Cytogenetic characteristics of cell lines from Ixodes scapularis (Acari: Ixodidae)

Three new cell lines, IDE8 and IDE12 from embryos of northern specimens of Ixodes scapularis Say and ISE18 from southern specimens of I. scapularis, were compared cytogenetically via conventional karyotyping, C- and G-banding, and nucleolar organizing regions (NORs). The karyotypes were very similar. The standard karyotype in the three cell lines consisted of 28 chromosomes with 26 autosomes and XX (female) or XY (male) sex chromosomes. The X chromosome was the largest, and the Y chromosome the smallest chromosome of the karyotype. Constitutive heterochromatin (C-bands) was almost entirely restricted to the centromeric region. An additional interstitial C-band in chromosome 7 was an important notable characteristic of the three cell lines. In sets showing a similar degree of condensation, individual chromosomes of the three lines had identical G-banding patterns. In addition, there was no difference among the cells in number and position of NORs. There were approximately 100 G-bands per haploid set in chromosomes from cells in metaphase, with three to 18 G-bands in each chromosome arm. After staining with silver nitrate, interstitial NORs were identified in chromosomes 7, 10, and the X chromosome. Male cells had five and female cells had six NORs. These findings support the notion that I. scapularis and I. dammini Spielman et al. are conspecific.