TABLE 1.

Survey of Piwi Proteins Across Animal Phylogeny: Somatic Expression Versus Germline Expression and Nuclear Expression Versus Cytoplasmic Expression

Organism	Homologues	Localization	Expression
			Germline*	Soma*
Fly	Piwi	Cytoplasm, Nucleus	PGCs (Megosh et al, 2006)	Embryonic somatic cells (Megosh et al, 2006)
		Nucleus	Ovary-GSCs, 16 cell cysts. Oocyte, Nurse cells (Cox et al, 1998)	Ovary - Terminal filament, Epithelial sheath cells, Follicle cells (Cox et al, 1998)
			Testis - GSCs, Gonialblasts (Cox et al, 2000)	Testis - Hub cells, Somatic stem cells, Cyst progenitor cells (Cox et al, 2000)
				Salivary Gland (Brower-Toland et al, 2007)
	Aub	Cytoplasm	PGCs (Harris and Macdonald, 2001)	Embryonic soma (Harris and Macdonald, 2001)
			Ovary - GSCs, all cyst cells, Oocyte, Nurse cells (Brennecke et al, 2007)
			Testis - GSCs, Gonialblasts, Spermatogonia, Spermatocytes (Nishida et al, 2007)
	Ago3	Cytoplasm	Ovary - Germline stem cells, All cyst cells, Oocyte, Nurse cells (Gunawardane et al, 2007)	Ovary- Faint in follicle cells (Gunawardane et al, 2007) Cap cells (Brennecke et al, 2007)
			Testis - GSCs, Gonialblasts, Spermatogoni a (Nagao et al, 2010)
Mouse	MIWI	Cytoplasm, Nucleus (Dense body) (Beyret and Lin, 2011)	Testis -Meiotic spermatocytes, Elongating spermatids (Deng and Lin, 2002)
		Unknown		Pancreas (Yan et al, 2011) Brain, Heart, Liver, Lung, Kidney (Lee et al, 2011)
	MILI	Cytoplasm, Nucleus (Dense body) (Beyret and Lin, 2011)	Testis - GSCs, Gonocytes, Spermatogonia, Meiotic spermatocytes, Spermatids (Kuramochi-Miyagawa et al. 2004, Unhavaithaya et al. 2009, Wang et al. 2009)
		Unknown		Mesenchymal stem cells (Wu et al, 2010)
	MIWI2	N ucleus, Cytoplasm	Testis - GSCs (Aravin et al, 2008)	Testis - Sertoli cells (Carmell et al, 2007)
Zebrafish	Ziwi	Cytoplasm	PGCs (Houwing et al, 2007)
			Ovary - Oogonia, Stage 1 oocytes (Houwing et al, 2007)
			Testis - Spermatogonia, Spermatocytes (Houwing et al, 2007)
	Zili	Nucleus	PGCs (Houwing et al, 2008)	Embryonic soma (Sun et al, 2010)
		Cytoplasm, Nucleus	Ovary - Oogonia, Stage l-IV Oocytes (Houwing et al, 2008)
		Cytoplasm	Testis - Spermatogonia, Spermatocytes, Spermatids (Houwing et al, 2008)
Frog	Xiwi	Cytoplasm, Nucleus(Mitotic/Meiotic Spindles)	Embryos Stage 1–20. Germline/Somatic separation unknown(Wilczynska et al, 2009)
			Ovary - Stage I - IV occytes, Mature oocytes (Lau et al, 2009)
		Unknown	Testis (Lau et al, 2009)
	Xili	Unknown	Embryos Stage 1–42. Germline/Somatic separation unknown (Wilczynska et al, 2009)
		Cytoplasm	Ovary - Stage I - IV occytes, Mature oocytes (Wilczynska et al, 2009)
		Unknown	Testis (Wilczynska et al, 2009)
Nematode	PRG1	Cytoplasm	Gonad- Germline stem cells, Mitotic/meiotic germ cells, Mature oocytes (Batista et al, 2008)
	PRG2	Unknown	Unknown	Unknown
Human	hiwi (piwil1)	Cytoplasm(Qiao et al, 2002) Nucleus, HEK 293T cells (Sugimoto et al, 2007)	mRNA Testis - Spermatocytes, Round spermatids (Qiao et al, 2002)
		Unknown		mRNA Hematopoietic stem cells (Sharma et al, 2001)
				mRNA Various tissues inc. Kidney, Heart, Brain, Liver, Muscle, Pancreas etc. (Sharma et al, 2001)
	hili (piwiL2)	Nucleus, HEK293T cells (Sugimoto et al, 2007)	cDNA Testis (Sasaki et al, 2003)
	piwiL3	Nucleus, HEK293T cells Sugimoto et al, 2007)	cDNA Testis (Sasaki et al, 2003)
	hiwi2 (piwiL4)	Nucleus, HEK293T cells (Sugimoto et al, 2007)	cDNA Testis (Sasaki et al, 2003)	cDNABone marrow, Leukocytes, Pancreas (Sasaki et al, 2003) mRNA Various tissues inc. Spleen, Lung, Liver, Brain, Heart, Kidney, Ovary etc. (Sugimoto et al, 2007)
Sea Slug(Aplysia)	Piwi	Unknown	Ovotestis (Rajasethupathy et al, 2012)
		Nucleus		Brain (Rajasethupathy et al, 2012)
Sea Urchin	Seawi	Cytoplasm, Nucleus(Mitotic Spindle)		Embryonic soma (Rodriguez et al, 2005)
			Ovary - Oocytes (Rodriguez et al, 2005)
Planarian	smedwi-1	Unknown	mRNA Neoblasts (Reddien et al, 2005)
	smedwi- 2	Unknown	mRNA Neoblasts (Reddien et al, 2005)
Polychaete Annelid (Capitella teleta)	ct-piwi1	Unknown	mRNA PGCs (Giani et al, 2011)	mRNA Somatic cells of embryo (Giani et al, 2011)
				mRNA Larvae - Brain, foregut, mesoderm (Giani et al, 2011)
			mRNA Immature oocytes (Giani et al, 2011)	mRNA Genital ducts (Giani et al, 2011)
				mRNA Posterior growth zone (Giani et al, 2011)
	ct-piwi2	Unknown	mRNA Primordial germ cells (Giani et al, 2011)	mRNA Embryonic soma (Giani et al, 2011)
				mRNA Larvae - Brain, foregut, mesoderm (Giani et al, 2011)
			mRNA Immature oocytes (Giani et al, 2011)	mRNA Genital ducts (Giani et al, 2011)
				mRNA Posterior growth zone (Giani et al, 2011)
Colonial Ascidian	Piwi	Nucleus, Cytoplasm	Gonadal primordia of ovaries and testes (Brown et al, 2009)
				Hemocytes (Brown et al, 2009)
				Endostyle-Epithelial cells, (Brown et al, 2009)
	EfPiwiA	Unknown	mRNA Pluripotent stem cells - Archaeocytes (Funayama et al, 2010)
				mRNA Choanocytes (Funayama et al, 2010)
	EfPiwiB	Unknown	mRNA Pluripotent stem cells - Archaeocytes (Funayama et al, 2010)
				mRNA Choanocytes (Funayama et al, 2010)
Ctenophore	PpiPiwi1	Unknown	mRNA Female gonad - Oocytes and nurse cells (Alie et al, 2011)
			mRNA Male gonad - Developing spermatocytes (Alie et al, 2011)
				mRNA Somatic stem cells of tentacle root, comb rows and aboral sensory complex (Alie et al, 2011)
	PpiPiwi2	Unknown	mRNA Female gonad - Oocytes and nurse cells (Alie et al, 2011)
			mRNA Male gonad - Developing spermatocytes (Alie et al, 2011)
				mRNA Unidentified cells of somatic origin (Alie et al, 2011)

^*Analogous expression in somatic, germline tissues are placed side by side. Blank boxes indicate no experimental evidence for PIWI expression.