Does "pro-" always precede "pre-" in a sequence? If so, why?

Question

In biological vocabulary, sometimes both pre- and pro- are used as prefixes to indicate something earlier in a sequence. For example, pro-B cells develop into pre-B cells, which eventually develop into mature B cells. And pro-microRNAs develop into pre-microRNAs, which develop into mature microRNAs.

When both pro- and pre- are used to mean "earlier to/prior to/before", does pro- always come first? Is this distinction used outside biological vocabulary? Does this come from some subtle difference in a classical language?

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_{* Of course, pro-B cells come after pre-pro-B cells. And pro-microRNAs come from pri-microRNAs, but "pri" is an abbrevation for "primary".}

Answer 1

This is a very interesting question. Unfortunately, I have not been able to find enough information to give more than a partial answer. But I hope it will be of some use.

According to the Oxford English Dictionary (OED), the prefix "pro-," meaning "before," comes mainly from the Greek prefix προ-. It is cognate with the Latin preposition pro meaning "for, before, in front of," and with the English word fore. More than 60 words with this prefix were adopted into Latin in antiquity, including prologus "prologue" and propheta "prophet," so Latin has been an important intermediate source of words with this prefix.

The OED indicates that the Latin prefix prae-, which corresponds to modern English pre-, was mainly used in Classical times with verbs and verbal derivatives, or to intensify the meaning of adjectives. There are also some cases where it modifies the meaning of nouns and adjectives, but the use before a noun to indicate an earlier version of that noun apparently only became common in post-Classical Latin and later languages.

The prepositional construction, in which pre- governs the second element, which was so rare in Latin, has in English received vast extension (as also in French), pre- being preferred to ante- as the opposite of post- in new formations, and often substituted for it, as in pre-Christian, prehistoric, pre-Darwinian, pre-reformation instead of ante-Christian, ante-historic, ante-Darwinian, ante-reformation. [...] It may also be combined with nouns in order to form compound nouns directly, as precancer n., preclimax n., [...] premyelocyte n., prepuberty n., etc. Compounds of this type are of relatively recent appearance.

So the distinction you mention does not seem to date back to Classical languages.

It does remind me of the use of hyper- in some contexts as a more extreme version of super- (discussed in the answers to this question: Which is higher — "hyper-", "ultra-" or "super-"?). In both cases, it seems like the more common term (super- or pre-) is used for the less extreme meaning. I have not found any cases where pre- and pro- are distinguished this way outside of biology.

I found one document about biology which seems to describe a slightly different naming scheme using "pre-pre-" instead of "pro-":

So-called B-ALL, for example, is based on progenitor cells of B-lymphocytes, while T-ALL forms from precursors of T-lymphocytes. A degeneracy in the early development stages is characterised by the prefix "pre". This results in the following ALL-subtypes:

• Pre-pre-B-ALL (now commonly referred to as pro-B-ALL)
• Common ALL
• Pre-B-ALL
• (mature) B-ALL
• Pro- and Pre-T-ALL
• Intermediate (cortical) T-ALL
• T-ALL

(Acute lymphoblastic leukaemia (ALL) - Brief Information)

Answer 2

As this question relates to biology, I will cite the classic example, but from molecular biology rather than cell biology, where history dictated a different nomenclature:

Pre-proinsulin

Proinsulin was the name given in 1967 to the single-chain (inactive) precursor of the two-chain mature biologically active insulin found in the blood. Later (in 1976) it was discovered that secreted proteins are made with an additional piece at one end (later removed) that directs them out of their originating cell, and that insulin (synthesized in the pancreas) fell into this category. The initial form of the protein was therefore termed pre-proinsulin.

Other pro-proteins

Nature’s strategy of producing proteins in an inactive form, to be later activated when needed by removing a portion (proteolytic cleavage) was subsequently found to extend to other protein hormones and a similar nomenclature adopted. Examples are:
proglucagon
prosomatostatin
pro-opiomelanocortin
In fact this is a variant of a similar mechanism to activate the digestive catalytic active proteins (enzymes) of the stomach, such as trypsin and chymotrypsin. The nomenclature adopted for these pro-proteins was quite different — the precursors had the suffix ‘ogen’ appended (e.g. trypsinogen). This was in the early years of the 20th century, long before anything was known about the structure of proteins. From a linguistic standpoint it is interesting that in the 1912 paper on trypsinogen the noun ‘enzyme’ is never used as such (there are three examples of ‘co-enzyme’), but that borrowed from the German — ‘ferment’ — appears 73 times.