The document examines the hypothesis that the high evolutionary rate of CENP-A is due to coevolution with CENP-N. It finds that CENP-A evolves at a higher rate than CENP-N based on nucleotide divergence comparisons across species. Branch-site tests also show CENP-A has a higher proportion of neutrally evolving sites compared to CENP-N. Overall, the results do not support coevolution between CENP-A and CENP-N as the driver of CENP-A's high evolutionary rate. The higher rate is likely due to a greater influence of neutral processes on CENP-A evolution rather than positive selection pressures from coe

1. Alix Sayuri Souza Katsuyama
Iderval da Silva Jr. Sobrinho
Unidade Acadêmica Especial de
Ciências Biológicas,
Universidade Federal de Jataí.
alixsayuri@outlook.com

2. Introduction
The CENP-A has important functions for
cell division because it provides stability
of centromeric chromatin and functions
as a tag to identify centromere. It
directly interacts with two proteins,
CENP-C and CENP-N to initiate the
formation of the kinetochore.
CENP-A substitutes a non-
centromeric paralogous histone H3 in
centromeres and shares some
nucleotide sequence with H3.
Considering that disruption in the
assemblage of kinetochore would
impair meiosis, we would expect
CENP-A to be a conserved protein due
to its central role in initiating
kinetochore assemblage.
However, comparisons of CENP-A sequences
from different lineages have revealed that this
protein had evolved at high evolutionary rate,
unlike histone H3, which is relatively conserved
along its evolutionary history.
The coevolution of CENP-A with the other two
proteins (CENP-C and CENP-N) could be an
explanation for its high evolutionary rate.
We aimed to test the hypothesis of coevolution between CENP-A and CENP-N as the driven force
that had speed up their evolution.
We expect that both proteins would have similar evolutionary rates if a process of coevolution had
occurred between them.
Considering that changes in one protein would favor changes in another protein in a coevolutionary
context, we expect to find signals of positive selection in both.

3. Materials & Methods
Nucleotide sequences
search
Alignment Evolutinary model and
Phylogeny reconstruction
Substitution
saturation test
Branch-site
test of natural
selection
Nucleotide divergence
DAMBEPAML

4. Results
Species B. taurus R. novergivus M. musculus G. gallus
B. taurus 0.000 0.264 0.392 0.378
R. novergivus - 0.000 0.248 0.378
M. musculus - - 0.000 0.692
G. gallus - - - 0.000
Species B. taurus R. novergivus M. musculus G. gallus
B. taurus 0.000 0.198 0,200 0.332
R. novergivus - 0.000 0.097 0.374
M. musculus - - 0.000 0.391
G. gallus - - - 0.000
Table 1. CENP-A nucleotide divergence among different
vertebrate lineages. Nubers highlighted in orange indicate
greater differences in nucleotide divergence between CENP-A
and CENP-N in same lineage comparisons.
0%
20%
40%
60%
80%
100%
1
5
9
13
17
21
25
29
33
37
41
45
49
53
57
61
65
69
73
77
81
85
89
93
97
Purifying selection Neutrality
0%
20%
40%
60%
80%
100%
1
13
25
37
49
61
73
85
97
109
121
133
145
157
169
181
193
205
217
229
241
253
265
277
289
301
313
325
Purifying selection Neutrality
Figure 1. Relative probability of a site (codon) to be under
purifying selection or neutrality as estimated by Branch-site test.
A) Probabilities in CENP-A; B) Probabilities in CENP-N. No sites
under positive selection were detected in both proteins.
A)
B)
Table 2. CENP-N nucleotide divergence among different
vertebrate lineages. Nubers highlighted in orange indicate
greater differences in nucleotide divergence between CENP-A
and CENP-N in same lineage comparisons.
Codon
RelativeProbabilityRelativeProbability
Codon

5. Discussion & conclusions
A C K N O W L E D G M E N T S
Similarity in evolutionary rates between CENP-
A and CENP-N and positive selection signals in
both proteins could be the two major expected
evidences whether a coevolution had occurred
between both proteins. However, ours results
do not support both expectations, indicating
that a coevolutionary process could not explain
the high evolutionary rates found in CENP-A
Our results from Branch-site test (Figure 1 A
and B) and from comparison of nucleotide
divergence (Table 1 and 2) confirmed that
CENP-A is less conserved than CENP-N.
However, such higher evolutionary rate could
not be explained by positive selection, but by a
higher proportion of sites evolving under
neutrality if compared with CENP-N.