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)
Note that uchicago.edu newsfeed is terribly slow these days
More information about the Dros
mailing list