The mouse homeoprotein mLIM-3 is expressed early in cells derived from the neuroepithelium and persists in adult pituitary.
LIM-homeodomain proteins are important in cell lineage specification and possibly mediate transcriptional processes in eukaryotes. During the screening of a mouse pituitary cDNA library, we isolated a partial cDNA coding for a novel gene product that exhibited a predicted amino-terminal sequence similar to the homeobox of LIM-homeodomain-containing proteins. Reverse transcriptase-polymerase chain reactions (RT-PCR) performed on mouse pituitary mRNA using degenerate oligonucleotides based on the conserved LIM-domain sequences, allowed the extension of the 5' end of the sequence. The composite 2.2-kb cDNA structure predicts a 400-amino-acid-long novel mouse (m) protein, called mLIM-3. This name was chosen since within the 59-amino-acid homeodomain, it exhibits 97% sequence identity to a recently reported Xenopus homologue xLIM-3. The gene coding for mLIM-3 maps to the murine chromosome 2, most probably within the 2B band. Based on sequence characteristics, we suggest that LIM-3 belongs to a distinct subfamily of LIM-containing homeoproteins. Ontogeny studies using in situ hybridization demonstrated that mLIM-3 transcripts can be detected on embryonic day 11 (e11) in the primordium of the hypophysis. Following a maximum between e12 and e14, lower levels persisted into adulthood, where mLIM-3 was expressed primarily in the anterior and intermediate lobes of the pituitary. These results were confirmed by Northern blot analysis in adult mice which revealed a 2.4-kb pituitary mRNA transcript. mLIM-3 transcripts were also detected in pituitary cell lines such as the somatotrophs GH3 and GH4C1, the gonadotroph alpha T3-1, and the corticotroph AtT-20 cells, but not in 20 other cell lines derived from peripheral, endocrine, and neural tissues. Starting from e11, we also observed a transient expression of mLIM-3 in the ventral part of the spinal cord, pons, and medulla oblongata, reaching a maximum at e13 and from p7 onward, the expression of this transcript is no longer detectable. mLIM-3 is also expressed in the pineal gland with high levels observed at e20. These data suggest a potential role for mLIM-3 in the transcriptional regulation of certain genes during morphogenesis and/or maintenance of the differentiated state of the pituitary, motor neurons, and pineal gland.
Seidah
N G
NG
J.A. DeSève Laboratory of Biochemical Neuroendocrinology, Clinical Research Institute of Montreal, Montréal, Québec, Canada.
Barale
J C
JC
Marcinkiewicz
M
M
Mattei
M G
MG
Day
R
R
Chrétien
M
M
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002490:Central Nervous System / Q000196:embryology / Q000378:metabolism; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics*; D005314:Embryonic and Fetal Development; D004848:Epithelium / Q000378:metabolism; D005260:Female; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics*; D060850:LIM-Homeodomain Proteins; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D010902:Pituitary Gland / Q000196:embryology / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors
D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D060850:LIM-Homeodomain Proteins; C094898:Lhx3 protein; D012333:RNA, Messenger; D014157:Transcription Factors