Correction: Transformation Volume

Mark D. Garfinkel mg16 at kimbark.uchicago.edu
Sat Feb 18 10:21:03 EST 1995


In article <shall-1702951755040001 at macg203d.bio.purdue.edu>,
Stephen Hall <shall at bilbo.bio.purdue.edu> wrote:
>Earlier I posted a reply that 1% of egg volume or 100 nl was
>appropriate.  Actually, the egg volume is 10 x 10E-15 liters
>which makes the amount injected considerably less. My apologies.

	Gasp! This is like the Everett Dirksen line about "a billion
here, a billion there, and pretty soon you're talking about real money."

	Yes, Ashburner's Big Grey Book, page 216, says an embryo has a
volume of 10e-14 liter, but the same sentence says the *water* weight of
an embryo is 7.3 ug. Given that we're dealing with standard temperatures
& pressures, one can safely assume that the water content is at/near
unit-density, i.e., 1 gram per milliliter. Thus, the water content can
account for 7.3 nl all by itself. Add in ca. 2 ug of protein, at a typical
density of 1.4 g/ml, and that's another 1.4 nl. So, from chemical first
principles we arrive at a volume close to 10 nl, not 10 fl. Six orders of
magnitude is nothing to sneeze at. With all due respect to Michael, this
is commonly referred to as a "mistake."

	Given the roughly ellipsoidal dimensions of an egg/embryo, major
axis of 500 um and two minor axes of ca. 175 um -- one calculates an egg
volume of 16 nl [(4*pi/3)*abc, where a,b,c are the half-axis values].
Thus, Ashburner's Grey Book page 216 linear dimensions of an egg, plus a
bit of geometry, give a volume consistent with the above biochemical
calculation.

	As for injection volumes, see also Big Grey Book page 223, where
1-100 picoliters is given as the practical range. For an egg volume of
ca. 10 nl, the higher injection volume is 1% of total egg volume. This
rule of thumb dates back to the initial Spradling & Rubin (1982) P factor
transformation paper, and probably to the Van Deusen (1976) cell trans-
plantation paper upon which their injection methods were based.

	BTW, lest anyone forget: "nano" is the prefix for 10e-9, "pico"
for 10e-12, "femto" for 10e-15, "atto" for 10e-18, and "decca" for record
labels.

Mark
-- 
Mark D. Garfinkel (e-mail: garfinkl at iitmax.acc.iit.edu)
My views are my own, which is why they're copyright 1995 (c)
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