Changes in UsnRNA biosynthesis during rat liver regeneration

Abstract

Partial hepatectomy (P.H.) induces a partially synchronized growth response of liver under normal regulation of growth. In this phase changes in cellular morphology, radial distribution pattern of cells and other biological as well as major biochemical changes are well documented [24]. Here, we have shown that the cellular content of UsnRNAs altered during this proliferative phase as well. The level of spliceosomal UsnRNAs (U1, U2, U4-U6) gradually decreased by 30-50 % upto 48 hrs of RH. followed by gradual increase to reach the normal level within one month of R H. The U3 snRNA level on the other hand, was nearly equal to that in normal liver at 48 hrs of RH. but in 24 and 72 hrs of RH. its level was high (4 fold) in contrast to that in other UsnRNAs. Thus, it is clear from our data that the level of all the six UsnRNAs decreased during 48 hrs of RH. compared to that after first 24 hrs. This has been correlated in the kinetics of UsnRNAs' synthesis (in terms of labelling) in isolated hepatocytes, where the rate of labelling of all the six UsnRNAs increased 20-30% in 24 hrs regenerating hepatocytes (R.H.) followed by sharp decrease by 30-50% within next 24 hrs, compared to that in the normal hepatocytes. But from 72 hrs onwards in R.H. the rate of labelling of all the six UsnRNAs again increased by 30-50% (compared to that in normal hepatocytes) followed by decrease of their labelling-rate to reach the normal level in R.H. within one month of RH. Thus, it may be concluded that the changes in UsnRNAs' level during th e proliferative phase of liver regeneration may be either due to the alteration in the rate of synthesis (in terms of labelling) or along with it differential turn over rate; this phenomenon may have some consequences with the regenerative process of liver. (Mol Cell Biochem 141: 71-77, 1994).

Involvement of SRD2‐mediated activation of snRNA transcription in the control of cell proliferation competence in Arabidopsis

“…However, expression of snRNA genes appears not to be static but to be regulated dynamically, as different tissues contain different kinds of snRNA at different levels (Ray et al, 1997). A close relationship between changes in snRNA levels and specific developmental phenomena, such as liver regeneration and myoblast differentiation in rats, has been reported (Glibetic et al, 1992;Ray et al, 1994). This work may provide some clues to the possible role of snRNA transcriptional control, although this must be investigated further.…”

“…A close relationship between changes in snRNA levels and specific developmental phenomena, such as liver regeneration and myoblast differentiation in rats, has been reported (Glibetic et al. , 1992; Ray et al. , 1994).…”

Differential alterations in metabolic pattern of the spliceosomal uridylic acid‐rich small nuclear RNAs (UsnRNAs) during malignant transformation of 20‐methylcholanthrene‐induced mouse CNCI‐PM‐20 embryonic fibroblasts

“…It is evident from our study that, both RNA polymerase II and III transcribed spliceosomal UsnRNAs are differentially regulated during MCA‐induced transformation. The differential metabolic pattern of the spliceosomal UsnRNAs seen in our study is not similar to that seen in rat liver regeneration due to partial hepatectomy 15 or during the development of rat from embryonic to neonatal stage 16, indicating a difference in the metabolic pattern of UsnRNAs in carcinogenesis when compared to normal proliferation and development. However, the observations from this study are corroborative with our previous reports on UsnRNA expression pattern in BaP‐induced lung carcinogenesis where there was a significant increase in the level of U4 (∼2.5‐fold) and U5 (∼2‐fold) in the dysplastic lung lesions, indicating their probable role in tumorigenesis 29.…”

“…Although the five major UsnRNAs are metabolically stable, quantitative alterations in their metabolic pattern have been observed during induced cellular proliferation, differentiation, tissue regeneration, and embryonic development, indicating the importance of these genes in these cellular processes 11–18. For example, the following has already been reported: (a) a preferential expression of certain forms of U1snRNA during mouse embryo development, (b) malignant transformation activity of U5, (c) differential accumulation of U1 and U4 snRNA, and (d) overexpression of U6 snRNA during embryogenesis in Xenopus .…”

Molecular Regulation of Liver Regenerationa

“…During liver regeneration following PH the efficiency of processing hnRNA into mature mRNA is increased coincident with increased steady‐state cytoplasmic mRNA levels 70 . Moreover, following PH, modulation in the biosynthesis of the spliceosomal UsnRNAs involved in splicing the hnRNAs is observed 71 . Furthermore, one of the novel insulin‐induced delayed‐early genes identified in hepatocytes is a regulator of alternative pre‐mRNA splicing 39 and fibronectin transcripts are alternatively spliced in quiescent versus regenerating liver 72 .…”