Low expression levels

Our studies of the ERT cell cycles show that they are regulated by nutrition (Britton Edgar 1998). If the newly hatched larva is starved for dietary amino acids, DNA replication in most ERTs is not initiated. Under starvation conditions these tissues express low levels of cyclin E and E2F, the transcription factor which is probably responsible for cyclin E expression. If either E2F or cyclin E is induced in starved larvae, DNA replication in the ERTs is activated, and thus expression of these genes appears to limit the ERT cell cycle. When nutrient-deprived larvae are fed, expression of E2F and cyclin E mRNAs increases approximately sixfold, and DNA replication is initiated in most ERT cells. If the animal is first fed and then starved, the ERT cell cycle is activated and then inactivated quite rapidly. These experiments all indicate that the ERT cell cycle is nutrition-responsive, rather than controlled by a rigid developmental program. 

Garzon, M., Vaughan, R.A., Uhl, G.R., Kuhar, M.J., Pickel, V.M. Cholinergic axon terminals in the ventral tegmental area target a subpopulation of neurons expressing low levels of the dopamine transporter. J. Comp. Neurol. 410 197, 1999. 

Low expression of a 4kb transcript was detected in uncloned cells of Myl-D7 and in all stroma-dependent subclones. Two types of secreting mutants were identified. About half of the secretors (7/16), expresses ectopically high levels of CSF-1 transcripts (e.g. 5i-l, 5i-3, 61-2, 61-3, 6i-4). The remainder of the secretors expressed low levels of CSF-1 transcripts, comparable to the very low level of CSF-1 message in wild type Myl-D7 (e.g. 6i-5, 61-21, 61-22, 61-26). 

In summary, we show that the secretory mutants can be divided into two types, mutants expressing ectopically high levels of CSF-1 mRNA that probably secrete CSF-1 and other mutants that express low levels of CSF-1 mRNA that may not release CSF-1 but instead other factors that stimulate Myl-D7 proliferation (Heberlein et al, 2006). 

A similar phenomenon has also been reported in B cells derived from chronic lymphoid leukemia (CLL) patients in which mFas is deficient or defective. Fresh de novo CLL cells, which express low levels of mFas, are resistant to agonistic anti-Fas mAb-mediated apoptosis, while CLL cells that acquire abundant mFas after short-term culture become sensitive (T4) to such induction of apoptosis. This flexibility in production of the isoforms is expected to provide a target for selective molecular therapy of tumors on the basis of manipulating decoy action of sFas. 

Frederiksen KS, Abrahamsen N, Cristiano RJ, Damstrup L, Poulsen HS (2000) Gene delivery by an epidermal growth factor/DNA polyplex to small cell lung cancer cell lines expressing low levels of epidermal growth factor receptor. Cancer Gene Ther 7 262-268... 

CDS, which are generally used as markers for helper and cytotoxic T-cells, respectively. These molecules are defined in combination with CD3+, as some other leukocytes also express these CD molecules (some macrophages express low levels of CD4 dendritic cells express high levels of CDS). HIV binds CD4 and a chemokine receptor on the surface of a T-helper cell to gain entry. The number of CD4 and CDS T-cells in blood is often used to monitor the progression of HIV infection. 

B cells express low levels of the CD80 and CD86 costimulatory molecules, which are important for the activation of naive T cells. Indeed, resting B cells do not adequately activate naive T cells and induce tolerance rather than immunity [123, 124],... 

HMG-CoA reductase activity and LDL receptor levels always appear to change in the same direction in cells exposed to different levels of LDL. Similarly, a mutant line of Chinese hamster ovary (CHO) cells exposed to delipidated serum expresses low levels of both HMG-CoA reductase and LDL receptor activities compared to normal cells [88], Taken together, this evidence suggests coordinate expression of these two activities. 

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