Natural Heteroplasmy and Mitochondrial Inheritance in Bivalve Molluscs.

Heteroplasmy is the presence of more than one type of mitochondrial genome within an individual, a condition commonly reported as unfavorable and affecting mitonuclear interactions. So far, no study has investigated heteroplasmy at protein level, and whether it occurs within tissues, cells, or even organelles. The only known evolutionarily stable and natural heteroplasmic system in Metazoa is the Doubly Uniparental Inheritance (DUI)-reported so far in ∼100 bivalve species-in which two mitochondrial lineages are present: one transmitted through eggs (F-type) and the other through sperm (M-type).

Germ cell line during the seasonal sexual rest of clams: finding niches of cells for gonad renewal.

Reconstitution and renewal of tissues are key topics in developmental biology. In this brief work, we analyzed the wintry spent phase of the reproductive cycle in the Manila clam Ruditapes philippinarum (Bivalvia, Veneridae) in order to study the gonad rebuilding that in this species occurs at the beginning of the warmer months. We labeled VASA homolog protein-a germ cell marker-and compared the histological observations of the spent phase with those of the previously analyzed gametogenic phase.

PL10 DEAD-Box Protein is Expressed during Germ Cell Differentiation in the Reptile Podarcis sicula (Family Lacertidae).

Among genes involved in the regulation of germ cell differentiation, those of DDX4/Vasa and the Ded1/DDX3 subfamilies encode for DEAD-box ATP-dependent RNA helicases, proteins involved in many mechanisms related to RNA processing. For the first time in reptiles, using specific antibodies at confocal microscopy, we analysed the localization pattern of a Ded1/DDX3 subfamily member in testis and ovary of Podarcis sicula (Ps-PL10) during the reproductive cycle. In testis, Ps-PL10 is expressed in the cytoplasm of spermatocytes and it is not detected in spermatogonia.

VASA expression suggests shared germ line dynamics in bivalve molluscs.

Germ line segregation can occur during embryogenesis or after embryogenesis completion, with multipotent cells able to give rise to both germ and somatic cells in the developing juvenile or even in adulthood. These undifferentiated cells, in some animals, are self-renewing stem cells. In all these cell lineages, the same set of genes, among which vasa, appears to be expressed.

The Expression of a Novel Mitochondrially-Encoded Gene in Gonadic Precursors May Drive Paternal Inheritance of Mitochondria.

Mitochondria have an active role in germ line development, and their inheritance dynamics are relevant to this process. Recently, a novel protein (RPHM21) was shown to be encoded in sperm by the male-transmitted mtDNA of Ruditapes philippinarum, a species with Doubly Uniparental Inheritance (DUI) of mitochondria. In silico analyses suggested a viral origin of RPHM21, and we hypothesized that the endogenization of a viral element provided sperm mitochondria of R.