There was an error published in Development 139, 33-45.On p. 36, Fig. 1 was incorrectly cited several times in place of Fig. 2. The correct paragraph appears below.The authors apologise to readers for this mistake.To determine if endodermal Notch activation and Hes1 expression depends on Dll1 activity, we analyzed NICD expression in wild-type and Dll1 lacZ/lacZ embryos and EGFP expression in crosses of Tg(Hes1-EGFP) 1Hri and Dll1 lacZ/+ mice. NICD expression was reduced in E10.5 Dll1 lacZ/lacZ embryos compared with controls ( Fig. 2A,B), but appeared to recover, approaching wild-type levels at E11.5 (Fig. 2C,D). Hes1-EGFP expression was normal in E8.25 Dll1 lacZ/lacZ embryos (Fig. 2E,I) but had partly disappeared from the dorsal pancreas endoderm at E9.5 (Fig. 2F,J) and was almost lost at E10.5 (Fig. 2G,K). Remarkably, and coinciding with the reappearance of NICD, Hes1-EGFP expression was restored in E11.5 Dll1 lacZ/lacZ embryos (Fig. 2H,L).

We present the generation of a panel of monoclonal antibodies (F55A10, F55A12, F64A6B4, and F65A2) against the homeodomain transcription factor Nkx6.1, one of the essential transcription factors that regulates the multistep differentiation process of precursor cells into endocrine β-cells in the pancreas. Expression of Nkx6.1 can be detected in developing pancreatic epithelium and in adult insulin-producing β-cells, making this transcription factor a unique β-cell marker. For production of monoclonal antibodies, RBF mice were immunized with a GST-Nkx6.1 fusion protein containing a 66-amino acid C-terminal fragment of rat Nkx6.1. Four clones were established as stable hybridoma cell lines and the produced antibodies were of the mouse IgG1/κ subtype. When applied for immunohistochemistry on frozen sections of adult mouse pancreas, monoclonal antibodies stain specifically the β-cells in the endocrine islets of Langerhans with patterns comparable to that of a previously produced polyclonal rabbit serum. Monoclonal antibodies can be divided into two groups that appear to recognize different epitopes, as determined by competition ELISA. The presented antibodies are useful tools for the further characterization of the role and function of Nkx6.1 in pancreatic development, especially for use in double-labeling experiments with existing polyclonal rabbit antibodies. (J Histochem Cytochem 54:567-574, 2006)

Expression of the basic helix-loop-helix factor Hairy and Enhancer of Split-1 (Hes1) is required for normal development of a number of tissues during embryonic development. Depending on context, Hes1 may act as a Notch signalling effector which promotes the undifferentiated and proliferative state of progenitor cells, but increasing evidence also points to Notch independent regulation of Hes1 expression. Here we use high resolution confocal scanning of EGFP in a novel BAC transgenic mouse reporter line, Tg(Hes1-EGFP)1Hri, to analyse Hes1 expression from embryonic day 7.0 (e7.0). Our data recapitulates some previous observations on Hes1 expression and suggests new, hitherto unrecognised expression domains including expression in the definitive endoderm at early somite stages before gut tube closure and thus preceding organogenesis. This mouse line will be a valuable tool for studies addressing the role of Hes1 in a number of different research areas including organ specification, development and regeneration.

Mutations in , a target gene of the Notch signalling pathway, lead to ectopic pancreas by a poorly described mechanism. Here, we use genetic inactivation of combined with lineage tracing and live imaging to reveal an endodermal requirement for Hes1, and show that ectopic pancreas tissue is derived from the dorsal pancreas primordium. RNA-seq analysis of sorted E10.5 and Pdx1-GFP cells suggested that upregulation of endocrine lineage genes in embryos was the major defect and, accordingly, early pancreas morphogenesis was normalized, and the ectopic pancreas phenotype suppressed, in embryos. In mutants, we found a near total depletion of dorsal progenitors, which was replaced by an anterior Gcg extension. Together, our results demonstrate that aberrant morphogenesis is the cause of ectopic pancreas and that a part of the endocrine differentiation program is mechanistically involved in the dysgenesis. Our results suggest that the ratio of endocrine lineage to progenitor cells is important for morphogenesis and that a strong endocrinogenic phenotype without complete progenitor depletion, as seen in mutants, provokes an extreme dysgenesis that causes ectopic pancreas.

The homeodomain transcription factor Nkx6-1 is essential for proper motor neuron development and development of insulin-producing pancreatic beta-cells. Nkx6-1 is closely related to Nkx6-2 and Nkx6-3, and all three are expressed in the developing central nervous system and in the developing foregut. Immunohistochemical detection of protein expression is an important tool for description of the temporal differences in expression patterns. When several gene family members like the Nkx6 factors have overlapping or juxtaposed expression domains, there is an elevated risk of unrecognized cross-reactivity, and it is therefore crucial to determine the specificities of antibodies against such targets. In this study we have determined the epitope consensus sequences of four monoclonal antibodies against Nkx6-1 using SPOT membranes, and we refined the results by combined peptide recognition and blocking assays. We show that two of the monoclonal anti-Nkx6-1 antibodies specifically recognize Nkx6-1 and do not cross-react to Nkx6-2 and Nkx6-3. The other two monoclonal anti-Nkx6-1 antibodies are specific to Nkx6-1 in mice but do not recognize Nkx6-1 in chicken and human.