E M B R Y O N I C H E M O G L O B I N S Y N T H E S I S
119
thesis. O'Brien (1961) employed chloramphenicol in his initial studies,
and it did not effect hemoglobin formation; but it is generally known
that this is an ineffective inhibitor of protein synthesis in higher organisms. The amino acid analog p-fluorophenylalanine, causes a profound
and definite inhibition of hemoglobin formation in late stage-8 and
stage-9 blastoderms. Hell (1964b) made a quantitative study of the effect
of this same analog; she found it did not affect nucleic acid synthesis,
but moderately inhibited both total protein synthesis and accumulation
of hemoglobin when it was applied to 1- and 4-somite embryos. Wilt
(1965a) showed that puromycin was an effective inhibitor of hemoglobin
synthesis. When it was employed at levels sufficient to cause inhibition
of hemoglobin accumulation, puromycin had no stage specific action. It
is probably justified to conclude protein synthesis is prerequisite for the
initiation of hemoglobin accumulation; preformed heme and globin
apparently do not spontaneously associate to form detectable amounts
of hemoglobin. Recently, Deuchar and Dryland (1964) have examined
the effect of the leucine and valine analog, a-methylnorvaline. They
found that it inhibited protein synthesis in explanted blastoderms, and
considerably reduced the amount of hemoglobin formed, in vitro. Examination of the residual hemoglobins formed in the presence of the analog
by electrophoresis did not reveal any unique new types of hemoglobins.
Lenicque (1959) reported that injection of extracts of adult blood
into the subgerminal cavity of head-fold blastoderms inhibited Hb produced in the ensuing 3 days of development by substantial amounts.
Although inhibition was also caused by blood extracts from which Hb
was removed by salting out, he concluded some "homologous inhibition"
was regulating Hb synthesis. The evidence presented does not seem
strong and further investigations are needed. Preliminary experiments
in our laboratory involving culture of blastoderms on media containing
purified Hb revealed no inhibition of embryonic Hb synthesis.
B. Stimulation of Hemoglobin Synthesis
Recently some studies employing specific agents to stimulate hemoglobin synthesis have opened another avenue of promise in the study of
the control of embryonic Hb synthesis. The kinds of effects which might
be anticipated are: (1) a general stimulation of the rate of hemoglobin
synthesis after it normally begins; (2) an acceleration of the time when
hemoglobin synthesis becomes detectable; (3) the appearance of hemoglobin in tissues or sites other than the blood islands. Malpoix (1964)
has recently studied the effects of RNA on the formation of hemoglobin
in explanted chick blastoderms. This was prompted by the transient
effects of RNA on enzyme formation, which have been reported over
the years, and the possible role of RNA in epigenetic transformation
119
thesis. O'Brien (1961) employed chloramphenicol in his initial studies,
and it did not effect hemoglobin formation; but it is generally known
that this is an ineffective inhibitor of protein synthesis in higher organisms. The amino acid analog p-fluorophenylalanine, causes a profound
and definite inhibition of hemoglobin formation in late stage-8 and
stage-9 blastoderms. Hell (1964b) made a quantitative study of the effect
of this same analog; she found it did not affect nucleic acid synthesis,
but moderately inhibited both total protein synthesis and accumulation
of hemoglobin when it was applied to 1- and 4-somite embryos. Wilt
(1965a) showed that puromycin was an effective inhibitor of hemoglobin
synthesis. When it was employed at levels sufficient to cause inhibition
of hemoglobin accumulation, puromycin had no stage specific action. It
is probably justified to conclude protein synthesis is prerequisite for the
initiation of hemoglobin accumulation; preformed heme and globin
apparently do not spontaneously associate to form detectable amounts
of hemoglobin. Recently, Deuchar and Dryland (1964) have examined
the effect of the leucine and valine analog, a-methylnorvaline. They
found that it inhibited protein synthesis in explanted blastoderms, and
considerably reduced the amount of hemoglobin formed, in vitro. Examination of the residual hemoglobins formed in the presence of the analog
by electrophoresis did not reveal any unique new types of hemoglobins.
Lenicque (1959) reported that injection of extracts of adult blood
into the subgerminal cavity of head-fold blastoderms inhibited Hb produced in the ensuing 3 days of development by substantial amounts.
Although inhibition was also caused by blood extracts from which Hb
was removed by salting out, he concluded some "homologous inhibition"
was regulating Hb synthesis. The evidence presented does not seem
strong and further investigations are needed. Preliminary experiments
in our laboratory involving culture of blastoderms on media containing
purified Hb revealed no inhibition of embryonic Hb synthesis.
B. Stimulation of Hemoglobin Synthesis
Recently some studies employing specific agents to stimulate hemoglobin synthesis have opened another avenue of promise in the study of
the control of embryonic Hb synthesis. The kinds of effects which might
be anticipated are: (1) a general stimulation of the rate of hemoglobin
synthesis after it normally begins; (2) an acceleration of the time when
hemoglobin synthesis becomes detectable; (3) the appearance of hemoglobin in tissues or sites other than the blood islands. Malpoix (1964)
has recently studied the effects of RNA on the formation of hemoglobin
in explanted chick blastoderms. This was prompted by the transient
effects of RNA on enzyme formation, which have been reported over
the years, and the possible role of RNA in epigenetic transformation