Rodents possess an expanded prolactin (PRL) family of genes. These genes encode for a family of structurally related hormones/cytokines that are expressed most prominently in the anterior pituitary, uterus and placenta. In this study, we have identified a new member of the rat PRL family through a search of the National Center for Biotechnology Information expressed sequence database. The cDNA was sequenced and its corresponding mRNA characterized. On the basis of existing nomenclature, the rat cDNA was termed PRL-like protein-N (PLP-N). PLP-N has structural features indicative of its inclusion in the PRL family and is most closely related to PRL-like protein-F (PLP-F) and proliferin related protein (PLF-RP). A survey of PLP-N mRNA expression by Northern analysis indicated that PLP-N showed extensive expression in the metrial gland and minimal expression in the chorioallantoic placenta or other tissues. Expression of PLP-N mRNA was restricted to migratory trophoblast cells. Junctional zone trophoblast cells isolated from day 13 of gestation placenta differentiated in vitro and exhibited a capacity for PLP-N expression. In summary, we have discovered a new member of the PRL family that is prominently expressed in migratory trophoblast cells residing in the metrial gland.

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Phenotypic characterization of Akt1 and Igf2 null mice has revealed roles for each in the regulation of placentation, and fetal and postnatal growth. Insulin-like growth factor 2 (IGF2) is encoded by the Igf2 gene and influences cellular function, at least in part, through activation of an intracellular serine/threonine kinase called AKT1. Akt1 and Igf2 null mice were originally characterized on inbred and mixed genetic backgrounds, prohibiting direct comparisons of their phenotypes. The impact of loss of AKT1 or IGF2 on placental, fetal, and postnatal function were examined following transfer of Akt1 and Igf2 null mutations to an outbred CD1 genetic background. Disruption of IGF2 did not affect AKT expression or activation. Both Akt1−/− and Igf2−/− mice exhibited decreased placental weight, fetal weight and viability. Deregulation of placental growth was similar in Akt1 and Igf2 nulls; however, disruption of Igf2 had a more severe impact on prenatal survival and postnatal growth. Placental structure, including organization of junctional and labyrinth zones and development of the interstitial, invasive, trophoblast lineage, were similar in mutant and wild-type mice. Akt1 and Igf2 null mutations affected postnatal growth. The relative impact of each gene differed during pre-weaning versus post-weaning growth phases. AKT1 had a more significant role during pre-weaning growth, whereas IGF2 was a bigger contributor to post-weaning growth. Akt1 and Igf2 null mutations impact placental, fetal and postnatal growth. Placental phenotypes are similar; however, fetal and postnatal growth patterns are unique to each mutation.

The objective of this study was to examine ultrastructural aspects of bovine in uiiro-produced blastocysts associated with cryopreservation by vitrification. Morphologically good embryos were used and treated with ethylene-glycol-based vitrification solution (VS). The untreated embryos had conventional fine structure. The post-warming embryos treated with direct exposure to VS (one-step procedure) showed cellular damage structurally by cryopreservation, which included loss of microvilli, disruption of the plasma membrane, mitochondrial changes and swelling of the endoplasmic reticulum. However, nuclei and junctional regions seemed to be resistant to cryoinjury. In contrast, the post-warming embryos pre-equilibrated with 10% ethylene glycol for 5 min and subsequent exposure to VS (two-step procedure) showed less damage than those treated by the one-step procedure. Postwarming embryos treated by the two-step procedure were cultured in vitro for 18 h. Some embryos survived and their structures re-formed to the former state, while other embryos showed serious injuries and could not reconstitute the blastocoele. Three post-warming embryos treated by the twostep procedure that survived after in vitro culture were transferred to three recipients and one of these resulted in pregnancy. These results indicate that cryopreservation by vitrification can damage membranous structures of the cells of bovine embryos, the extent and nature of this damage being dependent on the vitrification procedure.