ABSTRACT
A novel transmembrane protein (designated X7365) containing two follistatin modules and an epidermal growth factor (EGF) domain has been described in the hypothalamic-pituitary axis of Xenopus laevis. We have now cloned the highly conserved mouse orthologue (M7365), and its mRNA was detected in many mesodermal and (neuro)ectodermal tissues in 8.5-day-old mouse embryos. During further development, M7365 mRNA expression became restricted to certain regions in the brain and to ganglia. In the adult mouse, the brain is the major site of M7365 expression.
Subject(s)
Epidermal Growth Factor/genetics , Glycoproteins/genetics , Membrane Proteins/genetics , Neoplasm Proteins , Xenopus Proteins , Amino Acid Sequence , Animals , Base Sequence , Brain/embryology , Brain/metabolism , DNA, Complementary , Embryonic and Fetal Development , Follistatin , Gene Expression , Humans , Membrane Proteins/metabolism , Mice , Mice, Inbred C57BL , Molecular Sequence Data , Protein Structure, Tertiary , RNA, Messenger , Sequence Homology, Amino Acid , Xenopus laevisABSTRACT
To convert animal pole cells of a frog embryo from an ectodermal fate into a neural one, inductive signals are necessary. The alkalizing agent NH4Cl induces the expression of several anterior brain markers and the early pituitary marker XANF-2 in Xenopus animal caps. Here it is demonstrated that NH4Cl also induced proopiomelanocortin (POMC)-expressing cells (the first fully differentiated pituitary cell type) in stage 9 and 10 Xenopus animal caps, and that all-trans retinoic acid, a posteriorizing agent, was able to block this induction when it was administered within 2 h after the start of NH4Cl incubation. Thus, after 2 h, the fate of Xenopus animal cap cells was determined. Microinjection of ribonucleic acid (RNA) encoding noggin, an endogenous neural inducer, led to the induction of POMC gene expression in animal caps of stage 10 embryos, suggesting that noggin represents a candidate mesodermal signal leading to the POMC messenger (m) RNA producing cell type in uncommitted ectoderm. Hence, an alkalizing agent and a neural inducer can generate a fully differentiated POMC cell lineage from Xenopus animal caps.
Subject(s)
Embryo, Nonmammalian/metabolism , Pro-Opiomelanocortin/genetics , RNA, Messenger/biosynthesis , Xenopus laevis/embryology , Ammonium Chloride/pharmacology , Animals , Carrier Proteins , Cell Differentiation/drug effects , Cell Lineage/drug effects , Cell Lineage/physiology , DNA Primers/chemistry , Ectoderm/physiology , Female , Gene Expression , Homeodomain Proteins/drug effects , Homeodomain Proteins/genetics , Mesoderm/physiology , Microinjections , Nervous System/embryology , Pro-Opiomelanocortin/biosynthesis , Proteins/metabolism , Reverse Transcriptase Polymerase Chain Reaction , Signal Transduction , Tretinoin/pharmacologyABSTRACT
The production of peptide hormones through proteolytic cleavage of prohormones, e.g., proopiomelanocortin (POMC), involves a number of regulated secretory proteins, such as prohormone convertase PC1, PC2 and granin family members, that are co-expressed with the prohormone. Although the expression of these proteins has been well-studied in adult animals, data on their expression during development are limited. We used whole-mount in situ hybridization to visualize POMC mRNA expression in the intermediate and anterior pituitary of Xenopus tadpoles. A more sensitive analysis, namely semi-quantitative reverse-transcription polymerase chain reaction (RT-PCR) on total RNA isolated from Xenopus developmental stages, revealed that the expression of POMC, PC1 and PC2 mRNA commenced at stages 13 (neural plate stage), 15 (neural fold stage) and 19 (neural tube stage), respectively, with a gradual increase in their expression levels during further development. Surprisingly, and in contrast to what holds for POMC and the convertases, mRNAs for secretogranin II and III (SgII, SgIII) and 7B2 were not only expressed during neural development, but could already be detected in unfertilized mature oocytes, the first cleavage stages and in blastula-stage embryos. These granins are thus maternally present in Xenopus embryos suggesting that they may have a role during oogenesis and/or early embryonic development.
