Date of Award:

5-1-1995

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Toxicology

Committee Chair(s)

William A. Brindley

Committee

William A. Brindley

Committee

Raghubir P. Sharma

Committee

Joseph K. K. Li

Committee

Luz Colon-Teicher

Abstract

The retinoic acid receptors (RARs) constitute a group of nuclear proteins that belong to the steroid and thyroid-hormone receptor superfamily. They act as ligand-inducible transcriptional regulatory factors and provide a model for the molecular mechanism of action of retinoids (vitamin A derivatives). The objective of this study was to identify one or more isoforms of the retinoic acid receptor β (RARβ) in hamster embryos, and to study their expression during development and after retinoic acid (RA) treatment. Total RNA was extracted from a 12-day-old hamster embryo, reverse transcribed and tailed with dGTP. The resulting cDNA was subjected to anchored-polymerase chain reaction (anchored-PCR) using specific primers for hamster RARβ (hamRARβ). The final products were cloned and sequenced, and a new isoform was found that shares the last stretch of 5' untranslated region (5'-UTR) with hamRARβ2 and, by analogy with mouse, was named hamRARβ4. The existence of this new isoform in hamster was further confirmed by PCR. Using the RT-PCR technique, we studied the expression of hamRARβ2 and β4 in hamster embryos at different stages during development. The level of expression of both isoforms increased after day 8 and declined after day 11, reaching a low level at days 14 and 15. This is evidence for regulation of expression during development. Using the same technique, we also studied the effect of maternal treatment with teratogenic doses of retinoic acid in the expression of hamRARβ2 and β4 in the hamster embryo. An increase in the levels of both transcripts occurred shortly after treatment, and was followed by a subsequent decrease to normal levels after ~ 12 h. This is evidence that the RA treatment: had an effect in the expression of both isoforms, and that both have a responsive element for RA. With respect to the relative abundance of both isoforms, all the studied samples indicate that hamRARβ2 transcripts are more abundant than hamRARβ4 in whole embryos.

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