Identification of two new nonclassical members of the rat prolactin family

The prolactin (PRL) family is comprised of a group of hormones/cytokines that are expressed in the anterior pituitary, uterus, and placenta. These proteins participate in the control of maternal and fetal adaptations to pregnancy. In this report, we have identified two new nonclassical members of the rat PRL family through a search of the National Center for Biotechnology Information dbEST database. The cDNAs were sequenced and their corresponding mRNAs characterized. Overall, the rat cDNAs showed considerable structural similarities with mouse proliferin-related protein (PLF-RP) and prolactin-like protein-F (PLP-F), consistent with their classification as rat homologs for PLF-RP and PLP-F. The expression of both cytokines/hormones was restricted to the placenta. The intraplacental sites of PLF-RP and PLP-F synthesis differed in the rat and the mouse. In the mouse, PLF-RP was expressed in the trophoblast giant cell layer of the midgestation chorioallantoic and choriovitelline placentas and, during later gestation, in the trophoblast giant cell and spongiotrophoblast layers within the junctional zone of the mouse chorioallantoic placenta. In contrast, in the rat, PLF-RP was first expressed in the primordium of the chorioallantoic placenta (ectoplacental cone region) and, later, exclusively within the labyrinth zone of the chorioallantoic placenta. In the mouse, PLP-F is an exclusive product of the spongiotrophoblast layer, whereas in the rat, trophoblast giant cells were found to be the major source of PLP-F, with a lesser contribution from spongiotrophoblast cells late in gestation. In summary, we have established the presence of PLF-RP and PLP-F in the rat.

Characterization of a ferritin mRNA from Arabidopsis thaliana accumulated in response to iron through an oxidative pathway independent of abscisic acid

A ferritin cDNA, AtFer1, from seedlings of Arabidopsis thaliana has been characterized. The deduced amino acid sequence of the AtFer1 protein indicates that A. thaliana ferritin shares the same characteristics as the plant ferritin already characterized from the Leguminosae and Graminacea families: (i) it contains an additional sequence in its N-terminal part composed of two domains: a transit peptide responsible for plastid targeting and an extension peptide; (ii) amino acids that form the ferroxidase centre of H-type animal ferritin, as well as Glu residues characteristic of L-type animal ferritin, are conserved in AtFer1; (iii) the C-terminal part of the A. thaliana ferritin subunit defining the E-helix is divergent from its animal counterpart, and confirms that 4-fold-symmetry axis channels are hydrophilic in plant ferritin. Southern blot experiments indicate that AtFer1 is likely to be encoded by a unique gene in the A. thaliana genome, although a search in the NCBI dbEST database indicates that other ferritin genes, divergent from AtFer1, may exist. Iron loading of A. thaliana plantlets increased ferritin mRNA and protein abundance. In contrast to maize, the transcript abundance of a gene responding to abscisic acid (RAB18) did not increase in response to iron loading treatment, and A. thaliana ferritin mRNA abundance is not accumulated in response to a treatment with exogenous abscisic acid, at least in the culture system used in this study. In addition, iron-induced increases in ferritin mRNA abundance were the same as wild-type plants in abi1 and abi2 mutants of A. thaliana, both affected in the abscisic acid response in vegetative tissues. Increased AtFer1 transcript abundance in response to iron is inhibited by the antioxidant N-acetylcysteine. These results indicate that an oxidative pathway, independent of abscisic acid, could be responsible for the iron induction of ferritin synthesis in A. thaliana.