expression, we find that an increase in BMP activity due to blocking of follistatin translation by morpholino antisense oligonucleotides or overexpression of BMP results in strong inhibition of FGF3 expression. Conversely, addition of follistatin leads to an increase in the level of FGF3 expression. Furthermore, the segmental inhibition of BMP activity by follistatin is required for the expression of Krox20, Hoxb1 and EphA4 in the hindbrain. In addition, we show that the maintenance of FGF3 gene expression requires FGF activity, suggestive of an autoregulatory loop. These results reveal an antagonistic relationship between BMP activity and FGF3 expression that is required for correct segmental gene expression in the chick hindbrain, in which follistatin enables FGF3 expression by inhibiting BMP activity.

The purpose of this study was to assess the clinical relevance, limitations and most common findings of axillary ultrasound and subsequent image-guided aspiration cytology in clinically node-negative breast cancer patients who are at high risk for axillary metastasis. Following institutional review board approval and Health Insurance Portability and Accountability Act (HIPAA) compliance, sonographic axillary surveys from 112 patients considered at high risk for axillary metastases were reviewed retrospectively for the following abnormal features: asymmetric cortical thickening/lobulations; loss or compression of the hyperechoic medullary region; absence of fatty hilum; abnormal lymph node shape; hypoechoic cortex; admixture of normal and abnormal appearing nodes; and increased peripheral blood flow. Patients with either normal or abnormal ultrasound exams, but negative cytology, underwent sentinel node mapping. Patients with abnormal ultrasound and positive cytology proceeded to complete axillary dissection. The number of positive nodes, the size of tumour deposits and the histological pattern of metastatic disease on the positive nodes were then correlated and compared with their corresponding sonographic abnormalities. Abnormalities related to the lymph node cortex were indicative of N1a disease. Features such as loss or compression of the hyperechoic medullary region, absence of fatty hilum, abnormal lymph node shape and increased peripheral blood flow were predictors of N2-3 disease. In conclusion, nodal sonographic characteristics of patients at high risk for metastases are useful predictors of tumour burden in the axilla. When combined with the results from aspiration cytology, these findings could modify the surgical approach to the axilla, eliminating the need for sentinel node mapping in a significant proportion of patients.