Detection of growth hormone, prolactin and human beta-chorionic gonadotropin messenger RNA in growth-hormone-secreting pituitary adenomas by in situ hybridization

GH-, PRL-, POMC-, beta-TSH-, beta-LH-, beta-FSH-mRNA in gonadotroph adenomas of the pituitary by in situ hybridization in comparison with immunostaining and clinical data

In situ hybridization (ISH) enables the visualization of specific mRNA for pituitary hormones. Our collection consists of 40 surgically removed pituitary adenomas that were classified as follicle stimulating hormone/luteinizing hormone (FSH/LH) cell adenomas by structure and by immunostaining (IH) for all pituitary hormones. All forty adenomas were regarded as clinically inactive. The aim of our study was to examine nonfunctioning adenomas by ISH for demonstration of mRNAs for all pituitary hormones. The results were compared with proliferation markers, invasiveness and clinical data. ISH detected signals for all pituitary hormones at a range of 30% for prolactin (PRL) to 85% for proopiomelanocortin (POMC). mRNA for beta-FSH was detected in 70% and beta-LH mRNA in 43% of adenomas. Thirty-three percent of adenomas revealed negative mRNA detection for beta-LH but positive hormone content. The majority of adenomas (75%) expressed more than two mRNAs simultaneously, mostly the combination of POMC mRNA together with beta-FSH mRNA and one to four others. Comparison with clinical data showed no significant differences except for one adenoma with a high Ki-67 index (> 2.1% positive nuclei). This adenoma showed very high signals for PRL and beta-TSH mRNA.

Organization and expression of bovine TSPY

We have isolated genomic sequences as well as transcripts from the bovine homolog of the human testis-specific protein, Y-encoded, TSPY which-in both species-is located on the Y Chromosome (Chr), organized as a gene family with a variable number of members, and expressed exclusively in the testis. 1266 bp of bovine TSPY specific sequence have been isolated from a testis cDNA library, by RT-PCR analyses and by Rapid Amplification of cDNA Ends (RACE). A bovine TSPY gene 4 is organized in seven exons, and transcripts are polyadenylated at various 3' ends. Consensus polyadenylation signals AAUUAAA are missing. Microheterogeneous sequence variation is found between TSPY family members. In addition, homologies to other Y-located repeated sequence families, BRY, have been discovered; these sequences are presumably derived from ancient members of the TSPY cluster, now forming a separate, probably nonfunctional subfamily. Bovine TSPY is subject to differential splicing. In the adult, it is expressed in early germ-cell stages, and expression could also be detected in fetal testis. Comparison with the human homolog shows the highest degree of similarity in the coding regions of exons 2, 3, and 4, which are also precisely conserved regarding their length.

Molecular Pathology of the Pituitary Adenomas

Molecular techniques have been applied to the study of pituitary adenomas by many investigators. We have used nonisotopic in situ hybridization (ISH) to analyze pituitary adenomas in our laboratory. These studies have provided insight into mRNA production by various adenomas, and have contributed toward our new proposed clinical and cytofunctional classification of pituitary adenomas.

Expression of plurihormonal mRNAs in somatotrophic adenomas detected using a nonisotopic in situ hybridization method: comparison with lactotrophic adenomas

We used a nonisotopic in situ hybridization (ISH) method to investigate the expression of pituitary hormone, including glycoprotein hormone mRNAs in 17 somatotrophic and four lactotrophic adenomas. Our ISH studies of lactotrophic adenomas showed that their hormonal gene expression was confined to prolactin, whereas those of somatotrophic adenomas showed that some of them expressed plurihormonal genes. In some somatotrophic adenomas that were immunohistochemically negative for pituitary hormones, positive reactions, mainly for adrenocorticotropic hormone (ACTH), follicle-stimulating hormone beta subunit (FSH beta), and luteinizing hormone beta subunit (LH beta) mRNAs, were observed in our ISH studies. These results suggest that some somatotrophic adenomas may originate from plurihormonal primordial stem cells, which we have presumed serve as precursors for various hormone-expressing cells. It is unclear why some somatotrophic adenomas derived from plurihormonal primordial stem cells manifest clinically only as the acromegalic hyperfunction syndrome or gigantism. Additional translational factors or some other somatic mutations may play important roles in the clinical manifestations of such adenomas. In conclusion, some somatotrophic adenomas appear to be derived from plurihormonal primordial stem cells, whereas lactotrophic adenomas are well differentiated tumors that originate from lactotrophic cells, which represent the final stage of acidophilic cell line differentiation.

Amyloid Deposits in Pituitaries and Pituitary Adenomas: Immunohistochemistry and In Situ Hybridization

The patterns of deposition and immunoreactivity of interstitial amyloid were studied in 11 pituitary glands obtained at autopsy and 9 surgically resected pituitary adenomas using Congo red staining and a panel of antisera directed against 5 major amyloid fibril proteins and all pituitary hormones. The deposition pattern of amyloid in pituitary glands differed from that in adenomas but all amyloid deposits showed an immunostaining with anti-amyloid X-light chain. The remaining antisera were immunonegative. In situ hybridization using an oligodeoxyribonucleotide-probe complementary to the mRNA coding for the constant region of human X-light chain yielded no hybridization signals in the pituitaries or pituitary adenomas, excluding local synthesis and secretion of immunoglobulins. Since no case studied suffered from generalized AX-amyloidosis and adsorption of immunoglobulins to the unknown amyloid fribril protein of the pituitary seems to be unlikely, crossreaction of the polyclonal antisera with an undefined antigen is probable. The similar immunostaining properties of amyloid deposits in "normal" pituitaries and pituitary adenomas suggest they both originate from the same precursor protein.

Comparison of in situ hybridization and immunocytochemistry for the detection of residual beta cells in the pancreas of streptozotocin-treated diabetic rats

The relative efficacy of immunocytochemistry versus in situ hybridization in identifying residual beta cells was studied in rats with streptozotocin-induced diabetes. Consecutive sections of pancreas of streptozotocin-treated diabetic rats and control animals were alternately subjected to in situ hybridization (synthetic oligonucleotides complementary to rat preproinsulin mRNA) and immunocytochemistry (monoclonal antibodies to insulin). The results obtained with both methods were quantitated with the use of computer-assisted image analysis, and the ratio of cells positive by immunocytochemistry to those positive by in situ hybridization was determined. Under normoglycaemic conditions the values obtained by immunocytochemistry correlated well with those obtained by in situ hybridization (immuno/in situ > 95%). In the streptozotocin diabetic animals, however, immunocytochemistry resulted in a distinct underestimation of the number of residual beta cells (immuno/in situ < 80%). This difference was even more striking in small islet cell clusters (< 100 microns) (immuno/in situ 20%). These results suggest that in situ hybridization for prohormone mRNA is the method of choice for the identification of residual or regenerating beta cells with very low insulin content. Caution should be used when interpreting quantitative data in diabetic conditions that are based exclusively on immunocytochemical detection methods.