Conversion of adult pancreatic alpha-cells to beta-cells after extreme beta-cell loss.

Pancreatic insulin-producing beta-cells have a long lifespan, such that in healthy conditions they replicate little during a lifetime. Nevertheless, they show increased self-duplication after increased metabolic demand or after injury (that is, beta-cell loss). It is not known whether adult mammals can differentiate (regenerate) new beta-cells after extreme, total beta-cell loss, as in diabetes.

Experimental models of beta-cell regeneration.

The control of glucose metabolism by pancreatic endocrine cells throughout life relies on a tight regulation of the mass of insulin-producing beta-cells. How this homoeostasis is achieved is not well understood. Over the last few years, experimental rodent models with altered beta-cell mass, and, more recently, new transgenic approaches designed to tackle this problem, have provided abundant information.

Pax-6 and c-Maf functionally interact with the alpha-cell-specific DNA element G1 in vivo to promote glucagon gene expression.

Specific expression of the glucagon gene in the rat pancreas requires the presence of the G1 element localized at -100/-49 base pairs on the promoter. Although it is known that multiple transcription factors such as Pax-6, Cdx-2/3, c-Maf, Maf-B, and Brain-4 can activate the glucagon gene promoter through G1, their relative importance in vivo is unknown. We first studied the expression of Maf-B, c-Maf, and Cdx-2/3 in the developing and adult mouse pancreas.

The zinc finger-containing transcription factor Gata-4 is expressed in the developing endocrine pancreas and activates glucagon gene expression.

Gene inactivation studies have shown that members of the Gata family of transcription factors are critical for endoderm development throughout evolution. We show here that Gata-4 and/or Gata-6 are not only expressed in the adult exocrine pancreas but also in glucagonoma and insulinoma cell lines, whereas Gata-5 is restricted to the exocrine pancreas. During pancreas development, Gata-4 is expressed already at embryonic d 10.

Decreased beta-cell proliferation impairs the adaptation to pregnancy in rats malnourished during perinatal life.

We investigated the cellular mechanisms responsible for the inability of 8-month-old previously malnourished (PM) females to adapt their beta-cell mass during pregnancy. The evolution during pregnancy of beta-cell fraction, size and proliferation was studied. At day 21 of pregnancy beta-cell fraction increased less in PM than in control females, compared with their non-pregnant values.