Identification Of Novel Isoforms Of Midkine And Their Corresponding Novel RNA Splicing

Midkine (MK) is a heparin-binding growth/differentiation factor. It is an early responded gene under retinoid acid induction during mouse embryogenesis. MK has been shown to be involved in a variety of biological processes, such as growth, differentiation, angiogenesis and apoptosis. It not only plays a role in embryogenesis but also is closely related to tumorigenesis/carcinogenesis.To study the expression and function of MK during organogenesis and tissue differentiation, we examine the spatial expression of MK in mouse embryogenesis by immunohistochemistry. It turns out that during (pancreas & kidney) tissue differentiation, MK is concentrated on the epithelial-mesenchymal interface especially at the areas proximal to the nascent blood vessels and its expression level decreased with the cellular differentiation/maturity, i.e., its expression level peaked at the stem basal membrane of the undifferentiated cells and attenuated with the differentiation of cells. These expression patterns imply its function in the ubiquitous epithelial/mesenchymal interactions in organogenesis and tissue differentiation, in the signaling pathway in the recent identification of nascent blood vessel induction of tissue differentiation as well as in the regulation of the balance of stem cell self-renewal/proliferation vs differentiation.We further investigate MK's temporal expression during embryonic development by RT-PCR. We have applied nested-touchdown PCR strategy to increase the specificity and sensitivity of PCR. In the end, (1) we have not only found that MK expression is regulated in embryogenesis, i.e., it is significantly expressed between E6.5 and E15.5 with little expression outside this period; (2) We have also first detected the...