Behavior of sex chromosomes, autosomes, and the spindle during nonrandom segregation in a flea beetle

Microtubule distribution during meiosis I in flea-beetle[Alagoasa(Oedionychus)] spermatocytes: evidence for direct connections between unpaired sex chromosomes

“…We tested whether the sex-chromosome arms change during division from perpendicular to parallel to the spindle axis, as discussed by Kupfer and Wise (Kupfer and Wise, 2000a), by examining the relationship between the angle made between the chromosome arm and its associated spindle fibre at different stages of division. There is very little change in average angle, regardless of stage (Fig.…”

“…Virkki mentions the absence of a 'firm connection' between sex chromosomes, based primarily on observations using phasecontrast microscopy (Virkki, 1972). Three other publications claim to find no evidence for microtubule connections between sex chromosomes (Virkki, 1985;Kupfer and Wise, 2000a;Green-Marroquin et al, 2001). Unfortunately, these publications refer to unpublished work or do not present figures that clearly show the region between the sex chromosomes, and therefore there is little or no published evidence for or against a connection.…”

“…Although remaining at the cell periphery, the sex chromosomes do make connections to opposite poles and move towards opposite poles, but the details of this process are unknown. For example, it remains unclear how the unpaired sex chromosomes manage to orient to opposite poles; several studies reject the notion that there are connections or physical interactions between the sex chromosomes (Virkki, 1972;Virkki, 1985;Kupfer and Wise, 2000a;Green-Marroquin et al, 2001). With respect to sexchromosome spindle fibres, Virkki (Virkki, 1971;Virkki, 1972;Virkki, 1985) described them as syntelic (i.e.…”

“…However, Forer and Wilson presented data on kinetochore fibre lengths that seemed to argue against the interpretation that sex chromosomes move polewards with the autosomes (Forer and Wilson, 2000). Kupfer and Wise also dispute this claim, arguing that there is little or no polewards movement of sex chromosomes during anaphase (Kupfer and Wise, 2000a). To date, no one has addressed the mechanism for coordinating sex chromosome movements to opposite poles, nor have there been measurements of autosomal and sexchromosome movement during meiosis.…”

“…Virkki did not make sufficient measurements to address the relative contributions of movement to the pole ('anaphase A') and pole elongation ('anaphase B'), but Kupfer and Wise suggest from measurements on fixed cells that, whereas spindle length does increase between prometaphase and anaphase, spindle elongation in anaphase contributes little to autosome separation (Kupfer and Wise, 2000a).…”