Table 1.

RNA polymerase II, mRNA processing factors, and mRNA export factors revealed in early mammalian embryos.

Group of factors	Animal	Detected antigen	Method	Stage of embryogenesis	Reference
RNAP II	Mouse, rabbit	core of the RPB1 RNAPIIa, RNAPIIo	IF*, WB	1-cell–16–32 cell	[23]
	Mouse	RNAPIIa, RNAPIIo	IF, IEM	1-cell-2-cell	[24–27]
mRNA transcription factors	Mouse	TBP	IF	1-cell	[28]
		Sp1, TBP	IF Microinjection of Sp1-dependent luciferase reporter gene	1-cell-2-cell	[29]
		TBP, TAF1	IF	1-cell	[30]
		TBP, TBP2	IF, WB	1-cell-2-cell	[31]
		TFIID	IF	1-cell-2-cell	[24]
Splicing factors	Mouse	U1, U2, U4, U6 snRNAs snRNPs	ISH IF	1-cell-blastocyst	[32]
		U1 snRNA U1 snRNP	ISH IF	1-cell-blastocyst	[33]
		U1, U2 snRNAs snRNPs, SC35	ISH IF	1-cell–8-cell	[34]
		snRNPs, SC35	IF, IEM	1 cell-2-cell	[24, 35, 36]
		snRNPs	IF	1-cell-2-cell	[27]
		snRNPs	IEM	2-cell	[37]
		hnRNPs, snRNPs	IEM	1-cell–8-cell	[38]
	Bovine	U2 snRNA snRNPs	ISH, NB IF	1-cell-blastocyst	[39]
		snRNPs, SC35	IEM	1-cell–16-cell	[40, 41]
	Caprine	snRNPs, SC35	IEM	1-cell-2-cell	[41]
	Porcine	snRNPs	IF	1-cell-blastocyst	[42]
		snRNPs, SC35	IEM	1-cell–4-cell	[43]
	Hamster	U1, U2 snRNAs snRNPs SC35	ISH IF IF, IEM	1-cell–8-cell	[44]
mRNA export-related factors	Mouse	hnRNPs	IF, WB	1-cell–8-cell 1-cell	[34] [28]
		hnRNPs, Y14, Aly/REF, NXF1/TAP	IF, IEM	1-cell-2-cell	[45, 46]
	Hamster	hnRNPs	IF	1-cell–8-cell	[44]

 *Abbreviations: IF: immunofluorescence; IEM: immunoelectron microscopy; ISH: in situ hybridization; NB: northern blotting; RNAPIIa: hypophosphorylated form of RNA polymerase II; RNAPIIo: hyperphosphorylated form of RNA polymerase II; WB: western blotting.