Mouse Placental Lactogen-I: RIA and Gestational Profile in Maternal Serum*

Abstract

A RIA for mouse placental lactogen-I (mPL-I) was developed using recombinant mPL-I as the standard, radioligand, and antigen for antiserum production. Displacement curves for dilutions of serum and placental extracts from pregnant mice were parallel to the recombinant mPL-I standard curve. Serum from male and nonpregnant female mice and high concentrations of mouse PRL, GH, PL-II, proliferin, and proliferin-related protein did not cross-react in the assay. mPL-I appeared in maternal serum on day 6 of pregnancy. Its concentration remained low until day 8 and them increased to a very large peak on days 9-11 (maximum concentration, approximately 8 micrograms/ml). The mPL-I concentration declined after day 11, but the hormone could be detected at low concentration in maternal serum until the end of pregnancy. On day 10 of pregnancy, the mPL-I concentration of maternal serum was correlated with litter size. Fractionation of serum from 10-day pregnant mice by size exclusion chromatography indicated the absence of high mol wt forms of mPL-I in the circulation.

Targeted Expression of Placental Lactogen in the Beta Cells of Transgenic Mice Results in Beta Cell Proliferation, Islet Mass Augmentation, and Hypoglycemia

“…To measure islet mPL-I content, islets were isolated from normal and transgenic pancreata as described (25). Murine PL-I concentration in islet extracts was measured using an mPL-I RIA as described previously (16). The detection limit of the mPL-I RIA in islet extract buffer is 1.0 ng/ml.…”

“…Normal pregnant female mice at gestational days 10 -12 were used as positive controls for detection of mPL-I in plasma. Murine PL-I was measured using an mPL-I RIA with a detection limit in plasma of 4.5 ng/ml as described previously (16).…”

Stress Induces AMPK-Dependent Loss of Potency Factors Id2 and Cdx2 in Early Embryos and Stem Cells

“…In preparation for implantation, blastocysts express high levels of mRNA for Id2 and after implantation, greatly upregulate Hand1 [29] and downregulate Id2 and Cdx2 in differentiating cells. After implantation, Hand1 in mouse placental cells [19,30] activates the PL1 promoter resulting in detectable PL1 in maternal blood by E6.0 of gestation [31]. For Hand1 to induce PL1 in differentiated cells, the dominant negative transcription factor Id2 must be lost in placental cells [30].…”

Placental-specific expression from the mouse placental lactogen II gene promoter.

“…Since PL-I and PL-II achieve much higher serum concentrations than PRL, they effectively replace PRL in pregnant mice from middle through late gestation. A peak level of mPL-I protein in serum is achieved transiently at day 10 of pregnancy; the amount of serum mPL-I then declines rapidly, although low levels of this hormone persist throughout gestation (11). Production of mPL-II is slightly delayed with respect to mPL-I, but this hormone is the major lactogenic hormone in the serum throughout the latter half of gestation (4).…”