The these terms are not well defined, and their meaning is only understandable from the context in which they are used.

For instance, there is clearly nothing like "gene expression" (despite the fact that this term is frequently used - everywhere). Genes can be more or less active (better: actively transcribed), so that their information is expressed in some form of RNA. If this RNA is mRNA and this is translated into proteins, the gene information is expressed into a protein, and it may eventually be expressed into some phenotype.

Taking "expression" (no matter if as "mRNA expression" or "protein expression") as the amount of produced product is also not clear from the word alone. Is it the rate with which (nascent? ripe?) molecules are produced, or is it the amount or concentration of these molecules in a (current) turn-over state of production and destruction? These can be very different things with very different biological meanings. It may be that the actual transcription (or translation) rate is much higher (of the molecule half-life is very short) or much lower (if the half-life is very long). Very often, only the amounts or concentrations of molecules are measured, so the values reflect a turn-over state. We can then only hope that changes in these values reflect changes in transcriptional or translational activity - but we must be aware that such changes can also be caused by a change in the stability of the product (for some proteins also an induced secretion can lead to a lower protein concentration - a lower "protein expression").

I think there is no problem using simple or sloppy terms like "gene expression", as long as we are aware of and understand the context.

The these terms are not well defined, and their meaning is only understandable from the context in which they are used.

For instance, there is clearly nothing like "gene expression" (despite the fact that this term is frequently used - everywhere). Genes can be more or less active (better: actively transcribed), so that their information is expressed in some form of RNA. If this RNA is mRNA and this is translated into proteins, the gene information is expressed into a protein, and it may eventually be expressed into some phenotype.

Taking "expression" (no matter if as "mRNA expression" or "protein expression") as the amount of produced product is also not clear from the word alone. Is it the rate with which (nascent? ripe?) molecules are produced, or is it the amount or concentration of these molecules in a (current) turn-over state of production and destruction? These can be very different things with very different biological meanings. It may be that the actual transcription (or translation) rate is much higher (of the molecule half-life is very short) or much lower (if the half-life is very long). Very often, only the amounts or concentrations of molecules are measured, so the values reflect a turn-over state. We can then only hope that changes in these values reflect changes in transcriptional or translational activity - but we must be aware that such changes can also be caused by a change in the stability of the product (for some proteins also an induced secretion can lead to a lower protein concentration - a lower "protein expression").

I think there is no problem using simple or sloppy terms like "gene expression", as long as we are aware of and understand the context.

Hello

I agree with Jochen Wilhelm;

No problem using this term with gene or protein, as long as we are understand the meaning of use .

Good Luck

The word "expression" is very ambiguous indeed. Just to make their statement more evident people use this word without paying attention to the biological process they meant to address. The simplest answer to your question is to use the scientific terms given to gene or protein expression which are transcription and translation respectively. Try to avoid using word "expression" as far as you can.

Thanks Jochen Wilhelm for sharing your opinion. I agree with you that the meaning of the word "expression" depends on the context. But, thinking of the semantics of the word (expression), I feel uncomfortable when I use this word for referring to translation. Like Ankur Bothra says, is very ambiguous. But, it's very uncommon to read in a paper the term "translation" when is discussing how the amount of protein is affected by anything (e.g., "The A compound increase the translation of protein X significantly.").

Jeysson: Jochen did a great job getting granular, nothing to add there. I was in your position many years ago, and eventually stopped using the word "expression" to refer specifically to gene transcription. I now use it much more promiscuously. "Gene expression" or "protein expression," we all know what the author is saying...so I am forgiving, even if it lacks specificity.

Dear Ricardo, if you talk about "gene transcription", is it really what you measure? Just quantifying mRNA (with Northerns, qrtPCRs, arrays or NGS) does not measure transcription, as changes in the amounts can be caused by other processes as well.

Hi Jochen. That is absolutely true, I oversimplified, and should not have used the word “transcription”. Regardless of what caused the difference, either in RNA or protein abundace, I now simply just say “expression” for both.

No, mRNA expression is a direct consequence of transcription, whereas, protein expression may also be a result of posttranscriptional events/processing and regulation, such as alternative splicng, miRNA regulation etc. which may lead to reduced or induced protein expression or the generation of other protein products, as well as degradation of mRNA without expression of a protein.

However, expression means generation of mRNA after transcription or proteins post translation!

Andreas Eisenreich , not if you mean ripe mRNA. There can be a lot of processes after transcription and before translation (capping, polyadenylation, editing, splicing, degradation, nucear export) that can unlink the rate at which a DNA sequence is transcribed into RNA molecules and the rate at which ripe mRNA (ready to be translated by ribosomes) is eventually produced.

Sure, in any case there is a difference between mRNA vs protein expression. Even capping etc. belongs to posttranscriptional processing.

There are 2 levels of gene expression.

Firstly, gene expression by transcription process which produce mRNA.

Secondly, gene expression by translation mRNA which produce protein.

There are more!

...

Thirdly, gene expression by physiological processes which produce a cell behaviour.

Fourthly, gene expression by organ-level processes which produce an organ function.

Fifthly, gene expression by organism-level processes which produce a organism phenotype.

...

population, species

...

ecosystem

...

society, economy, ...

...

gene ----(expression)---> phene

phene = any kind of observable characteristic that is genetically determined

Jochen Wilhelm

You have an interesting view over gene to phene. Can you suggest some literature where I can read more into the different levels of expressions you mentioned.

Best,

I would use "transcription" for mRNA and "translation" for protein, since in the latter case there is a radical change from a code to another.

Best regards

I kind of agree with many answers here, however I feel that sometimes these discussions get entangled in the natural ambiguities of the human languages. As in any form of communication, the context should be considered. For example, the majority of people would have no trouble understanding the sentence "artistic expression" within the context of a speech about the italian renaissance. But of course that "expression" can be fine-grained to the artistic expression of single individuals such as Botticelli or Gregorio Allegri, and moreover, they actually "expressed" their ideas, that collectivelly converged in space and time. Now consider that "ideas" are like "genes", the particular outputs (musical pieces or paintings) are like "proteins", and the whole italian renaissance is a "community". In all of those cases the term "expression" is all right, given then context.

Best regards.

Ankur Bothra

The link from gene to phene is classical textbook knowledge. I think ist also written clearly in Wikipedia. However, in https://en.wikipedia.org/wiki/Gene_expression, the definition given is "Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product." (bold by me) As such a "functional gene product", either proteins or functional RNAs (like tRNA, rRNA etc) are understood. For me, this is a very narrow view of molecular biologist. For the biology, function can be defined at many different levels, and all these levels can have profound impact on the biological system, which is a much richer context than just the cell-physiological function of a molecule with a sequence coded in the gene. That's rather obvious to me and I must admit that I don't have any papers to support this view. I would ask why the meaning of gene expression should be restricted to "molecules having a sequence coded in the gene" and not be continued to the further layers of biological effects (and beyond). The only literature I know that could be worth to read in this context is the book

The Concept of the Gene in Development and Evolution. Historical and Epistemological Perspectives. ISBN: 9780521771870.

I think the problem is that of understanding of terminologies and using them appropriately. To express a gene, we know that the processes of transcription and/or translation will have to occur and the phenotype which is the unit of expression in most cases is protein. It is the gene that is expressed as protein. The next thing that should follow is protein function. This is because a gene could be expressed in the form of a non-functional protein

Terms like gene expression, protein level or enzyme activity help to make a sentence easier to read. By specifying in another sentence (or another section of the document) what was measured and what technique was used to carry out the measurement, a reader will be able to infer exactly what the author is reporting.

I have been taught in class that a gene is expressed (or not), and that a protein is produced (or not). Therefore, the term "protein expression" is incorrect, no matter how frequently and widely it is used in the literature.

Olivera Francetic , agree. I think this is a good analogy:

a feeling (gene) is expressed by doing something, e.g. by producing a certain mimic or gesture (protein). One would not say that a smile is expressed; a smile is produced (by the coordinated action of many face mucles) as a happy feeling is expressed. I am also puzzled by the common misuse of the term "protein expression". As you said, I also think that "protein production" or "protein synthesis" would be the much better and more correct term. So the gene expression leads to RNA production (and if this is a coding mRNA) eventually to protein production.

What is also often confused is the production or synthesis itself and the concentration or amount present in the cell. Often, only the concentration is measured but it is claimed or deduced that the production/synthesis is measured. But the measured concentration is the result of a dynamic state where production and destruction play a role (e.g. blocking destuction can so be misinterpreted as increased production). It can be very misleasing to assume that changes in concentrations are changes in production rates.

This reminds me on Douglas Adams, who said: "The most misleading assumptions are the ones you don't even know you are making" :)

Technically a gene is expressed and protein translated, so it is produced. Although both terms can be used, it is better discriminate terms to avoid missunderstanding, for instance a gene can be highly expressed but not neccesarily results in more protein. The same analogy for proteins, a highly produced protein not neccesarily have a high gene expression.

I do not necessarily agree with some of the earlier negative remarks. I think the use of the term "protein expression" is OK and probably derives from the fact that there is no good term to describe the overall protein amount in a cell resulting from (gene)expression+translation+PT modification+degradation etc...

In this sense, "protein expression" is not used as a misnomer for translation, but is a catch-all term that refers to the final readout of all processes (which individually all can be regulated) that influence protein level.

One might ask then, why not to use the term "protein level", instead, and I guess the answer is that the word "expression" feels a bit more formal then "level". I think the use of "protein expression" is fine as a cumulative term, and people often use it for a lack of a better expression (no pun intended).

If you wanted to say something like "activation of X pathway leads to higher Y protein expression", might not sound the most scientifically formulated, but in fact, it carries the meaning that a probable functional change happens whose exact origin (e.g. translation/transcription/inhibition of degradation etc) might not even be known.

yes for mRNA we say gene expression but for proteins we say protein synthesis

For me, "synthesis" is more the process of being made (as opposed to degradation), wheras "expression" is more the fact that the product is present.