Upstream AUGs in embryonic proinsulin mRNA control its low translation level.
Proinsulin is expressed prior to development of the pancreas and promotes cell survival. Here we study the mechanism affecting the translation efficiency of a specific embryonic proinsulin mRNA. This transcript shares the coding region with the pancreatic form, but presents a 32 nt extended leader region. Translation of proinsulin is markedly reduced by the presence of two upstream AUGs within the 5' extension of the embryonic mRNA. This attenuation is lost when the two upstream AUGs are mutated to AAG, leading to translational efficiency similar to that of the pancreatic mRNA. The upstream AUGs are recognized as initiator codons, because expression of upstream ORF is detectable from the embryonic transcript, but not from the mutated or the pancreatic mRNAs. Strict regulation of proinsulin biosynthesis appears to be necessary, since exogenous proinsulin added to embryos in ovo decreased apoptosis and generated abnormal developmental traits. A novel mechanism for low level proinsulin expression thus relies on upstream AUGs within a specific form of embryonic proinsulin mRNA, emphasizing its importance as a tightly regulated developmental signal.
Hernández-Sánchez
Catalina
C
Group of Growth Factors in Vertebrate Development, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu 9, E-28040 Madrid, Spain. chernandez@cib.csic.es
Mansilla
Alicia
A
de la Rosa
Enrique J
EJ
Pollerberg
G Elisabeth
GE
Martínez-Salas
Encarna
E
de Pablo
Flora
F
D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002642:Chick Embryo; D017931:DNA Primers; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D007515:Islets of Langerhans / Q000196:embryology; D051379:Mice; D009843:Oligoribonucleotides / Q000378:metabolism*; D016366:Open Reading Frames; D016133:Polymerase Chain Reaction; D011384:Proinsulin / Q000737:chemistry / Q000235:genetics*; D014176:Protein Biosynthesis / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection
D017931:DNA Primers; D009843:Oligoribonucleotides; D012333:RNA, Messenger; D011994:Recombinant Proteins; D011384:Proinsulin