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[Minnie Mouse]

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.

[HomeBrew]

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.