TY - JOUR
T1 - Maternal and zygotic expression of a nanos-class gene in the leech Helobdella robusta
T2 - Primordial germ cells arise from segmental mesoderm
AU - Kang, Dongmin
AU - Pilon, Marc
AU - Weisblat, David A.
N1 - Funding Information:
We thank other members of our lab for many helpful discussions and assistance in preparing this manuscript. This work was supported by NSF grant IBN 9723114 to DAW and a fellowship from the Korean Research Foundation to DK.
PY - 2002/5/1
Y1 - 2002/5/1
N2 - The nanos-class gene of the leech Helobdella robusta (Hro-nos) is present as a maternal transcript whose levels decay during cleavage; HRO-NOS protein is more abundant in the D quadrant cells relative to the A, B, and C quadrants; and HRO-NOS is more abundant in the ectodermal precursor cell (DNOPQ) than in its sister mesodermal precursor (DM) (Pilon and Weisblat, 1997). Here, using in situ hybridization, we show that Hro-nos mRNA is broadly distributed throughout the zygote, is concentrated in both animal and vegetal teloplasm during stage 1 and is at higher levels in DNOPQ than in DM at stage 4b. Hro-nos expression increases after stage 7, as judged by in situ hybridization, developmental RT-PCR, and western blots; this increase must therefore represent later zygotic expression. Of particular interest, during stages 9 and 10, each of 11 mid-body segments (M8-M18) has a pair of Hro-nos positive "spots" comprising of one or two large cells each. These spots later disappear in an anteroposterior progression. We find that these Hro-nos-expressing cells are of mesodermal origin, arising in a segmentally iterated manner from the M lineage, and correspond to cells previously proposed as primordial germ cells (PGCs; Bürger, 1891; Weisblat and Shankland, 1985). These results support the proposal that nanos-class genes functioned in the specification of germline cells in the ancestral bilaterian and possibly in a separate process related to embryonic polarity in the ancestral protostome.
AB - The nanos-class gene of the leech Helobdella robusta (Hro-nos) is present as a maternal transcript whose levels decay during cleavage; HRO-NOS protein is more abundant in the D quadrant cells relative to the A, B, and C quadrants; and HRO-NOS is more abundant in the ectodermal precursor cell (DNOPQ) than in its sister mesodermal precursor (DM) (Pilon and Weisblat, 1997). Here, using in situ hybridization, we show that Hro-nos mRNA is broadly distributed throughout the zygote, is concentrated in both animal and vegetal teloplasm during stage 1 and is at higher levels in DNOPQ than in DM at stage 4b. Hro-nos expression increases after stage 7, as judged by in situ hybridization, developmental RT-PCR, and western blots; this increase must therefore represent later zygotic expression. Of particular interest, during stages 9 and 10, each of 11 mid-body segments (M8-M18) has a pair of Hro-nos positive "spots" comprising of one or two large cells each. These spots later disappear in an anteroposterior progression. We find that these Hro-nos-expressing cells are of mesodermal origin, arising in a segmentally iterated manner from the M lineage, and correspond to cells previously proposed as primordial germ cells (PGCs; Bürger, 1891; Weisblat and Shankland, 1985). These results support the proposal that nanos-class genes functioned in the specification of germline cells in the ancestral bilaterian and possibly in a separate process related to embryonic polarity in the ancestral protostome.
KW - Annelid
KW - Germline
KW - Helobdella
KW - Leech
KW - Nanos
UR - http://www.scopus.com/inward/record.url?scp=0036569705&partnerID=8YFLogxK
U2 - 10.1006/dbio.2002.0615
DO - 10.1006/dbio.2002.0615
M3 - Article
C2 - 11969253
AN - SCOPUS:0036569705
SN - 0012-1606
VL - 245
SP - 28
EP - 41
JO - Developmental Biology
JF - Developmental Biology
IS - 1
ER -