Localization of luteinizing hormone β-mRNA by in situ hybridization in the sheep pars tuberalis

The localization of luteinizing hormone beta (LH beta)-mRNA was studied by in situ hybridization in the pars tuberalis of sheep using a homologous sheep double-stranded 32P- or 35S-cDNA. The labelled cDNA probe detected one mRNA sequence in the pars tuberalis by Northern blot analysis; this sequence was similar to that detected in the pituitary. In situ, the labelling of LH beta-mRNA in the horizontal and sagittal tissue sections was found throughout the pars tuberalis. This labelling was prevented by adding an excess of cold probe or treating the sections by ribonuclease before in situ hybridization. Controls showed a labelling in the pars distalis, but not in the median eminence, hypothalamus, cerebral cortex and liver sections. Double labelling by in situ hybridization followed by immunohistochemistry using a specific LH beta-antiserum indicated that the labelling of LH beta-mRNA appeared more intense in LH-containing cells that were found only in the ventral part of the pars tuberalis. These results suggest that the entire pars tuberalis is able to produce the LH beta subunit, but that the level of translation greatly varies according to the location of the cells.