Midkine is expressed early in rat fetal adrenal development

Adrenal gland development is complex and poorly understood at the molecular level. Only a subset of patients with adrenal hypoplasia congenita (AHC) c arry mutations in DAX1, a member of the nuclear hormone receptor superfamil y. Therefore we set out to identify other candidate genes responsible for A HC by characterizing genes involved in fetal adrenal development. To identi fy these genes, we studied the differential expression of genes in fetal ra t adrenals comparing tissues at 14 and 15 days postcoitum (dpc) since this period encompasses major morphological change in rat adrenal development. F etal rat adrenals were dissected, cDNAs were prepared, and suppressive subt ractive hybridization was performed. We isolated 126 clones of putatively d ifferentially expressed clones and approximately 250 bp of each of the clon es was sequenced. The most interesting putative developmental genes were ex amined. One member of the extracellular PTN/MDK (pleiotrophin/midkine) hepa rin-binding protein family involved in regulation of growth and differentia tion was selected for initial study. We obtained full-length transcript by 3' rapid amplification of cDNA ends and performed Northern analysis on rat adrenal RNA from fetuses at 13, 14, 15, 17, and 19 dpc and newborns. Result s from those analyses demonstrated the highest Mdk expression at days 13 an d 14 followed by a moderate decrease of expression during the fetal stages thereafter. In the newborn, Mdk expression is nearly un detectable. Our res ults indicate that Mdk has a very specific pattern of fetal expression in t he adrenals. We conclude that Mdk is involved early in fetal development of the rat adrenal. Therefore, MDK is a candidate gene for AHC not due to DAX 1 mutations. (C) 2000 Academic Press.