Spatial and temporal expression of the cystathionine beta-synthase gene during early human development

We report the cystathionine-beta synthase (CBS) gene expression pattern dur ing early human embryogenesis (3 to 6 weeks post conception) by in situ hyb ridization and in fetal and adult tissue by Northern Blot analysis. Probes were chosen to recognize either the common sequence to all known CBS mRNAs or the sequences of two different major exons 1 issued of we have previousl y identified. We demonstrate by in situ hybridization that CBS is continuou sly expressed from the earliest stages studied (22 days post conception) du ring embryogenesis in the tissues of developing embryos which will after bi rth present clinical abnormalities in homocystinuria patients. It is expres sed at an especially high level in the neural and cardiac systems until the liver primordium appears. In embryonic central nervous system, the whole n eural tube and primary brain vesicles are labeled. Secondary brain vesicles labeling are dependent on the neuroepithelium differentiation. The ventric ular layer of the rhombencephalon, cranial nerve nuclei and then after cere bellar cortex derived from rhombencephalon ventricular layer are strongly l abeled. Thalamus and other derivatives of the diencephalon plate, the neuro blastic layer of the retina, lens and dorsal root ganglia are labeled. Afte r 35 days post conception, CBS mRNAs was detected in endocardial cells and in cells derived from the neural crest of the heart and in particular devel oping mesodermic regions such as the primitive hepatocytes of the liver, me sonephros vesicles, various endocrine glands and developing bones. We could not detect tissue specificity of different probes at this embryonic stage. Northern blot analysis consistently detected mRNA species in fetal 25 week s post conception brain, liver and kidney. The common cDNA probe revealed t he 2.5 and 3.7 kb mRNA species from brain, liver and kidney. The exon Ib pr obe detected only the 2.5 kb mRNA and the exon Ic probe the 3.7 kb mRNA in these three tissues. In adult tissue, the Ib probe detected only the 2.5 kb mRNA and the Ic probe only the 3.7 kb mRNA in the liver. (C) 1999 Academic Press.