Gene expression of vascular endothelial growth factor-A in the pituitary during formation of the vascular system in the hypothalamic-pituitary axis of the rat

Abstract

Techniques involving fluorescein-5-isothiocyanate-conjugated gelatin injection, immunohistochemistry, and in situ reverse transcription/polymerase chain reaction (RT-PCR) revealed a close relationship between vascular endothelial growth factor (VEGF)-A-expressing cells and microvessels in the hypothalamic-pituitary axis of the rat. In situ RT-PCR clearly indicated the presence of VEGF-A mRNA-expressing cells in the pars tuberalis and in the pars distalis both at embryonic day 15.5 (E15.5) and in later developmental stages. The primary capillaries extended along the developing pars tuberalis, whereas the portal vessels penetrated into the pars distalis at E15.5 and subsequently expanded into the lobe to connect with the secondary capillary plexus, emerging in the pars distalis. At the same time, several VEGF-A-positive cells appeared in the pars distalis. These VEGF-A-positive cells were found to correspond to a portion of adrenocorticotropin (ACTH) cells by dual-staining for in situ RT-PCR and immunohistochemistry, suggesting that some ACTH cells have the potential to produce VEGF-A. Thus, the present study suggests that VEGF-A is involved in the development of the primary capillaries and in the vascularization of the pars distalis, but not in the portal vessels since the formation of portal vessels begins at E13.5, before the appearance of VEGF-A in the rostral region of the pars distalis.

The spatial and temporal expression of delta-like protein 1 in the rat pituitary gland during development

“…Our analysis of secreted protein expressed in the rat pituitary anlage on E13.5, when the portal vessels Wrst appear in the Atwell's recess (Nakakura et al 2006), by the signal sequence trap method resulted in the identiWcation of 152 clones containing genes encoding Dlk1 from among 550-positive clones. Dlk1 is a type I membrane protein that has six EGF-like repeats in its extracellular domain, is presumed to function in the regulation of the development of pituitary hormone-secreting cells.…”

“…It is well known that many diVerent secreted proteins and transcription factors are involved in the diVerentiation of pituitary hormone-secreting cells (Zhu et al 2007) and the architecture of the vascular system and neuronal network of pituitary glands (Nakakura et al 2006(Nakakura et al , 2007. Our analysis of secreted protein expressed in the rat pituitary anlage on E13.5, when the portal vessels Wrst appear in the Atwell's recess (Nakakura et al 2006), by the signal sequence trap method resulted in the identiWcation of 152 clones containing genes encoding Dlk1 from among 550-positive clones.…”

“…The pars intermedia (PI), on the other hand, is under the direct control of dopaminergic (DA) neurons arising in the periventricular nucleus (PeV) and arcuate nucleus in the hypothalamus (Goudreau et al 1992(Goudreau et al , 1995. We previously reported that vascular endothelial growth factor-A is involved in the formation of the primary capillaries and in the vascularization of the PD (Nakakura et al 2006), and that brain-derived neurotrophic factor plays a role directing the elongation of DA neurons from the PeV to the PI (Nakakura et al 2007). However, it has yet to be fully clariWed how molecular and cellular mechanisms are involved in the architecture of the vascular system and neuronal network in the hypothalamus pituitary axis.…”

“…In the study reported here, we extensively analyzed secreted proteins by the signal sequence trap method (Kitamura et al 1995;Kojima and Kitamura 1999) using the cDNA library of the rat pituitary anlage on embryonic day (E) 13.5, when the formation of the portal vessels starts (Nakakura et al 2006). We cloned a number of delta-like protein 1 (Dlk1) cDNAs that have been previously reported by Hansen et al (1998).…”

Localization of vascular endothelial growth factor (VEGF) receptors in normal and adenomatous pituitaries: detection of a non-endothelial function of VEGF in pituitary tumours

“…In normal pituitary, both folliculostellate (FS) cells and endocrine cells were identified as sources of VEGF (Gospodarowicz et al 1989, Jabbour et al 1997, Fan & Iseki 1998, Gloddek et al 1999, Renner et al 2002, Cristina et al 2005, Nakakura et al 2006. In human pituitary adenomas, tumour cells synthesize and release VEGF-A (Lloyd et al 1999, Iuchi et al 2000, Lohrer et al 2001, McCabe et al 2002, Fukui et al 2003, Viacava et al 2003, Onofri et al 2004.…”