Ontogeny And Tissue Distribution Of Iodothyronine Sulfotransferases

The expression of the different sulfotransferases is tissue- and developmental stage-dependent. Richard et al. (2001) studied the ontogeny of SULT1A1 and 1A3 in human tissues. They found high but variable hSULT1A1 expression in the fetal and postnatal human liver, which reached half the expression level of adult liver. hSULT1A3 is differently regulated: highest hSULT1A3 expression in the liver was found early in development, decreasing in the late fetal and early neonatal period, being absent in the adult liver (Richard et al., 2001). hSULT1A1 expression was also found in the fetal human brain, especially in the choroid plexus. In contrast, hSULT1A3 expression was low in the developing brain, with relatively the highest expression in cerebellum and germinal eminence (Richard et al., 2001).

RT-PCR and immunoblotting data have shown that hSULT1B1 is predominantly expressed in a wide range of adult tissues such as liver, stomach, duodenum, colon, colorectal, ovary, and cerebellum (Dooley et al., 2000); in the fetus, hSULT1B1 is only observed in the small bowel (Stanley, 2001). In contrast, although hSULT1C2 and hSULT1C4 mRNA have been found in adult kidney and ovary, respectively (Her et al., 1997; Sakakibara et al., 1998), hSULT1C2 and hSULT1C4 are mainly expressed in fetal tissues, such as small bowel, kidney, and liver (Stanley, 2001).

hSULT1E1 is expressed in the liver, mammary gland, uterus, placenta, and in a wide range of fetal tissues, such as lung, liver, adrenal, kidney, small bowel, thyroid, heart, and brain (Rubin et al., 1999; Stanley, 2001; Stanley et al., 2001; Strott, 1996). It is possible that the hSULT1E1 in the endometrium contributes to the high iodo-thyronine sulfate levels in the fetal serum and amniotic fluid (see Discussion).

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