Connective tissue growth factor (CTGF) inactivation leads to defects in islet cell lineage allocation and beta-cell proliferation during embryogenesis.

The factors necessary for normal pancreatic islet morphogenesis have not been well characterized. Here we report that connective tissue growth factor (CTGF) is involved in the establishment of normal islet endocrine cell ratio and architecture. CTGF is a secreted protein known to modulate several growth factor-signaling pathways including TGF-beta, BMP, and Wnt. Although its role in pancreatic diseases such as pancreatitis and pancreatic cancer are well documented, a role for CTGF in normal pancreas development and function has heretofore not been examined. Using a lacZ-tagged CTGF allele, we describe for the first time the expression pattern of CTGF in the developing pancreas and the requirement of CTGF for normal islet morphogenesis and embryonic beta-cell proliferation. CTGF is highly expressed in pancreatic ductal epithelium and vascular endothelium, as well as at lower levels in developing insulin(+) cells, but becomes down-regulated in beta-cells soon after birth. Pancreata from CTGF null embryos have an increase in glucagon(+) cells with a concomitant decrease in insulin(+) cells, and show defects in islet morphogenesis. Loss of CTGF also results in a dramatic decrease in beta-cell proliferation at late gestation. Unlike CTGF null embryos, CTGF heterozygotes survive past birth and exhibit a range of islet phenotypes, including an intermingling of islet cell types, increased number of glucagon(+) cells, and beta-cell hypertrophy.

Gene expression profiling of a mouse model of pancreatic islet dysmorphogenesis.

BACKGROUND: In the past decade, several transcription factors critical for pancreas organogenesis have been identified. Despite this success, many of the factors necessary for proper islet morphogenesis and function remain uncharacterized. Previous studies have shown that transgenic over-expression of the transcription factor Hnf6 specifically in the pancreatic endocrine cell lineage resulted in disruptions in islet morphogenesis, including dysfunctional endocrine cell sorting, increased individual islet size, increased number of peripheral endocrine cell types, and failure of islets to migrate away from the ductal epithelium. The mechanisms whereby maintained Hnf6 causes defects in islet morphogenesis have yet to be elucidated. METHODOLOGY/PRINCIPAL FINDINGS: We exploited the dysmorphic islets in Hnf6 transgenic animals as a tool to identify factors important for islet morphogenesis. Genome-wide microarray analysis was used to identify differences in the gene expression profiles of late gestation and early postnatal total pancreas tissue from wild type and Hnf6 transgenic animals. Here we report the identification of genes with an altered expression in Hnf6 transgenic animals and highlight factors with potential importance in islet morphogenesis. Importantly, gene products involved in cell adhesion, cell migration, ECM remodeling and proliferation were found to be altered in Hnf6 transgenic pancreata, revealing specific candidates that can now be analyzed directly for their role in these processes during islet development. CONCLUSIONS/SIGNIFICANCE: This study provides a unique dataset that can act as a starting point for other investigators to explore the role of the identified genes in pancreatogenesis, islet morphogenesis and mature beta cell function.

Oxygen-evolving enhancer protein 2 is phosphorylated by glycine-rich protein 3/wall-associated kinase 1 in Arabidopsis.

The Arabidopsis wall-associated receptor kinase, WAK1, is a member of WAK family that links the plasma membrane to the extracellular matrix. A glycine-rich secreted protein, AtGRP-3, was previously shown to regulate WAK1 functions through binding to the extracellular domain of WAK1. In this study, we sought to determine the downstream molecules of the AtGRP-3/WAK1 signaling pathway, by using two-dimensional gel electrophoresis combined with Edman sequencing and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS). We report here that a chloroplast protein, oxygen-evolving enhancer protein 2 (OEE2), specifically interacts with the cytoplasmic kinase domain of WAK1 and becomes phosphorylated in an AtGRP-3-dependent manner. The phosphorylation of OEE2 is also induced in Arabidopsis by treatment with avirulent Pseudomonas syringae. Taken together, these results suggest that OEE2 activity is regulated by AtGRP-3/WAK1.