In eukaryotic cells, functional macromolecules such as protein and RNA traverse the nuclear envelope, thus permitting communication between the nucleus and the cytoplasm. The molecular mechanism of the nucleocytoplasmic transport has been extensively studied and considerable knowledge concerning its fundamental machinery has been accumulated. That is, it has been shown that importins (karyopherins) function as a receptor/carrier molecule of nuclear localization signal (NLS)-containing karyophilic proteins and that a small GTPase Ran acts to assure the directionality of the transport through the nuclear pore complexes (NPCs). In addition, the subject of how many transport factors/pathways exist in cells to carry a variety of karyhophiles into the nucleus has been examined. In this article, we focus on the molecular divergence of the nucleocytoplasmic transport pathways and review some recent findings on the issue of multiplicity, which has been examined using intracellular signaling molecules such as STAT (signal transducer and activator of transcription) and Smad as transport substrates.
The adrenal cortex consists of three zones producing different hormones: zona glomerulosa (zG), zona fasciculata (zF) and zona reticularis (zR). Accumulated knowledge has revealed the contribution of transcriptional factors to the functional development of the adrenal cortex, however, the regulatory mechanisms have not yet been fully understood. We studied the expression and localization of transcriptional factors, SF-1, GATA4 and GATA6 by immunohistochemistry in the developmental process, establishing three zones of the rat adrenal cortex. The development of the adrenal cortex was monitored by the expression of cortical enzymes, P45011β, P450aldo, and P450scc on gestational days 15, 16, 18, 19, 20 (G15, G16, G18, G19, G20) and postnatal days 1, 2, 20 (P1, P2, P20) in Spraque-Dawley rats. GATA4 expression was observed in a limited number of cortical cells from early gestation (G15) to the neonatal period (P20) before complete establishment of the cortical zones. Nearing the final phase of zG establishment (P20), GATA4 changed its intracellular localization from the nuclei to the perinuclear region. Another noteworthy finding is that GATA6 translocated from the cytoplasm into the nuclei on G19, followed by a leaning distribution of SF-1 in zG (P1) and changing the distribution of SF-1 from zG to zF parallel to the establishment of zG (P20). In conclusion, we report that GATA4 was detected in the immature phase of the adrenal cortex in limited expression but diminished in the mature adrenal cortex. GATA4 may participate in the gene transcription required for the development of the adrenal cortex.
Germ cell death is very common in mammalian testis, during both early testicular development and in the adult period, however the molecular mechanisms underlying the induction of germ cell apoptosis in mouse testes are largely unknown. The aim of this study was to investigate the possible involvement of Bcl-2 and Bax in induction of germ cell apoptosis in immature and mature mouse testes. To gain insights into downstream molecular cascades, we examined the expression of cytochrome c and activated caspase-3. Testes of adult and neonatal mice at 0, 6, 12 and 18 days after birth were used. Germ cell apoptosis was evaluated by Terminal dUTP nick end-labeling (TUNEL) staining and the expression of apoptosis-related proteins was examined by enzyme-immunohistochemistry. TUNEL-positive germ cells appeared at 6 days after birth, reaching a maximum number at 12 days after birth, when such cells were identified as gonocytes or spermatogonia. In contrast, by 18 days, the main population of TUNEL-positive cells comprised spermatocytes and the average number of positive cells per seminiferous tubule remained nearly constant thereafter. The expression of Bcl-2 and Bax remained constant in germ cells from 0 to 12 days after birth. However, during that period we observed a dramatic redistribution of Bax staining from the cytoplasm to the whole cell including the nucleus. In parallel with the Bax redistribution, cytochrome c staining spread to the cytoplasm and activation of caspase-3 occurred. Moreover, in mirror sections of neonatal and adult testes, we confirmed a strong correlation among TUNEL-staining and Bax redistribution accompanying the cytochrome c redistribution and activation of caspase-3. The temporal and spatial association of Bax and spatial apoptosis-related protein expression with TUNEL-positive germ cells indicates that Bax redistribution may be a trigger for the induction of germ cell apoptosis in mouse testes.
We found differential expression of two neuronal markers in nerve fibers that came from the same neuronal somata. Prolactin releasing peptide (PrRP) and tyrosine hydroxylase (TH), a catecholamine synthesis rate-limiting enzyme, were differentially distributed in distinct fibers derived from the same neuronal cell body located in the rat medulla oblongata. All PrRP-immunoreactive neurons were catecholaminergic at the cell body level in the nucleus tractus solitarius (NTS) and in the ventral and lateral reticular nuclei (VLRN). However, in the terminal areas such as the bed nucleus of the stria terminalis (BNST) and paraventricular nucleus (PVN), where fibers are projected from both PrRP and TH positive neurons in the NTS and VLRN, dense PrRP immunoreactive fibers were observed that did not contain TH. In the medulla oblongata, proximal fibers near a neuronal cell body that contained both TH and PrRP were diverged into mainly PrRP-positive or mainly TH-positive fibers. These results suggest that TH and PrRP are differentially expressed between fibers from the same cell body. The fibers containing predominantly PrRP have been detected at birth, so the machinery to transport PrRP and TH separately may be established at an embryonic stage.
Macrophages (MΦs) and smooth muscle cells (SMCs) comprise atherosclerotic lesions and their migration, proliferation and foamy change are the essential steps in initiating and establishing the lesions. It is also a well-documented fact that the oxidatively modified LDLs (low density lipoproteins) play important roles involving various lipoperoxidative events in the migration and foamy change of those cells. Yet, detailed sequential cell processes in the atherosclerotic changes still remain unexplained. In the present study, the time related close spatial relationship of MΦs and SMCs in experimental rabbit atherosclerosis were histologically and immunohistochemically investigated. The MΦs' migration into the intima preceded the SMCs' migration. Migrated intimal SMCs encircle or enfold the foamy MΦs, and it appeared as if they were preventing MΦ migration. To confirm whether lipid peroxidation is involved in the migration and foamy change of MΦs or not, we performed immunohistochemical detection of the glutathione peroxidase (GSH-PO), a lipid peroxide scavenger, using the specific antibody against rabbit GSH-PO produced in our laboratory. Migrated foamy MΦs exhibited intense GSH-PO staining, suggesting the vigorous occurrence of lipid peroxidation. The cellular interaction between foamy MΦs and SMCs should be the essential factor in the pathogenesis of atherosclerosis.