The mechanisms behind the cell-specific and compartmentalized expression of gut and pancreatic hormones is largely unknown. We hereby report that deletion of the Pax 4 gene virtually eliminates duodenal and jejunal hormone-secreting cells, as well as serotonin and somatostatin cells of the distal stomach, while deletion of the Pax 6 gene eliminates duodenal GIP cells as well as gastrin and somatostatin cells of the distal stomach. Thus, together, these two genes regulate the differentiation of all proximal gastrointestinal endocrine cells and reflect common pathways for pancreatic and gastrointestinal endocrine cell differentiation.

SUMMARYWe studied the distribution of the homeodomain proteins Pdx-1 and Nkx 6.1 in the developing rat pancreas. During early development, nuclear staining for both Pdx-1 and Nkx 6.1 occurred in most epithelial cells of the pancreatic anlage. Subsequently, Nkx 6.1 became more ␤ -cell-restricted, and Pdx-1 also occurred in other islet cell types and in the duodenal epithelium. During early pancreatic development, cells co-storing insulin and glucagon were regularly detected. The vast majority of these did not possess nuclear staining for either Pdx-1 or Nkx 6.1. Subsequently, cells storing insulin only appeared. Such cells displayed strongly Pdx-1-and Nkx 6.1-positive nuclei. Therefore, Nkx 6.1, like Pdx-1, may be an important factor in pancreatic development and in mature insulin cell function.

Hirschsprung disease, or congenital aganglionic megacolon, is a genetic disorder of neural crest development affecting 1:5,000 newborns. Mutations in the RET proto-oncogene, repeatedly identified in the heterozygous state in both long- and short-segment Hirschsprung patients, lead to loss of both transforming and differentiating capacities of the activated RET through a dominant negative effect when expressed in appropriate cellular systems. The approach of single-strand conformational polymorphism analysis established for all the 20 exons of the RET proto-oncogene, and previously used to screen for point mutations in Hirschsprung patients allowed us to identify seven additional mutations among 39 sporadic and familial cases of Hirschsprung disease (detection rate 18%). This relatively low efficiency in detecting mutations of RET in Hirschsprung patients cannot be accounted by the hypothesis of genetic heterogeneity, which is not supported by the results of linkage analysis in the pedigrees analyzed so far. Almost 74% of the point mutations in our series, as well as in other patient series, were identified among long segment patients, who represented only 25% of our patient population. The finding of a C620R substitution in a patient affected with total colonic aganglionosis confirms the involvement of this mutation in the pathogenesis of different phenotypes (i.e., medullary thyroid carcinoma and Hirschsprung). Finally the R313Q mutation identified for the first time in homozygosity in a child born of consanguineous parents is associated with the most severe Hirschsprung phenotype (total colonic aganglionosis with small bowel involvement).

We have evaluated the long-term prognosis in an unselected group of adult patients either uni-nephrectomized in childhood because of hydronephrosis or born with unilateral renal agenesis. Thirty-six patients aged 7-47 years were followed for 7-40 years. In 23 control subjects aged 20-47 years the glomerular filtration rate (GFR) and the p-aminohippuric acid clearance (CPAH) did not change significantly with age. In patients with a single kidney the size of that kidney was larger and GFR and CPAH were higher than single kidney values in control subjects. However, in patients with a single kidney since childhood the GFR and the CPAH declined slowly but significantly during the follow-up period. Significant microalbuminuria occurred in 47% of the patients with a single kidney and was more frequent with a longer follow-up period. No patient had renal insufficiency or a marked increase in arterial blood pressure. We conclude that in patients with a single kidney since childhood the long-term prognosis is good, but the late decrease in GFR and increase in albumin excretion may indicate a moderate risk for premature renal damage.

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The outer 150-micrometers layer of the renal cortex of the rat consists mainly of proximal tubules (PT). In this layer Na-K-ATPase (mumol Pi . mg protein-1 . h-1) increases from 3.45 +/- 0.19 (SE) in 10-day-old rats (R10) to 5.90 +/- 0.28 in 20-day-old rats (R20) to 9.52 +/- 0.42 in 40-day-old rats (R40). Betamethasone in pharmacologic doses increases Na-K-ATPase in R10, R20, and R40 to 11.5 +/- 1.19, 13.4 +/- 0.64, and 13.3 +/- 0.60, respectively. Estrogen in pharmacologic doses increases Na-K-ATPase to 9.1 +/- 0.46 in R20 and decreases Na-K-ATPase to 7.6 +/- 0.39 in R40. Aldosterone in a dose of 10 micrograms/100 g BW increases Na-K-ATPase to 8.7 +/- 0.26 in R20; in a dose of 40 micrograms/100 g BW it increases Na-K-ATPase to 6.9 +/- 0.35 in R10. However, aldosterone in a dose of 80 micrograms/100 g BW is needed to cause an increase in R40 to 13.4 +/- 0.37. Treatment with canrenone from the 10th to the 20th day increases Na-K-ATPase. It is concluded that the immature PT cells are particularly sensitive to hormone induction of Na-K-ATPase and that the sensitivity is maximal during fairly late stages of cellular differentiation. Moreover, the inductive effect is probably mediated via glucocorticoid receptors.

SUMMARYThe homeobox gene product Nkx 6.1 is of unknown function but is expressed in the pancreas and the antropyloric mucosa of the stomach. In the adult pancreas, Nkx 6.1 possesses an insulin cell-restricted distribution, whereas its localization in the stomach is unknown. We now show that the vast majority of serotonin-producing enterochromaffin cells of the antropyloric mucosa contain Nkx 6.1-immunoreactive nuclei. In addition, a subpopulation of cells co-storing serotonin and gastrin display Nkx 6.1-positive nuclei. Such cells have been postulated to represent precursors of mature gastrin and serotonin cells. The nuclei of the co-storing cells have previously also been found to be positive for another homeodomain protein, Pdx-1. Pdx-1-deficient animals were therefore investigated and were found to be devoid of Nkx 6.1-positive nuclei. Our data show that Pdx-1 is needed for Nkx 6.1 expression and suggest a role for Nkx 6.1 in the maturation of gastrin-and serotonin-positive precursor cells.

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