Scientific words - (Aug/04/2009 )

Would someone tell me which words are correct with hyphen, please?

overexpression or over-expression
upregulation or up-regulation
antitumor or anti-tumor
costimulatory or co-stimulatory
immunohistochemistry or immuno-histochemistry
downregulation or down-regulation
proapoptotic or pro-apoptotic
antiapoptotic or anti-apoptotic
prosurvival or pro-survival
chemoresistance or chemo-resistance
protooncogene or proto-oncogene


Thanks in advance.

There is no straight forward (or is it "straight-forward" or maybe "straightforward"?) rule; it usually depends on what part of speech the compound word functions as in the sentence. If it functions as an adjective, it's usually hyphenated (this is the same reason why one would write "a 25-kb segment of DNA..." but "the segment of DNA was 25 kb"). Another frequently followed rule is to hyphenate if the compound word will bring together two identical letters (thus anti-inflammatory rather than antiinflammatory).

See here, here, and here for further discussion. If in doubt, check a dictionary.