Germ-plasm specification and germline development in the parthenogenetic pea aphid Acyrthosiphon pisum: Vasa and Nanos as markers

Abstract

The germarium, oocytes and embryos of the parthenogenetic viviparous pea aphid Acyrthosiphon pisum are contained within a single ovariole. This species provides an excellent model for studying how maternally-inherited germ plasm is specified and how it is transferred to primordial germ cells. Previous studies have shown that germ cells are first segregated at the embryonic posterior after formation of the blastoderm. We used two cross-reacting antibodies against the conserved germline markers Vasa and Nanos, which specifically identified these presumptive germ cells, to investigate whether germ cells were determined during early development. We observed randomly-distributed weak expression of Vasa signals in the developing oocyte but no localization in the oocyte segregated from the germarium. Localized Vasa was not apparent until it was detected at the posterior in the embryo undergoing the second nuclear division. Nanos, on the other hand, was localized to a nuage-like structure surrounding the nucleus in the developing and segregated oocytes. At the beginning of the oocyte maturation division, Nanos localization shifted to the posterior and could be identified in successive stages until it was incorporated into the germ cells. Taken together, our results suggest that germ plasm is specified in the developing oocyte and that Nanos is an earlier germline marker than Vasa. Presumptive germ cells stained for Vasa remained at a dorsal location in the egg during middevelopment and then were guided into abdominal segments A1 to A6 during germ-band retraction. We infer that germ cells coalesce with segmented gonadal mesoderm during this period.

Hexapoda: Comparative Aspects of Later Embryogenesis and Metamorphosis

“…In parthenogenetic aphids ( Acyrthosiphon pisum ; Hemiptera), which have a germ plasm, Nanos protein is more strongly expressed posteriorly in the oocyte, and this asymmetric expression is maintained through germ cell formation (Chang et al 2006 ). Posterior localization of Vasa also occurs shortly after fertilization (Lin et al 2014a ), whereas vasa and nanos mRNA are ubiquitously distributed in mature oocytes and only become localized posteriorly when germ cells form at the blastoderm stage (Chang et al 2007(Chang et al , 2009.…”

Novel modes of localization and function of nanos in the wasp Nasonia

“…Within the insects, some degree of maternal localization of nos has been observed in all species so far examined (Curtis et al, 1995;Lall et al, 2003;Goltsev et al, 2004;Chang et al, 2006;Dearden, 2006), indicating that the posterior patterning function of nos may be conserved.…”

Apvasa marks germ-cell migration in the parthenogenetic pea aphid Acyrthosiphon pisum (Hemiptera: Aphidoidea)

“…As a consequence, oogenesis and embryogenesis occur within the ovariole. This morphological characteristic allows us to continuously observe how germ plasm is assembled during oogenesis, how it is incorporated into primordial germ cells, and how those cells migrate toward the somatic gonads (Brisson and Stern 2006;Chang et al 2006). Previous studies with cross-reacting antibodies have shown that the Nanos and Vasa proteins occur in the germarium, which lies at the anteriormost part of the telotrophic ovariole, and that they are localized to the posterior region of the egg chamber undergoing nuclear division.…”